Language Acquisition: Knowledge Representation and Processing
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Language Acquisition: knowledge Representation and
Processing
Antonella Sorace Caroline Hey cock Richard Shillcock Editors University of Edinburgh
1999 North-Holland Amsterdam - Lausanne - New York - Oxford - Shannon - Singapore - Tokyo
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First edition 1999 British Library Cataloguing in Publication Data A catalogue record from the British Library has been applied for. Library of Congress Catalog1ng-1n-Pub11cat1on Data
Language acquisition : knowledge representation and processing / edited by Antonella Sorace. Caroline Heycock, Richard Shlllcock. p. cm. Papers presented at a conference held Edinburgh, 1997. Includes b i b l i o g r a p h i c a l references. ISBN 0-08-043370-7 hc 1. Language acquisition—Congresses. I. Sorace, A n t o n e l l a . II. Heycock. Caroline B., 1960. III. S h l l l c o c k , Richard. P118.L2539 1999 40V.93--dc21 98-51947
CIP
ISBN: 0-08 043370-7 ©The paper used in this publication meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper). Printed in The Netherlands.
For
Teun Hoekstra (1953-1998)
in memory
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Contents A. Sorace, C. Heycock, R. Shillcock, Introduction: Trends and convergences in language acquisition research
1
K. Wexler, Very early parameter setting and the unique checking constraint: A new explanation of the optional infinitive stage
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T. Hoekstra, N. Hyams, Aspects of root infinitives
81
A. Radford, Genitive subjects in child English
113
B.D. Schwartz, The second language instinct
133
B.B. Tesar, P. Smolensky, Learning Optimality-Theoretic grammars
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P.W. Jusczyk, Constraining the search for structure in the input
197
S. Pinker, Words and rules
219
Author index
243
Subject index
253
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Lingua ELSEVIER
Lingua 106(1998) 1-21
Introduction: Trends and convergences in language acquisition research* Antonella Soracea'*, Caroline Heycockb, Richard Shillcockc " Department of Applied Linguistics, University of Edinburgh, 14 Buccleuch Place, Edinburgh EH8 9LN UK h Department of Linguistics, University of Edinburgh, Adam Ferguson Building, George Sqaure, Edinburgh EH8 9LL UK '' School of Cognitive Science, Division of Informatics, University of Edinburgh, 2 Buccleuch Place, Edinburgh EH8 9LW UK
Language acquisition has a special place in cognitive science, and has become a fertile ground for interdisciplinary research: this volume presents some current cutting-edge research which illustrates this fruitful convergence of endeavours. The contributions to the volume originated as invited talks presented at the Gala '97 Conference entitled 'Language Acquisition: Knowledge Representation and Processing', held in Edinburgh in April 1997.' The aim of the conference was to promote crossfertilisation across the different disciplines involved in research into language acquisition, and the collection presented here reflects this aim very directly.
1. Background The last decade has witnessed a significant shift in the cognitive paradigm applied to language acquisition. Until perhaps forty years ago, the study of language acquisition was largely restricted to the observation of individual case studies of child development (first language or LI acquisition), and to the improvement of teaching methods for foreign languages (second language or L2 acquisition). Theoretical ori* We would like to thank the authors contributing to this volume for the dedication and thoroughness that they demonstrated in the preparation, revision, and submission of their manuscripts. We are also grateful to the reviewers, whose insightful critiques and suggestions - often produced under severe time pressure - were invaluable. * Corresponding author. Phone: +44 131 650 3961; fax: +44 131 650 3962; e-mail:
[email protected] 1 The proceedings of the conference, containing all other talks and poster presentations, have been published as A. Sorace, C. Heycock and R. Shillcock (eds.), 1997. Proceedings of the Gala '97 Conference on Language Acquisition. Edinburgh: University of Edinburgh. 0024-3841/997$ - see front matter © 1999 Elsevier Science B.V. All rights reserved PII: S0024-3841(98)00028-X
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entations began to emerge largely as a result of the influence of generative linguistics, which firmly places language acquisition at the core of linguistic research. From this perspective, addressing the 'logical problem of language acquisition', that is, the ease and uniformity with which children acquire the ambient language in spite of the fact that they are exposed to qualitatively and quantitatively uneven input, motivated the research programme focused on the child's innate language-specific predispositions, or Universal Grammar (UG). However, from a different, more psychological perspective, tackling the problem of how language is acquired meant accounting for learning processes, that is, how the child's developing general cognitive abilities interact with the properties of the ambient input, and how both assist the child in the acquisition task. Similar orthogonal perspectives can still be found in the field of theoretical second language development, which is approached, on the one hand, by linguistically-oriented researchers with the intent of discovering whether and how Universal Grammar constrains second language grammars, and on the other hand by psychologically-oriented researchers with the aim of explaining second language learning as the result of general cognitive strategies and social interaction (see e.g. Bhatia and Ritchie, 1996). A different but related dichotomy that until recently characterised language acquisition research was the split between two different objects of inquiry: knowledge representation and processing mechanisms. Theoretical linguistic research into knowledge representation was addressed to the 'mental grammars' that learners construct on the basis of the universal notions and principles of Universal Grammar on the one hand, and the actual sentences they hear in their everyday experience on the other. Psycholinguists, in contrast, were primarily concerned with the processing mechanisms involved in actually using language, i.e. understanding and speaking, and how these mediate the acquisition process. This research ranges from speech perception (how listeners distinguish the sounds of their language) to parsing (how listeners group the words of a sentence into syntactic units) to constructing models of discourse (how listeners process the meaning of sentences in particular contexts). Language acquisition research on these topics focuses on the development of these abilities in the child, and how they interact with the developing knowledge of grammar. Developments over the last decade have changed the picture in profound ways, blurring the early dichotomies and bringing about an increasing diversification of perspectives and approaches. As Bloom (1994b: 1) puts it, '... there is no single process that one could call 'language acquisition'; instead, we are left with the task of explaining different acquisitions'. While this might look like fragmentation to the casual observer, we regard it as an unambiguously positive sign of vitality. Because of such diversification, current research exhibits a much higher degree of theoretical and methodological sophistication than was common even in the recent past. In so far as learnability constraints inform theories of grammar, developments in formal linguistics and language acquisition research go hand in hand; at the same time it has become clear that explanations of how the parser operates are central to the developmental problem: positive evidence can be informative only if the learner is able to assign it a structure (see Frazier and de Villiers, 1990). Moreover, experimental psychology and computer science have made available new techniques and concepts for
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the study of both young infants and children (see e.g. Jusczyk, 1997), and adult informants and learners (e.g. Bard et al., 1996). Powerful, fast computers are increasingly being used in concert with very large corpora of language - both text and transcribed speech - to derive generalisations about language that were not visible to smaller scale analyses. The establishment of the CHILDES database (McWhinney, 1995) has provided access to data from the acquisition of many languages, as well as procedures for analysis. A related development has been the growth of computational modelling as a field (e.g. Broeder and Murre, forthcoming), whose purpose is to implement theoretical constructs, thus forcing a very explicit formulation of assumptions. Connectionism, as one of the main computational paradigms of the last decade, has raised new questions concerning our understanding of learning and how it might occur in the brain. Because of their sensitivity to input, connectionist models are often seen in diametrical opposition to symbolic-deductive theories of language and language acquisition; however, this is not necessarily a valid opposition, since the initial definition of the architecture and learning algorithms of connectionist systems is important in understanding the emergence of linguistic structure in the model (see Plunkett, 1995). Connectionist models have become particularly well-known in the context of the acquisition of English verb morphology (Rumelhart and McClelland, 1986; Marcus, 1995; Hahn, Nakisa and Plunkett, 1997, among others), and have often been presented as alternatives to rule-based explanations of the process, giving rise to a debate which finds an echo in the paper by Pinker (this volume). The earlier polarisation between a focus on data and a focus on theory (e.g. 'Child Language' vs. 'Language Acquisition' in Ingram, 1987) also seems to have been largely abandoned, as shown by the recent publication of books on experimental methods for eliciting syntactic data from children (e.g. McDaniel et al., 1996; Grain and Thornton, 1998) - a visible sign of the much enhanced methodological standards that now characterise 'developmental linguistics'. The cross-disciplinary fertilisation of ideas is due to the fact that researchers of different orientations are now, to a much greater extent than before, actively acquainted with each other's work. The contributions to the present volume illustrate the convergence of distinct kinds of theories, tested against distinct kinds of data. Indeed, they reveal at least the basis of a common agenda in current language acquisition research. The papers on LI acquisition (Hoekstra and Hyams, Jusczyk, Pinker, Radford, Tesar and Smolensky, and Wexler), exhibit a consensus on the following issues: • Language acquisition is a tightly constrained process that is biologically predisposed to follow certain paths; it is, in fact, even more constrained than was previously thought. • Basic knowledge of language is acquired very early, in the first two years of life, much of it probably before the emergence of production. • Much acquisition is perceptual, and not dependent on direct negative evidence. Schwartz's paper, the only one that deals with theoretical L2 acquisition, points to another generalisation on which there is much agreement in this field:
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• Non-native grammars may be non-convergent with respect to the target grammar, but are UG-constrained. Taken together, the papers in this volume offer an explanation of constraints on language development, for both LI and L2 acquisition, that crucially hinges on an analysis of early transitional grammars, and particularly on a precise definition of what constitutes the acquirer's 'initial state'. A theory of L2 acquisition, in addition, has the responsibility of accounting for final states, which are not deterministically and uniformly attained, as in LI acquisition, but often differ from the target and from each other. Before introducing the content of the individual papers, we will provide some background to the discussion, focused around these points of convergence. Our review of the main issues will necessarily be brief and restricted to questions of relevance to the papers included in this volume (for more details, and different points of view, see Bloom, 1994a; Fletcher and McWhinney, 1995), but will touch on some of the central concerns in the debate, including controversial questions that have not yet received an answer. 2. Language acquisition is a tightly constrained process The existence of constraints on acquisition makes life easier for the learner, facilitating fast convergence on the target. However, it raises the opposite question: why do children not converge on the target immediately? In other words, why is acquisition not instantaneous, or why is there a 'developmental problem' as well as a 'logical problem'? Consequently, even given a shared assumption of universal constraints on acquisition, it is still an open question as to how much of UG characterises the initial stage: are all the principles of UG there from the start, or are at least some of them genetically scheduled to mature at a later stage? There is a lively debate in the literature between proponents of the Continuity Hypothesis (e.g. Hyams, 1986, 1996; Clahsen, 1992; Penner and Weissenborn, 1996, among others) and supporters of the Maturationist Hypothesis (e.g. Borer and Wexler, 1987; Radford, 1990; Felix, 1992): this debate is also reflected in the present volume. Simplifying somewhat (see Meisel, 1995 for fuller details), the Continuity Hypothesis holds that UG in its entirety constrains child grammars at all stages of development: delays and child-adult differences at any stage are due not to divergences in syntactic representation, but rather to lack of knowledge in domains other than UG. This position is the most parsimonious in that it requires the fewest developmental changes (Pinker, 1984; Grain, 1991, among others); it is illustrated in this volume by Hoekstra and Hyams' contribution. By contrast, the Maturationist Hypothesis maintains that not all of UG is present in early child grammars. There are two kinds of maturationist position. In one, often called the 'Structure-building' account, it is argued that functional categories (e.g. INFL and CP) are absent in children's earliest production because they mature in the third year of life (e.g. Radford, 1990, 1996; Vainikka, 1993/94; Lebeaux, 1988;
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Powers and Lebeaux, 1998). The other position - often labelled 'UG-constrained maturation' - holds that principles of UG are present from the start, but specific elements of linguistic knowledge are genetically scheduled to become operative at a later stage. For example, Borer and Wexler (1987, 1992) propose that A-chains, which are involved in the derivation of passive verbal constructions and other instances of NP-movement, are initially unavailable to children. Early child syntax is more restrictive than adult syntax because it is affected by developmental learning constraints ('proto-principles', in Borer and Wexler's (1992) definition) that uniquely characterise child grammars and generate a subset of the representations that are possible in adult grammars. This position is argued for in Wexler's paper (this volume), which proposes that one of these early constraints is responsible for a variety of features of early child grammars, such as non-finite forms in matrix clauses, oblique case assignment, and null subjects. Thus, both maturationist positions regard change as a series of grammar-internal restructurings, due either to the maturation of late-appearing UG principles or to the withering of developmental constraints, leading to the consequent reinterpretation of the input data. A different explanation of what constrains child grammars, which is however consistent with many of the assumptions of the Continuity position, is offered by Optimality Theory (OT) (Prince and Smolensky, 1993). OT is a formal theory of UG that assumes that (a) universal constraints are ranked in language-specific ways, and (b) constraints can be violated: more specifically, lower-ranked constraints may be violated in order to satisfy higher-ranked constraints. Within this approach, the child is assumed to be equipped with knowledge of the abstract form of an OT grammar, as well as with an interpretive parser, which is essentially the same mechanism used by the competent adult speaker in assigning a structural description to an overt form in the input (see Smolensky, 1996; Tesar and Smolensky, 1998), and a constraint demotion mechanism, which is a procedure for learning constraint rankings. Learners use this knowledge of the abstract form of an OT grammar from the start to refine their ranking hypotheses and converge on the ranking required by the target language. In so doing, they rely on an iterative algorithm, which involves repeated alternations between structure-assignment (by means of interpretive parsing) and grammar learning (by means of constraint demotion). Tesar and Smolensky (this volume) show that the iterative algorithm can be proved to converge very fast on the basis of limited evidence, hence confirming the effectiveness of the constraints imposed by OT on the acquisition space. Whereas speech perception researchers have traditionally been less uniformly committed to the idea of domain-specific constraints, they are in agreement that children's sensitivity to certain properties of the input develops at a very early stage in infancy. Research on language perception has increasingly revealed its scope for illuminating language acquisition. As in the rest of language acquisition research, a dominant question has been the issue of what representations or processes are innate and specific to language, as opposed to being learned and grounded in general, even non-species-specific, perceptual and cognitive constraints. The field has relied on the development of methods to study infant speech perception; techniques involving non-nutritive sucking (in the youngest infants) and head-turning behaviour (in older
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infants) have led to a clearer understanding of the discriminations that infants can make between different speech stimuli, but the issue remains of whether the discriminations are being made at a linguistic or non-linguistic level. Nonetheless, researchers agree on the fact that children's sensitivity to potentially linguistic properties of the input develops very early in the first year, in response to the speech input, and is shadowed by a decline in sensitivity to distinctions not frequently found in the input (see Werker, 1993, for a review.) Although there have been demonstrations that other species are capable of making some of the same distinctions (see, e.g., Kuhl and Miller, 1975), it is still possible that the speed of learning the discrimination, or the initial tuning to it, reflects some distinctly human capability. Although research has strengthened the claim that at least some parts of language acquisition, such as the role of perceptual constancy for instance, reflect general cognitive and perceptual abilities, such research cannot rule out the possibility that differences between human and nonhuman performance reflect the use of innate, language-specific components to acquisition, or at least the very early recruitment of general cognitive and perceptual processes to an emerging language module. Computational perspectives have become increasingly influential, allowing the implementation and testing of particular theories (see, in particular, the debate concerning learning of the past tense, below) and the statistical analysis of large corpora of speech to children (see, e.g., Cartwright and Brent, 1994; Cairns et al., 1997). Such studies may reveal a more sophisticated picture of the information that is in the speech stream, offsetting somewhat the traditional notion that the speech input is irredeemably noisy and impoverished. In general, though, such studies can only show that the information is potentially available, and they are not able to say that a particular generalisation is actually used, or that a particular source of information is more salient than another for the infant. Also from this computational perspective (Elman, 1993; but see also Newport, 1990), it has been proposed that an important general constraint that mediates language acquisition is the size of the processing window onto the speech input granted by the infant's developing memory and attention: a very small window may be advantageous in allowing the infant initially to notice and encode only very local relationships within the speech, and thereby prioritising local over long-distance dependencies - 'less is more'. Indeed, Jusczyk (this volume) reports experiments on the effect of larger or smaller amounts of intervening material in processing syntactic discrepancies in speech heard by infants, demonstrating the potential relevance of this perspective. In general, the increase in knowledge about the infant's sensitivities to the information in the speech input has lent credence to the tradition of 'bootstrapping' theories, in which one type of information - syntactic, semantic or prosodic, in various approaches - provides evidence for the establishment of structured relationships at another level. Thus, for instance, in prosodic bootstrapping, prosodic (and other) information in the speech signal is taken to provide evidence for syntactic structure (Gleitman and Wanner, 1982; Morgan and Demuth, 1996). Overall, then, research on the infant's developing sensitivities to different aspects of the speech signal has provoked models of how the infant develops competence at the
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lexical and the syntactic levels, and has provided a richer context for the ongoing debate about the potential role of innate, specifically linguistic capacities in language acquisition.
3. Basic knowledge of language is acquired very early The early appearance of linguistic knowledge has long been regarded as among the best evidence for UG constraints. There is now a substantial body of evidence that suggests that much knowledge of complex syntactic properties is acquired fast and is in place shortly after the child's second birthday (see Hoekstra and Schwartz, 1994; Clahsen, 1996; and references herein; for a note of caution, see Atkinson, 1996): this knowledge includes basic word-order parameters and the properties of inflection. It is still controversial, however, whether such evidence can be said to characterise the initial stage of syntactic development, or whether it belongs to a stage subsequent to 'First Syntax' (see Paradis and Genesee, 1997, for comments). Whereas it is possible to argue in favour of one or the other possibility on theoretical grounds, only extensive research on pre-linguistic and one-word stages can provide empirical evidence relevant to this question. This is an area where speech perception and linguistic research have a lot to offer each other; as Jusczyk's paper (this volume) suggests, there is a promising line of investigation that explores the existence of universal linguistic constraints in very young infants, using experimental techniques, such as the Headturn Preference Procedure, suited to the pre-linguistic stage. What about the other side of the conundrum, that is, the obvious and protracted divergences between child and adult grammars? Many current accounts within the UG framework favour an explanation of nonadult forms produced by children in terms of underspecification of functional categories, which is held to be responsible for a range of morphosyntactic reflexes. However, the term 'underspecification' has not received a uniform interpretation in the literature. For Wexler (1994; this volume), it means the absence of a particular functional head (Tense or Agr), which may itself be caused by the presence of a developmental constraint in child grammars (in a similar vein, Rizzi's (1994) 'Truncation Hypothesis' assumes that child grammars may lack the principle 'CP = root'. Hyams (1996), on the other hand, argues that functional nodes, both in the clausal and nominal domains, may be underspecified in the sense of 'unindexed' - not part of syntactic chains that anchor the event or the referent. Hoekstra and Hyams (this volume) develop this analysis further, arguing that this lack of anchoring can be traced back specifically to the underspecification of the Number feature. Yet another definition of underspecification is provided by Clahsen, 1996; see also Clahsen et al., 1994) within the Lexical Learning Hypothesis. The assumption of this theory is that UG principles are available in early child grammars, but language-specific functional heads and their feature specification are learned gradually on the basis of exposure to lexical and morphological items in the ambient input. Early child grammars are characterised by underspecified functional projections that have fewer features than
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the corresponding positions in adult grammars; other functional projections, as well as the syntactic features required by the target language, are gradually added as a result of lexical learning. All these theories adopt underspecification as an explanatory mechanism that is meant to account for non-adult forms and developmental delays in child grammars under a UG-constrained scenario. The introduction of underspecification into child grammar has the advantage of making the acquisition process more strongly deductive than it was before. Particular syntactic phenomena that were thought to be independent 'parameters' are now seen as derivative. The Agr/Tense underspecification account, for example, allows us to see how phenomena such absence of finite morphology, null subjects, lack of determiners and oblique case-marking are related. However, an underspecified grammar may exhibit certain theoretically problematic features. The most obvious of these is optionality, which is limited in adult grammars but quite pervasive in child grammars. Optionality is difficult to account for in current formal theories of grammar: this is true of both Minimalism and Optimality Theory. What does it mean to say that the child can, for example, optionally project either Agr or Tense (Wexler, this volume), or optionally choose CP as the root node (Rizzi, 1994)? The favoured solution (and the only one permissible in current theoretical terms; see Fukui, 1993; Anttila, in press) assumes that both a derivation with e.g. Tense and one without are equal in terms of economy: this assumption is exemplified in Wexler's paper (this volume), and by the notion of a 'tie' between constraints in Tesar and Smolensky's paper (this volume). However, this type of solution leaves much to be explained: in particular, it provides no insight into the relative frequency of the variants, far less the observed systematic changes in this over the course of development. One possible way out of this problem would be to introduce probabilities into the grammar, which would obviously affect some of the current basic foundations of formal grammatical theories: recently, some modifications of Optimality Theory have been proposed which essentially adopt this solution (Hayes, in press; Boersma, 1997). Another solution to the optionality generated by underspecification, consistent with current Minimalist assumptions about the nature of grammar, is to exclude it from the domain of syntax proper and ascribe it not to deficits in syntactic representations, but rather to non-target knowledge in other domains, such as pragmatics or semantics. Hoekstra and Hyams (this volume) thus attribute children's freedom to leave Number underspecified to a lack of knowledge of interface conditions. Wexler (this volume) allows for derivations in child grammars which omit Tense and yet converge because Tense is not required by the computational system, but only by a principle of the interface with the conceptual system. Future research will be needed to explain how exactly underspecified grammars become specified, and how exactly knowledge of 'interface' conditions develops and interacts with the grammar, since there is every reason to believe that this development is as strictly constrained as that of syntactic knowledge. The more child grammars are constrained (particularly under the maturationist scenario) the more the acquisition paths for different languages should resemble each other. Wexler (this volume), for example, argues that what look like language-
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specific differences in the distribution of optional infinitives reduce to the application of a single developmental constraint plus knowledge of the default Case and knowledge of a specific value for the Null Subject parameter. An obvious testing ground for these theories is bilingual (LI) acquisition, in which two languages develop in the same brain, and thus the effect of individual variation is eliminated. Whereas the evidence from studies of bilinguals is still limited, it suggests that functional categories may develop at different times in different languages acquired simultaneously (see Paradis and Genesee, 1996, 1997), thus providing an interesting challenge to the maturationist account.
4. Much acquisition is perceptual Early models of language acquisition within the Principles and Parameters framework emphasised the distinction between UG principles, assumed to be known innately, and language-specific parameters, which had to be learned on the basis of exposure to a particular language. These models therefore allowed for the possibility that children could explore the range of parameterised options permitted by UG, and sometimes mis-set parameters (e.g. Hyams, 1986; Jaeggli and Safir, 1989; Roeper and Williams, 1987); they proposed solutions to the problem of how children retreat from such errors (cf. Berwick, 1985; Matthews and Demopoulos, 1989) in the absence of negative evidence. Recent research, by contrast, suggests that many syntactic and perceptual parameters are set at a very early stage. Indeed, parameters may be set before production abilities emerge (thus showing the implausibility of theories that assume that the child learns from his or her own production (e.g. Elbers, 1995, forthcoming)); this is definitely the case for perceptual parameters, but has not been conclusively demonstrated for syntactic parameters. One of the consequences of early parameter setting is that learning from negative evidence is an impossibility, since negative evidence - at least in the narrow sense of explicit correction - presupposes the presence of incorrect forms in children's production. Considerably less clear is the role of indirect negative evidence: if learners expect to find a form in the input which does not occur, it is not obvious how long they have to wait before concluding that it will never occur (see Valian, 1990). The role of indirect negative evidence within Optimality Theory is much more defined, as discussed by Tesar and Smolensky (this volume). Since learners are assumed to have access to the universal Gen function, they know what the competitors are for each piece of positive evidence to which they assign a structure; given the theoretical requirement that there be only one optimal candidate within each set, learners will indirectly know that the competitors are sub-optimal. The other important consequence of the extent to which children learn without any access to direct negative evidence is that a new burden is put on 'triggering' as an explanation of what causes developmental changes. Even a short review of the conceptual and empirical problems raised by the notion of triggering is a task that cannot be accomplished here (see Atkinson, 1992 for a discussion). Suffice it to say that triggering, as opposed to learning, involves less exposure to the input and a
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much narrower margin for retreating from errors: external triggers must therefore have precise structural properties that allow the child to converge fast on the target. Formal approaches to learnability have addressed these questions (Gibson and Wexler, 1994; Clark, 1992; Clark and Roberts, 1993). Triggers, as already mentioned, may also be grammar-internal: under the maturationist scenario, what causes a shift from one stage to the next are changes internal to the acquirer due to her reaching particular developmental stages. The attainment of these developmental milestones confers on the child the ability to access properties of the input that have hitherto been filtered out.
5. Non-native grammars may be non-convergent but are UG-constrained The acquisition of a second language in adulthood is evidently different from the acquisition of a native language because the adult learner already knows (at least) one other language: the initial state of the child and of the adult are not the same. It is also clear that the attainment of native-like competence in a second language is the exception rather than the rule. Unlike children, who reach perfect mastery of whatever language they are exposed to, many adults display varying degrees of 'imperfection' in second languages, even after long periods of exposure, and even those who are capable of native-like performance often have knowledge representations that differ considerably from those of native speakers (Sorace, 1993). So not only the initial state, also the final state of the child and of the adult learner are different. Yet there are important, albeit less obvious, similarities between the two processes, as much recent theoretical research on second language development has demonstrated. The central concern for a theory of L2 acquisition is to determine whether, and to what extent, UG still constrains the process: given that adults can rely on general cognitive abilities, it is at least conceivable that they may use them, instead of UG, in the task of learning a second language, particularly if UG, for neurological reasons, ceases to operate after a certain age. What emerges from recent research, however, is a picture in which UG plays a fundamental role in shaping non-native grammars at all stages of development. Whereas theories that posit an essential identity between the processes of LI and L2 acquisition seem both intuitively and empirically implausible (see the discussion in Epstein et al., 1996), there is now a consensus on the fact that UG and the learner's LI are the two forces that interact to shape L2 development (see White, 1989, 1996; Schwartz and Sprouse, 1994). Precisely how much of the LI characterises the initial state, however, is an open question, as Schwartz's paper (this volume) illustrates very well. The position Schwartz holds is that the LI grammar in its totality represents the L2 initial stage; the learner then progressively restructures this system, on the basis of exposure to the input and a failure-driven mechanism which causes the reanalysis of input that cannot be accommodated by the current grammar. This line of research requires going beyond the 'identity assumption' (Sorace, 1996), namely the belief that the only proof of the availability of UG is the correspondence/identity between the learner's grammar and the L2 grammar, in terms of either interim stages
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or final states: non-native grammars may diverge from the L2, but they are still 'natural' grammars, instantiating options that are within the UG-constrained range (Finer and Broselow, 1986; Thomas, 1991; White, 1996). As Schwartz (this volume) suggests, such divergence is to be expected precisely because the adult learner's initial state is different from the child's: in progressively restructuring their grammars upon exposure the adult learner necessarily resorts to different analyses from those entertained in LI acquisition, and resorts to a multiplicity of UG mechanisms that are not necessarily needed by the LI acquirer at corresponding stages of development. Also to be expected is the fact that L2 grammars are generally characterised by protracted optionality, in contrast with child grammars for which optionality is a transient phenomenon. L2 learners may not receive sufficiently robust evidence to be able to expunge non-target optional variants, regardless of whether these are derived from the LI or not. Optionality, however, may not necessarily be the hallmark of a 'rogue' grammar (contrary to what is suggested in e.g. Towell and Hawkins, 1994): as discussed in Schwartz's paper (this volume), it may be a property of a natural language grammar (see also Robertson and Sorace, in press; Sorace, 1998).
6. Overview of papers The phenomenon on which Wexler's chapter is based is the Optional Infinitive (OI) stage also analysed (with a different focus and conclusions) in the chapter by Hoekstra and Hyams. Crucially, in some languages children go through a stage of alternating between finite and nonfinite verb forms in root clauses; that is, they (optionally) produce Root Infinitives (RIs). Other constraints on finite and nonfinite forms found in the adult language are, however, already mastered. Wexler offers a radically new analysis of the OI stage which is also presented as a demonstration of two larger claims, one about the course of language acquisition and one about the relation between developmental psycholinguistics and linguistic theory. With respect to the course of language acquisition, Wexler argues that, in contrast to what he takes to be generally accepted assumptions, 'basic parameters' are set correctly, and the properties of inflectional elements learned, very early - at the latest by the time there is any production evidence for them at the two-word stage - and that, by contrast, some aspects of UG have to mature over time. As for the relation between developmental psycholinguistics and linguistic theory, Wexler makes a case for results from the study of child language being crucial to linguistics, and in particular being in some cases more informative about the nature of UG than results from adult language. Wexler's starting point for his reanalysis of the OI stage is the consensus in the literature that the OI stage is principle-based and not construction-specific. Children who alternate between finite and nonfinite forms in various languages show knowledge of the basic parameters of verb movement at the earliest observed stage. This is one instance of Wexler's general hypothesis that parameters are set correctly at the latest by the earliest observable stage of production; a further instance is his differentiated analysis of missing subjects in the language of children exposed to pro-drop
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and non pro-drop languages. Wexler then considers the Agr/Tense omission model developed by Schiitze and Wexler (1996), which accounts for the Nom/Acc case alternation on the subjects of root infinitives. One aspect of this analysis is the availability of default case for the subject when Agr is absent. This availability raises the question of what forces leftward movement of the subject from its assumed base position in the Verb Phrase in these sentences, since the original proponents of the VP-internal subject hypothesis argued that this movement (in adult languages) was driven by the need for the subject to be assigned nominative Case. More recently, however, Chomsky (1995) has argued on the basis of quite different data that the necessity for a subject to appear in this external position is due to a feature of the functional heads requiring a DP, rather than to the assignment of Case. For adult grammars the argument is somewhat indirect and depends on assumptions about intermediate stages of a derivation; this is the immediate basis for Wexler's contention that child language can in some cases provide a clearer view of UG than adult grammars (see Deprez and Pierce, 1993 for similar arguments). In the second part of the chapter, Wexler addresses the question of why children acquiring null-subject languages do not go through an OI stage. He explains the existence of OIs in non-null subject languages in terms of a developmental constraint, the 'Unique Checking Constraint', which differentiates the child grammar from the target adult grammar. By assumption, this constraint is present in all children, but given additional assumptions about the nature of Infl in null-subject languages it operates vacuously in these languages; hence the children's output is identical in the relevant respects to the adults'. The presence of the UCC is an example of UG-constrained maturation, which makes child syntax more restrictive than adult syntax: derivations that are allowed in adult grammars are excluded by child grammars. However, in one sense it seems that the children's syntax is (optionally) less restrictive: after all, root infinitives are (generally) not grammatical in the relevant adult grammars. Wexler proposes that representations with OIs are convergent (a narrower notion than 'grammatical') because they only violate interface conditions which require the presence of Agr/Tense (i.e. this requirement is a interpretive/conceptual property, rather than a property of the computational syntax). One might then suppose that children are not initially aware of the relevant interface condition, or that there is a preference for a convergent derivation, even if an interface condition is violated. But in either case, children should never produce adult-like finite sentences that violate the UCC; but they do - some of the time. Thus at this point we face the problem of optionality. Wexler offers two potential solutions: one is to suppose that the UCC itself applies only optionally. The other is to adopt a position more familiar within Optimality Theory: the interface condition and the UCC are equally ranked constraints, and optionality is the result of a tie between two derivations, each of which violates one of these constraints. As Wexler himself notes, neither of these solutions seems wholly satisfactory; the question of optionality remains essentially open. Like Wexler's, Hoekstra and Hyams' paper focuses on the properties of RIs in early child grammars. In common with Wexler, Hoekstra and Hyams assume early convergence of morphosyntactic properties: delays and non-adult forms are due to
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lack of interpretive knowledge that does not belong to the core of the computational system. Also in common with Wexler, it is assumed that some functional head is lacking - or at least underspecified - in the child grammar. For Wexler, either Tense or Agr may be absent; for Hoekstra and Hyams, it is the functional head Number that may be underspecified. This is crucial to the phenomenon of RIs in their theory, since they propose that number morphology is one of the possible ways in which finiteness may be expressed. Thus if Number is underspecified in a language like Dutch, where finiteness is expressed through number morphology, the result will be a nonfinite clause. In a language like Japanese, on the other hand, where finiteness is expressed through tense morphology, the same underspecification will not result in an infinitive. Thus Hoekstra and Hyams, like Wexler, propose an explanation of the cross-linguistic distribution of RIs that relies on the interaction of a non-language specific developmental phenomenon with independently motivated cross-linguistic differences, although they differ in their proposals for both ingredients of the explanation (for Wexler the crucial cross-linguistic difference is whether or not Infl may itself be nominal, in some sense (the empirical evidence for which is the existence of Infl-licensed pro-drop in the language). It might be thought that these different ingredients would yield a very different division of languages, and hence an easy empirical metric for comparing the two analyses, but given the (still contentious) correlation between rich inflection (which presumably entails encoding more than just a number distinction) and subject pro-drop, the predictions actually converge to a very large extent. Whether or not they are empirically equivalent on this point may depend on whether a principled distinction can be made between the kind of prodrop found in the southern Romance languages ('Infl-licensed' pro-drop), and the kind of pro-drop found in Japanese and Korean. The work of Wexler on the one hand and Hoekstra and Hyams on the other does differ considerably in focus: Hoekstra and Hyams include as evidence for their analysis extensive discussion of the interpretive properties of RIs. Most centrally, they take up earlier observations that RIs in all languages where they have been noted, with the exception of English, only occur with eventive verbs; these observations are synthesised into their Eventivity Constraint. This difference in interpretation between English and other languages that allow RIs they argue to correlate with other differences, both interpretive and syntactic. RIs in English differ from those in other languages in not having exclusively modal interpretations; in addition, they occur with an overall higher frequency, and allow a full range of subject types (whereas in a language like Dutch RIs occur almost exclusively with null subjects or noun phrases with no overt marking for number). These differences Hoekstra and Hyams trace back to a peculiarity of the English infinitival form in adult grammar: unlike all the other languages that allow RIs, the English infinitive is morphologically unmarked. This variation in infinitival morphology is crucial to their analysis of the differences between RIs in English and the other languages in which they occur. On the one hand, they argue that the modal interpretation of RIs in children is a direct reflection of the [-realised] feature of infinitival morphology; following Giorgi and Pianesi, 1997, they claim that this interpretive difference can be detected in the dif-
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ferent interpretations of infinitive forms in the adult grammars also. On the other hand, they propose that the lack of overt morphology means that English RIs are actually ambiguous between an infinitive and a default finite form. This then is the basis for the explanation of various distributional differences, including the greater overall frequency of (apparent) RIs in English, and their comparative freedom to occur with subject noun phrases that are specified for number. Hoekstra and Hyams' overall conclusion concerning the difference between adult and child language is quite similar to Wexler's to the extent that they propose that a principal source of difference between child and adult grammars is difference in the interface of syntactic with extra-syntactic systems. However, their account does not rely on any syntactic constraint in child grammar that is absent from adult grammar; thus their approach is consistent with a stronger version of the continuity hypothesis discussed earlier. Both the chapters by Wexler and by Hoekstra and Hyams include analyses of accusative subjects in root clauses in child grammars. Radford's chapter is devoted to another case of non-nominative subjects in root clauses in English: this time apparently in the genitive case. The qualification is important, however: Radford's final conclusion is that there are no genuine genitive subjects in child English; rather, the forms that seem to correspond to genitives in adult grammars have a different status (or rather, different statuses) in child grammars. As Radford points out, analyses that have taken these subjects to be genitive and that have aimed to explain why such subjects occur in child language, despite their ungrammatically in adult grammars, have taken the phenomenon as crucial evidence for (differing) conclusions about the nature of child grammars. Thus, under some analyses, genitive subjects are possible in child grammars because these allow nominalisations as root clauses; under others because they allow root clauses with either under specified Infl or no Infl at all. Radford presents specific arguments against these analyses: if these 'genitives' are the subject of nominalisations - or of clauses with an underspecified or absent Infl - why is the verb sometimes inflected for agreement or tense? And how can interrogatives (with Subject-Aux inversion) also occur with 'genitive subjects'? If these subjects are always in nominalisations that involve a determiner with a VP complement, why can modals appear as well (since modals do not occur within VP)? If nonfinite clauses license genitive case on their subjects in child grammar, why is this not true of adult grammars, and how did the children acquire this pattern at all? Conversely, why are genitive subjects not more common in child grammars even when they are possible? Given these and other arguments against the specific analyses of 'genitive' subjects in child language, Radford concludes that they can be rejected essentially on empirical grounds. This is an important conclusion since he also argues that all of these analyses would entail that child grammars are significantly different from adult grammars. In contrast, the proposal that he puts forward entails a much higher degree of congruence between child and adult grammar; at least with respect to the phenomenon (or rather, in his view, phenomena) in question, the observed differences are due to changes in the acquirers' morphological and syntactic analysis of the pronouns themselves, rather than to differences in the constraints on clause structure.
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Most of the contributors to this book focus on the acquisition of a first language by children, although conclusions about maturational changes such as those drawn in Wexler's work clearly have implications for language learning by adults. Schwartz's topic, in contrast, is the acquisition of a second language. In particular, she addresses directly the question of whether L2 acquisition is different from LI acquisition, and if so, how the differences are to be accounted for. Schwartz adopts the position common to most contributors to this volume that LI acquisition is very heavily constrained by Universal Grammar. Since she also rejects the idea that L2 acquisition replicates exactly normal LI acquisition, and acknowledges results indicating that even the most successful adult L2 acquirers do not reach the same final states as speakers who acquired the language as children, a possible conclusion - and one that has frequently been drawn - is that adult learners do not have (full) access to UG, that their 'language instinct' has been 'dismantled'. However, Schwartz argues strongly against this conclusion. Instead she argues that the only difference that it is necessary to posit between LI and L2 acquirers is that their 'initial state' is different. In fact, Schwartz argues for the maximal difference between the initial states of LI and L2 acquirers. By assumption, for LI acquirers parameters of UG may only be set to default values if at all. In contrast, Schwartz argues that L2 acquirers transfer their knowledge of their first language in toto as their initial state for L2 acquisition. Further, Schwartz argues, this 'Full Transfer' is not determined by the age of the acquirer; even child L2 learners show evidence of this process. In reaching this conclusion, Schwartz reviews two other models of transfer and L2 acquisition and presents data arguing against them. The first model she discusses is the 'Minimal Trees' hypothesis, according to which lexical projections and their associated linear order transfer into the initial state of the L2, but functional categories do not; instead these are added progressively by lexical learning, in an order determined by their hierarchical position. Schwartz introduces data that support three arguments against this model: cases in which there is evidence for LI functional structure even in the earliest stages of L2 acquisition; cases where this structure persists at intermediate stages; and differences between LI and L2 acquirers that are unexpected under this model since the progressive addition of functional structure should be the same for both. The second model reviewed is the 'Weak Transfer' or 'Valueless Features' hypothesis, according to which both lexical and functional projections from the LI transfer, but the 'strength' of the features of functional heads - the engine of movement in the theory assumed - does not. Schwartz's argument against this model derives from cases in which there is transfer of LI orders that are assumed to derive from movement (and ultimately feature strength); these orders are not shown by L2 acquirers whose LI lacks the relevant movement. Finally, Schwartz explores in some detail the support for the 'Full Transfer/Full Access' model provided by Hulk's (1991) study of Dutch L2 acquirers of French. Although in other work Schwartz has argued for the 'Full Access (to UG)' (e.g. Schwartz and Sprouse, 1994), part of the model she espouses, in this chapter she concentrates most heavily on the argument for 'Full Transfer'; the argument stated
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here for 'Full Access' is essentially one of economy: given the demonstration that the initial states of LI and L2 acquirers are radically different, the onus is on those who propose a further difference between the two sets of acquirers (differential access to UG) to demonstrate the necessity of this additional distinction. The paper by Tesar and Smolensky deals with the problem of acquisition as it arises in Optimality Theory (OT). In OT, language variation is captured in the variety of priority rankings that can be given to a universal constraint set. Tesar and Smolensky argue that this structure, unlike, for example, the binary switches of Principles and Parameters theory, aids the language learner in finding the correct grammar. Consequently, the restricted linguistic evidence available to a child can rapidly distinguish the target grammar from the enormous number of alternatives. The authors also point out how this approach to learning escapes the traditional bugbear of language acquisition, Gold's theorem (see Gold, 1967), by making use of implicit negative evidence. Tesar and Smolensky analyse the learnability problem into two components: Robust Interpretative Parsing and Grammar Learning, and discuss how they are, both involved in their iterative model of language acquisition. The first step in this model consists of the computation of the hidden structure of overt input data. This computation is done by the parser, which is 'robust' because it has the capacity to use the learner's current grammar to assign a structural representation to forms that are deviant with respect to that grammar. As Tesar and Smolensky note, the requirement that such ungrammatical forms be parsed seems 'paradoxical'; input data count as information only if the current grammar (incorrectly) analyses them as ungrammatical. Unlike other models in which ungrammatical forms are unparsable, within OT input can be given an interpretative parse despite its ungrammaticality, and can thus be used to revise the grammar. This revision is the second step in the model, consisting of the gradual approximation to an optimal grammar (i.e. a language-specific ranking of constraints). Learning an optimal grammar crucially entails applying the grammatical constraints of OT, which are by hypothesis part of the learner's initial state, in order to deduce a harmonic ordering of structural descriptions. On the basis of such ordering, the learner iteratively revises the current constraint ranking so that constraints violated by the optimal candidate are demoted to be dominated by constraints violated by sub-optimal candidates: this is the Constraint Demotion algorithm. One particularly attractive aspect of OT is that it is amenable to exacting formal specifications, and researchers can develop explicit algorithms within the framework. This paper is no exception. The Constraint Demotion algorithm is the basis for their results on the complexity of acquisition; we know the ranking can be learned with only a number of informative examples quadratic in the number of constraints, because this level of performance is a provable consequence of Constraint Demotion. Jusczyk presents a cogent overview of some of the last decade's research into infant speech processing, demonstrating that methods such as the headturn technique can reveal the developmental course of sensitivities to different aspects of the speech stimulus before the infant produces any actual speech. This research underlines the
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importance of a developmental perspective on processing, as is clear from his discussion of research on speech segmentation. The speech signal is substantially redundant - as is appropriate for vulnerable information being transmitted over a noisy medium. It is often difficult if not impossible for studies using adult subjects, or computational studies of the information structure of large language corpora, to say anything about the relative priorities of the different types of intercorrelated information - prosodic, phonotactic and lexical - that provide adults with good cues as to where words might start and end in continuous speech. Some of the studies reported by Jusczyk show that sensitivity to these different segmentation cues develops at different points in infancy, and allows us to appreciate their interrelationships more fully. He suggests that prosodic information may be fundamental in establishing speech segmentation, and possibly also in the structuring of sequential information. In the course of his discussion, a fuller picture emerges of the temporal profile in which the developing infant establishes internal representations of segmental information, phonotactics, prosodic regularities, lexical entries, and even the distributional properties of function words. Further, experimentation using infants exposed to different ambient languages allows us to approach the issue of exactly what is universal in language acquisition. For instance, research by Cutler and her colleagues (see, e.g., Cutler and Norris, 1988; Otake et al., 1993) has revealed that the languages of the world seem to choose from only three different prosodic criteria for speech segmentation - moraic, syllabic and metrical - but crosslinguistic studies of development are necessary to establish the nature of the universal sensitivity to prosody that gives rise to one of these mutually exclusive alternatives. Overall, it is clear from the review and discussion in Jusczyk's chapter that the developing infant is exquisitely sensitive to the distributional structure of the ambient speech at various levels, but that some of these levels are particularly salient to the infant and seem to have developmental priority. The developmental profile may owe something to general cognitive development, such as the growth of resources for memory and attention, and to some extent specifically linguistic factors may be implicated. Outlining an approach to investigating the latter, Jusczyk ends with a description of current work aimed at testing particular implications of Optimality Theory for language development, presaging further interpenetration of two of the strands of acquisition research represented in this volume. Tinker's paper addresses a high-profile debate that has crossed over into all of the constituent disciplines in the field of language acquisition; it concerns the principles governing the acquisition and maintenance of regular and irregular lexical items. Rumelhart and McClelland (1986) made strong claims that Parallel Distributed Processing (POP) models are capable of exhibiting behaviour - specifically, involving the formation of the past-tense form of verbs - that had traditionally been interpreted in terms of the learning and deployment of linguistic rules. Since then, connectionists have seen pronunciation behaviour as a richer testbed for the same claim regarding symbolic versus subsymbolic processing, but the controversy regarding the modelling of the past-tense has continued, on the one hand with further investigation of the human data concerning morphological processing and with criticisms of twolayer network approaches (e.g., Pinker and Prince, 1988; Prasada and Pinker, 1993)
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and, on the other hand, with demonstrations of the abilities of more sophisticated connectionist and statistical approaches (e.g., Hahn et al., 1997; Hare et al., 1995). A new dimension to this argument is provided by Westermann (1997), who demonstrates some of the capabilities of connectionist networks that are allowed to grow new structure in the course of training, and are therefore distinguished from the more traditional networks in which the form of the architecture and of the inputs and outputs is given from the beginning. Pinker's paper marshals the evidence for the view that children develop both an associationistic and a rule-driven approach to past-tense formation, applying them respectively to irregular and regular inflection. Twelve sets of linguistic and psychological data are presented, some of them subcases of more general arguments. Pinker claims that these arguments all reinforce the distinction he makes between processing that draws on memory for irregular forms, and processing that utilises rules to produce regular inflections. As an example, compound forms may involve irregular but not regular plurals: 'mice-infested' is permissible, but not 'rats-infested', only 'rat-infested'. This observation is interpreted as evidence for a processor in which memorised forms (such as 'rat', but also including irregular forms such as 'mice') are input to a mechanism of complex word formation, with regular inflection (of the compound) being applied at the end of the process; in this process there is no opportunity for regular inflection to apply to 'rat'. In addition to such linguistic data, Pinker also considers behaviour such as the well-known overregularisations of irregular verbs - 'breaked' for 'broke'. Such overgeneralisations, Pinker argues, are produced by children not because they are 'regularity-imposers', but because they have not had enough experience of irregular verbs to feed the pattern-associator. Pinker also discusses data from patients suffering from disorders that differentially affect only the memory system, or only the grammatical system, such as anomic aphasia, Alzheimer's disease and Parkinson's disease. These data show that memory impairment affects only the production of irregular verbs, whereas grammar impairment disrupts only the production of regular forms, thus providing further support for the word/rule model he advances. The conclusion is that regular inflection is the default operation, which applies when an irregular form cannot be retrieved from memory. This assumption also explains why frequency is correlated with irregularity: commonly heard forms are easier to memorise. If an irregular verb becomes less frequent, at some point in the course of time it will be converted into a regular verb to which the regular rule can apply. Pinker concludes with a consideration of German, in which the numerical basis of 'regularity' differs widely from that found in English, and he further sustains his case for a dual-route approach to inflection: regular inflection can be generalised independently of frequency. Overall, Pinker's arguments represent a challenge to proponents of connectionist, 'single-route' models of the processing of inflectional morphology. Teun Hoekstra died shortly before this volume went to press. Despite his illness, he contributed at all stages to the development of this volume and to the original conference. In great sadness, we dedicate this collection to his memory.
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Pinker, S., 1984. Language learnability and language development. Cambridge, MA: Harvard University Press. Pinker, S. and Prince, A., 1988. On language and connectionism: Analysis of a parallel distributed processing model of language acquisition. Cognition 28, 73-193. Plunkett, K., 1995. Connectionist approaches to language acquisition. In: P. Fletcher and B. McWhinney (eds.), 36-72. Powers, S. and D. Lebeaux, 1998. More data on DP acquisition. In: N. Dittmar and Z. Penner (eds.), Issues in the theory of language acquisition, 37-76. Bern: Lang. Prince, A. and P. Smolensky, 1993. Optimality Theory: Constraint interaction in generative grammar. Technical Report RuCCS TR-2, Rutgers Center for Cognitive Science (to appear, MIT Press). Prasada, S. and S. Pinker, 1993. Generalization of regular and irregular morphological patterns. Language and Cognitive Processes 8, 1-56. Radford, A., 1990. Syntactic theory and the acquisition of English syntax. Oxford: Blackwell. Radford, A., 1996. Towards a structure-building model of acquisition. In: H. Clahsen (ed.), 43-90. Rizzi, L., 1994. Early null subjects and root null subjects. In: T. Hoekstra and B. Schwartz (eds.), 151-176. Robertson, D. and A. Sorace, in press. Losing the V2 constraint. To appear in: E. Klein and G. Martohardjono (eds.), The development of second language grammars: A generative approach. Amsterdam: Benjamins. Roeper, T. and E. Williams (eds.), 1987. Parameter setting. Dordrecht: Reidel. Rumelhart, D.E. and J.L. McClelland, 1986. On learning the past tense of English verbs. In: J. McClelland, D.E. Rumelhart and the PDF Research Group (eds.), Parallel Distributed Processing: Explorations in the microstructure of cognition. Volume 2: Psychological and biological models, 216-271. Cambridge, MA: MIT Press. Schiitze, C. and K. Wexler, 1996. Subject case licensing and English root infinitives. In: Proceedings of the 20th Boston University Conference on Language Development. Somerville, MA: Cascadilla. Schwartz, B. and R. Sprouse, 1994. Word order and nominative case in non-native language acquisition: A longitudinal study of (LI Turkish) German interlanguage. In: T. Hoekstra and B. Schwartz (eds.), 317-369. Smolensky, P., 1996. On the comprehension/production dilemma in child language. Linguistic Inquiry 27,720-731. Sorace, A., 1993. Incomplete vs divergent representations of unaccusativity in non-native grammars of Italian. Second Language Research 9, 22-48. Sorace, A., 1996. On gradience and optionality in non-native grammars. In: S. Epstein et al (eds.), 741-742. Sorace, A., 1998. Optionality in native and non-native grammars. Manuscript, University of Edinburgh. Tesar, B. and P. Smolensky, 1998. Learnability in Optimality Theory. Linguistic Inquiry 29, 229-268. Thomas, M., 1991. Universal grammar and the interpretation of reflexives in a second language. Language 67, 211-239. Towell, R. and R. Hawkins, 1994. Approaches to second language acquisition. Clevedon: Multilingual Matters. Vainikka, A., 1993/94. Case in the development of English syntax. Language Acquisition 3, 257-325. Valian, V., 1990. Logical and psychological constraints on the acquisition of syntax. In: L. Frazier and J. de Villiers (eds.), 119-146. Werker, J., 1993. Developmental changes in cross-language speech perception: Implications for cognitive models of speech processing. In: G.T.M. Altmann and R.C. Shillcock (eds.), Cognitive models of speech processing. The second Sperlonga meeting, 57-78. Hillsdale, NJ: Erlbaum. Westermann, G., 1997. A constructivist neural network learns the past tense of English verbs. In: A. Sorace, C. Heycock and R. Shillcock (eds.), Proceedings of the GALA '97 conference on language acquisition, 393-398. Edinburgh: University of Edinburgh. Wexler, K., 1994. Optional infinitives, head movement and the economy of derivations. In: D. Lightfoot and N. Hornstein (eds.), Verb movement, 305-350. Cambridge: Cambridge University Press. White, L., 1989. Universal grammar and second language acquisition. Amsterdam: Benjamins. White, L., 1996. Universal grammar and second language acquisition: Current trends and new directions. In: T.V. Bhatia and R. Ritchie (eds.), 85-120.
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Lingua ELSEVIER
Lingua 106 (1998) 23-79
Very early parameter setting and the unique checking constraint: A new explanation of the optional infinitive stage^ Ken Wexler* Department of Brain and Cognitive Science, Department of Linguistics and Philosophy. MIT E10-20, Cambridge, MA 02139, USA
Abstract This paper argues that the traditional view of experience-dependent properties (learned properties) of language as developing late and non-experience-dependent properties as developing early is in fact often wrong. Parameters are set correctly very early (Very Early Parameter-Setting) and properties of inflectional items are also learned very early. On the other hand, some universal properties of language emerge later, presumably under a genetically-driven maturational program. The Optional Infinitive(OI) Stage (Wexler, 1990, 1992, 1994) of grammatical development is explained by the AGR/TNS Omission Model (ATOM) of Schiitze and Wexler, (1996). This paper derives this model via a new proposal for a developmental constraint: the Unique Checking Constraint (UCC), which prevents a D-feature on DP from checking more than one D-feature on functional categories, thus forcing either AGR or TNS to be omitted. The Minimalist framework of Chomsky 1995 is assumed - in particular the assumption that a D-feature and not a case feature is the driving force for the Extended Projection Principle. With AGR and TNS both having a D-feature, UCC predicts that finite sentences will not converge. The model also predicts that subjects of OI's will raise to a higher functional projection, even when case is not assigned by INFL, thus solving a traditional problem in the theory of OI's. With natural assumptions on the nature of null-subject languages, the Null-Subjection/Optional Infinitive Correlation of Wexler (1996) is derived from the UCC — that OI's exist in early child language if and only if the adult grammar is not an INFL-licensed null-subject language. Thus the UCC is seen as a fundamental explanatory force for a range of phenomena in early child grammar. Moreover the child data provide strong evidence for the claim that a D-feature motivates the raising of the subject in UG, thus unifying child and adult grammar and demonstrating the usefulness of the investigation of child grammar in the study of UG. Key words: Optional infinitives; Syntactic development; Parameters; Minimalism; Agreement; Tense; Maturation of grammar ' My thanks to Carson Schiitze, whose extensive and insightful discussions have helped me a great deal, to two anonymous reviewers, who provided extremely detailed and useful critical commentary on relatively short notice, and to the editors. And to the community of OI researchers, who via their work and discussion have made this area such a pleasure to work in. * Phone +1 617 253 5797; Fax +1 617 253 9767; E-mail:
[email protected] 0024-3841/997$ - see font matter © 1999 Elsevier Science B.V. All rights reserved PII: 80024-3841(98)00029-1
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1. Introduction: Against late learning early emergence In this paper I would like to argue for a dramatically different view of linguistic development than is standard in almost every approach to language acquisition that I know. In particular, the standard view of grammatical development assumes, implicitly or explicitly, that the aspects of grammar that are learned are the ones to develop slowly, and that the aspects of grammar that are innate are present very early. Let's us call this view the 'Late Learning Early Emergence (LLEE)' Hypothesis, the idea being that properties of grammar that just 'emerge', i.e. are encoded in the genetic system underlying language, emerge early and that properties of grammar that are experience-dependent emerge late. LLEE is rather natural and plausible; after all, 'learning' is the kind of thing that takes time, the experience must actually occur, usually after birth, and there is no necessary reason that emergence should take a long time - if the genetic system underlying brain development is responsible for a particular development, why can't the development, the emergence, take place by birth? The LLEE view is so strong that, it seems to me, it is advocated or assumed by approaches that are radically different in other ways, for example, on the question of how much and what is innate (genetically encoded) in linguistic development. Almost nobody is a radical behaviorist in today's environment in which generative grammar has shown the complexity of language. But there is still a very strong school (e.g. Quartz and Sejnowski, 1997; Elman et al., 1996), carried over from former days, of those who believe that only 'general purpose' mechanisms are innate, whereas the view which attempts to encompass the results of linguistic theory and the true empirical situation of language development in human children tends to believe that particular aspects of grammar (UG) are genetically encoded, so as to explain why language is the way it is and why and how all normal children arrive at essentially the same grammar with experience that strongly underdetermines the particular nature of the grammar. Both 'general purpose' nativists (i.e. most 'psychological' theories) and 'specific domain' nativists believe in LLEE. That is, most approaches seem to believe that learning takes time and that aspects of language which are not learned (whether domain-specific or general) tend to emerge early. To take one important example, consider the question of the development of inflection. Very roughly speaking, inflection is the linguistic process whereby grammatical information is encoded in 'small' grammatical formatives and added to 'contentful' words. The standard view is that much of inflection appears late, and is often incorrect, and that the reason that it is late is because there is much to 'learn' about it. In fact, the standard view is that very young children 'talk funny' because they have not yet 'mastered' ('learned') inflection and its properties. Thus a child might say me going home instead of / am going home because the case 'inflection' on the subject pronoun has not been learned and the appropriate grammatical inflection called the 'auxiliary' has not been learned, and is therefore omitted. Syntactic parameters are another domain of variation where learning based on experience must operate. Thus on the LLEE view, we would expect parameters to be
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set relatively late in development, only after sufficient experience had been accumulated by the child. Such an expectation is behind, for example, Hyams' (1986) famous hypothesis that English-speaking children had 'mis-set' the null-subject parameter, thereby producing null subjects well into the twos and even threes. Similarly, in a non-linguistic-theory framework, Grimm (1993) claims that Germanspeaking children at an early age do not know the correct word order for major constituents, constructions which in a more linguistic-theoretic framework, would be related to syntactic parameters. Thus, whether from a linguistic theory or general psychology viewpoint, LLEE seems to have been the dominant assumption of students of language development. In this paper I will argue that LLEE is at best partially true and that it is often strongly wrong. In particular I will argue for the following two (roughly stated) hypotheses: (1) Very Early Parameter-Setting (VEPS) (Wexler, 1996): Basic parameters are set correctly at the earliest observable stages, that is, at least from the time that the child enters the two-word stage around 18 months of age. (2) Very Early Knowledge of Inflection (VEKI): At the earliest observable stage (from the time that the child enters the two-word stage around 18 months of age) the child knows the grammatical and phonological properties of many important inflectional elements in their language. Notice that (1) and (2) come close to being equivalent. Borer (1984) argued that syntactic parameters are to be interpreted not as properties of the grammar as a whole, but as properties of morphological and inflectional elements in the lexicon (and see Manzini and Wexler, 1985; Wexler and Manzini, 1987 for the related 'lexical parameterization hypothesis') and Fukui (1988) further suggested that the parameters are related to the 'functional' elements in the lexicon. On this view the properties of inflectional elements and properties of syntactic variation are essentially identical. For ease of exposition, we will maintain (1) and (2) as separate hypotheses, but it is worth remembering that they may turn out to be two slightly different ways of expressing the same hypothesis. Why do I mention the entry into the two-word stage as the point at which parameters and inflectional properties are known? Not because of any inherent connection between the two-word stage and parameters or inflection. Rather, because the evidence which shows us whether young children know parameters and/or inflection is only available when children begin to produce strings containing at least two words. Quite possibly - quite likely, in my estimation - children have set basic parameters (and learned inflectional properties) before the entry into the two-word stage - we just don't have any evidence at the current time which tells us whether this is true.1
1
Of course, further development of experimental techniques, for example the selective-looking paradigm, might provide evidence about this extremely early knowledge.
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In this paper I will give some for arguments for VEPS and VEKI. And I will argue against the universality of LLEE for inflectional development, that is, I will argue that certain aspects of morphosyntactic inflectional development emerge somewhat late, although they are not learned. Thus a certain amount of inflectional development unfolds over time according to a genetic blueprint. I will also demonstrate that the surface characteristics of this development can differ in different languages. This leads to what appears to be a conundrum: how can development be guided over time by a genetic blueprint and yet the effects of development look so different in different languages? The answer will be quite revealing, in my opinion: the genetic blueprint is the same for all children, across languages. But learning of inflectional material of course also has to take place, and the children learn this inflectional material very early, according to VEPS or VEKI. The learned parameters (inflectional properties) interacting with the innately unfolding aspects of inflection combine to create quite different surface effects in the development of different languages. Thus variation across time and across languages is neatly and precisely accounted for, as the precise interaction of genetically-specified grammatical growth and the effects of learning. Such a deep explanation of time and language variation is exactly what we should be hoping for in the study of grammatical development. There is another major theme of this paper. Namely, I want to illustrate the growing importance of the study of grammatical development in the theory of grammar. That is, I wish to show how the study of grammatical development leads to particular claims and evidence about the nature of Universal Grammar. I will concentrate on one important case - the syntactic motivation for the Extended Projection Principle, the fact that subjects raise out of the Verb Phrase. I will argue that developmental research and adult (standard 'linguistic theory') research converge on the same somewhat unexpected conclusion about this motivation, and that the developmental results are perhaps even clearer than the adult results, despite the EPP being central to the theory of syntax. Other cases touched upon will include which functional properties (AGR?) assign NOMinative case, what default case looks like in a language, etc. The evidence from developmental work that I touch on in this paper is directly relevant to these issues, and syntactic theory that ignores this evidence fails to capture what I consider to be crucial, even central, phenomena. To ignore the developmental results in the construction and testing of linguistic theory, in my opinion, would be to make an arbitrary decision about which phenomena are relevant, the kind of arbitrary decision, say, that structural/behavioral linguistics made when it ignored judgments of grammaticality. The empirical and theoretical material that I discuss in this paper involves the Optional Infinitive (OI) stage of linguistic development, and a large number of cross-linguistic properties associated with it. In this paper I develop a new theoretical analysis of this stage which captures what have been difficult phenomena to capture, including why certain languages don't go through the OI stage; the analysis also integrates the theory of the stage with current syntactic theory, especially concerning the status of the Extended Projection Principle. Thus I believe the theory presented here to be more empirically adequate than previous theories concerning the OI stage with respect to linguistic development and also to be better integrated
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with syntactic theory. The large amount of detailed empirical investigation of the OI stage cross-linguistically in the last decade has made far more specific theories possible, and current theoretical analysis shows the large boost to theory construction that has arisen from this empirical investigation. 7.7. Summary of paper In the next section I briefly outline some of the central properties of the OI stage without providing any kind of detailed coverage. Section 3 discusses Very Early Parameter-Setting (VEPS) and some of the evidence for it. Section 4 draws some important consequences of VEPS for the theory of learning, in particular that parameter-setting must be some kind of perceptual learning. In Section 5 I discuss the evidence that the null-subject parameter is set correctly at the earliest observed stage. This is important for VEPS because the null-subject parameter has been classic case of a mis-set parameter, contrary to VEPS. Section 6 briefly draws implications about the incorrectness of Late Learning Early Emergence from the results in the earlier sections. In Section 7 I apply the same ideas to the study of inflection and make the case for extremely young children as 'little inflection machines' as opposed to the traditional view that they are poor at inflectional learning. Section 8 briefly describes the Schutze and Wexler (1996a,b) AGR/TNS Omission Model (ATOM) of the OI stage, which is the starting point I take for the investigation. In Section 9 I discuss the central question of why subjects of OI's raise, given that they are often not assigned case by non-finite INFL, relating the developmental results to the current Minimalist view of the Extended Projection Principle. Section 10 summarizes briefly the literature on cross-linguistic variation in which languages undergo the OI stage, the generalization being the Null-Subject/Optional Infinitive Correlation of Wexler (1996). In Section 11 I propose a new theory of the OI stage, which assumes that OI children are governed by the genetically-specified (and withering away in time) Unique Checking Constraint (UCC), which allows a D-feature on the subject to only check once. The UCC theory is integrated with the current view on the EPP, and provides a good deal of evidence for it. Section 12 shows how the central cross-linguistic variation phenomenon in the OI stage, the NS/OI, strictly follows from the UCC analysis of the previous section. In Section 13 I conclude, allowing myself some thoughts on the relation between linguistics and psycholinguistics, namely that it is now more clear in practice that it is important to integrate them, the developmental research being important in detail for the nature of human language. 2. The OI stage in grammatical development The foundations of the evidence for VEPS and VEKI came with the discovery (Wexler, 1990, 1992, 1994).2 of the Optional Infinitive (OI) stage in grammatical development. Wexler (1994) characterizes this stage as in (3): :
From now on, reference to 'Wexler, 1990, 1992, 1994' will be designated as 'Wexler, 1990ff.'
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(3) The Optional Infinitive(OI) stage (Wexler, 1990ff.) a. Root infinitives are possible grammatical sentences for children in this stage (around 2 years) b. These infinitives coexist with finite forms c. The children nevertheless know the relevant grammatical Principles, e.g. head movement, checking, etc. Since the existence of the OI stage with its general properties as described by Wexler in (3) are by now well-known and generally agreed to, I won't enter into detail about it. For illustration, let me just give one example that Wexler used to describe the OI stage, from Poeppel and Wexler, 1993. (4) shows the data (number of utterances of a particular type) as analyzed in Poeppel and Wexler, from one child Andreas at 2; 1. (original data from Wagner, 1985). (4) German, Poeppel and Wexler (19933) +Finite -Finite V2/not final 197 6 V final/not V2 11 37 German is an SOV/V2 language. SOV means that its underlying constituents, according to the standardly assumed mechanics for German, are in the order Subject Object Verb. That German is V2 (Verb Second) means that in root (matrix) clauses, the finite verb moves to second position (the head C of the Complementizer Phrase (CP)) while another constituent occupies first position, the Specifier of CP). Thus Wexler argued that it follows from the properties of the OI stage in (3) that German-speaking children in the OI stage should produce finite verbs in second position and non-finite verbs in final position. The data in (4) strongly conform to this prediction. Finite verbs (as determined by their visible inflectional morphology) occur in second position and non-finite root verbs4 (as determined by their visible inflectional morphology) occur in final position. Wexler also argued that the OI stage could be demonstrated in other languages when processes other than V2 (V to C movement) distinguished finite from non-finite verbs. For example, in languages (such as French) which have (finite) verb raising to INFL, the properties of the OI stage in (3) argue that the finite verb will precede certain adverbs or other elements (e.g. negation) whereas non-finite verbs (which don't raise) will follow these elements. Thus, on the basis of a variety of grammatical processes cross-linguistically, Wexler argued that the OI stage properties in (3) characterize child grammars across many languages. In light of previous research on child language, the demonstration that the OI stage existed across languages is a surprising result, since the non-finite stage posited was independent of the particular grammatical process which showed it (e.g. 3
See e.g. Mills, 1985; Weissenborn, 1991; Clahsen et al., 1994; Boseret al., 1992; Behrens, 1993 for data which fits the same analysis. 4 The root verbs are 'main' verbs, verbs that should be finite in the adult grammar.
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V2 versus V to INFL) but seemed to have an independent existence. Of course, from the standpoint of explanatory adequacy in linguistic development (as explanatory adequacy is understood, for example, in principle-based syntactic theory) the result was a clear advance, since it seemed principle-based rather than construction-specific. By now, the existence of the OI stage in many different languages has been so well-documented that its existence and general properties are no longer controversial, though many important details remain to be explicated, and the theoretical basis for the OI stage is subject to active investigation. With this brief background, I will discuss the relevance of the OI stage to the question of VEPS and VEKI, and then go on to the study of cross-linguistic variation in the OI stage and a deeper understanding of the stage itself. 3. Very early parameter-setting As early as Wexler (1990, 1994), it was argued that work on the OI stage had shown that children had set parameters correctly at an extremely early age. Wexler (1996) formalized this observation as VEPS, presented in (5): (5) Very Early Parameter Setting (VEPS) Basic parameters of verb movement, e.g. V to I, V to I to C, are correctly set at the earliest observed stages, thus in the OI stage they're correctly set. Parameters that are set at the earliest observed stage (i.e. at beginning of production of multiple word combinations, around 1;6) include: a. Word order, e.g. VO versus OV (e.g. Swedish vs. German) b. V to I or not (e.g. French versus English) c. V2 or not (e.g. German versus French or English) d. Null subject or not (e.g. Italian versus English or French) This is not the place to discuss the evidence for (5) in any detail. To briefly review, one can find evidence for (5a) by observing OI's in, say, Swedish and German. These root infinitives will appear in sentence final position in German, but in Swedish they will appear after the subject and before, say, the object. That is, the OI's, not undergoing V2, will appear in their base-generated position. Wexler (1990, 1994) documents these differences, based on data in Plunkett and Stromqvist (1990), and Platzack (1990). Or, one may observe Japanese in its early state, where there is no verb movement, and notice that the verb is in final position, after objects, that is early Japanese shows SOV, not SVO. English, whose main verbs do not undergo verb movement, shows mostly SVO order, even for finite verbs. Thus the correct word order is displayed quite early, whether SVO or SOV. Similarly, the raising of finite verbs in French means that the finite verb will precede negative pas and the non-finite verb will follow pas, and this is demonstrated by Pierce (1989, 1992) for very young French children. English main verbs do not raise and thus finite verbs should follow negation not in young children, which they
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mostly do - there is no evidence that sentences like she likes not ice cream are systematically created by young English-speaking children. Thus (5b) holds, the value of the verb-raising parameter is set extremely early, whether its value is raise or not raise. The verb-second parameter in (5c) is also set correct at the earliest ages, as Wexler argued. The data from Poeppel and Wexler 1993 that we have already discussed shows that German children have V2 for finite verbs at early ages - the finite verb appears in second position but the non-finite verb appears in final position. Similarly as Wexler demonstrates, in the Mainland Scandinavian languages (Danish, Norwegian, Swedish), which are V2/SVO, the finite verb precedes negation (because the verb has raised over it, to C), whereas the root infinitival remains to the right of negation. Thus these languages show V2 at very young ages. On the other hand, negation precedes the verb in young English-speaking children, showing that they do not raise the verb, even the finite verb, to C. French children, on the other hand, since French is a verb raising language, will have the finite verb precede negative pas. But we can see that these children are not speaking a V2 language because they will not in general produce constituents other than the subject (objects, adverbs, etc.) in first position, with the finite verb in second position. German-speaking children, on the other hand, will do just this (Poeppel and Wexler, 1993), thus showing that German, but not French, is a V2 language at very early ages. The above arguments can be repeated, for many different languages and many different construction types, but without going into detail here they should give the flavor of the arguments for VEPS; namely, for both values of these (binary) parameters, if a language exhibits a certain value of the parameter, then a child learning that language has set the parameter for that language from the earliest observations that we can make. In particular, since most of the arguments involve the correlation between word order and morphology on a verb, we need to observe at least one verb and one other constituent in a sentence in order to test whether a child has set the parameter correctly (for example knows that the verb raises to INFL or not, or raises to C or not). Thus, minimally the child must be in what has been called the two word stage, since we must observe at least two words in an utterance, the verb and at least one word for another constituent. If all utterances only contain one word, no observations on parameter-setting can be made from natural production data. In English it is standardly said that the child enters the two word stage at about 18 months of age. As far as I can tell the observations that I have made above concerning the parameters in (5) hold from the very beginning of the two word stage; that is the source for my estimate that the child has set the parameters correctly by approximately 18 months of age. Of course, we don't know how much before entering the two word stage the child has actually set the parameters correctly. This age is an upper bound on the age of correct parameter-setting; for all we know the child has set the parameters correctly by age 1;0 or even earlier. It will take the development of further experimental methods (e.g. selective looking paradigms or other methods for studying infant cognition) to determine more precisely the age at which children set basic parameters correctly.
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Nevertheless the extremely early upper bound that we have determined is quite important. To the extent that VEPS is correct (and the overwhelming weight of evidence is in favor of VEPS, at least for basic parameters of clause structure and syntax), we know that the child has set parameters correctly before entering the two word stage, thus the child has set parameters correctly before using them. 4. On the theory of learning This result (VEPS) thus has two extremely important consequences for the theory of learning. First, it makes even more strikingly clear the hypothesis (Wexler and Hamburger, 1973, and many references since) that children do not use what Wexler and Hamburger called negative evidence in language acquisition. In particular, children do not learn from corrections by adults of their utterances. Wexler and Hamburger drew this conclusion on the basis of evidence from Brown and Hanlon (1970) that showed that adults do not correct (or understand) ungrammatical utterances by young children more than they correct (or understand) grammatical utterances. Wexler and Hamburger concluded that the lack of negative evidence made even more necessary the conclusion that there must be innate specification of some linguistic structures, a conclusion since widely (but not universally) adopted. But VEPS provides an even stronger result. Namely, if VEPS is true, then children have learned the correct values of parameters before they illustrate these values in their productions. Thus it is logically impossible for them to have used negative information as part of the evidence for setting parameters. The only way for adults to provide negative information to the children would be for the adults to read the minds of the children. On the assumption that adults can't read the minds of children to know what parameters the children have instantiated in the absence of productions by the children instantiating the parameters, we can conclude that children cannot have used negative information to set the parameters. Thus for one class of linguistic expertise which is uncontroversially 'learned' (the values of basic parameters of clause structure and inflection), we know that negative information is not used by the children. The second important consequence of VEPS for the theory of learning involves the nature of learning itself. Since children have set the parameters correctly before instantiating these values in productions (i.e. they have set the parameters by the end of the one word stage), the children have learned the parameter-settings without making responses which involve the parameters. We can say that the learning of parameters is a kind of perceptual learning, since it is done perceptually, rather than behaviorally. Perceptual learning is an old and important topic in psychology; there has been no doubt that it goes on, say, in visual perception, where the system under investigation is only an input system and not also an output system. Following VEPS, it is now clear that perceptual learning is also the basis for the setting of linguistic parameters.3 This is a nice generalization over cognitive domains, and shouldn't really be surprising, though it is perhaps not often stated as a general conclusion. 5
The kinds of learning theories that would thus be ruled out by VEPS (for basic parameter-setting at least) would include, for example, ideas based on Piaget's theories, which demand for higher cognitive functions that learning strongly depends on a motor response.
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A natural questions arises: is this empirical consequence of VEPS theoretically reasonable? That is, are there possible learning theories for parameters which don't involve correction or responses by children? Can perceptual learning actually work for parameter-setting? In fact, the most worked-out theories of parameter-setting turn out to be theories which treat parameter-setting as a kind of perceptual learning. Consider, for example, the 'learning on errors' approach to learning grammatical properties (Wexler and Culicover, 1980) specialized to parameter-setting in a Principles and Parameters framework in Gibson and Wexler (1993). The assumption is that the learner attempts to generate an input sentence with her current grammar (i.e. parameter-settings) and if she can't generate it, she changes the setting of a parameter. No behavioral response by the learner is assumed - it is a type of perceptual learning. The same can be said for other approaches to parameter-setting, such as Dresher and Kaye's (1990) 'cue-based' approach to phonological parameter-setting. Thus perceptual learning of parameters is in fact a potentially viable theory, and is implemented and worked out far more than an approach which assumes that the child must respond behaviorally in order to learn. Thus the theory of learning and the empirical properties of grammatical development as captured by VEPS seem to converge on perceptual learning as the correct model for grammatical development.6 5. The early setting of the null-subject parameter Of the parameters used to illustrate VEPS, we have not yet discussed (5d), the null-subject parameter. It may surprise the reader that I have claimed that the nullsubject parameter is set correctly at the earliest observed ages because there is a famous result in language acquisition due to Hyams (1986), which says that Englishspeaking children mis-set the null-subject parameter for a fairly long period, incorrectly setting the parameter as yes, that is, allowing null-subjects, as instantiated by sentences like baking cookies. In fact, there are a large number of languages which have been studied at early ages, and children speaking these languages all seem to allow null-subjects even if the adult language does not (e.g. French, as in Pierce, 1989). Given these empirical results, it is quite clear that children at young ages allow null-subjects. But in my original paper on the OI stage (Wexler, 1990ff.), I sug6
Of course there is a kind of 'implicit' response in the models of parameter-setting. For example, in Wexler and Culicover's (1980) or Gibson and Wexler's (1993) approach, the learner attempts to generate the input sentence (covertly) to see if it can be generated by the current grammar. But this covert response is quite different from what is meant by theories such as Piaget's, which assume that a behavioral response must be made. The parameter-setting theories involve cognitive not behavioral processes. In order for an adult to 'correct' (provide 'negative information to') the language learner, the adult would have to be able to observe the cognitive processes, clearly an impossibility if one assumes that this type of rather interesting extrasensory perception does not exist. For a discussion of the need for extrasensory perception in earlier behavioral ('stimulus-response') models of language learning, see Batchelder and Wexler (1979).
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gested the possibility that children produce these null-subjects as the result of the OI stage. The basic empirical result that I suggested might hold, and that has been documented in many places since7 is that during the OI stage, Optional Infinitives (i.e. non-finite main verbs) have a far greater proportion of null-subjects than do finite main verbs. Basically, across (non-null-subject) languages, differences in the rate of null-subjects contingent on the verbal inflection often emerge on the order of 70-95% null subjects with OI's (nonfinite main verbs) and 15-30% null subjects with finite verbs. Given this result, Wexler (1996) (see also Bromberg and Wexler, 1995) suggested that the null-subject parameter is not mis-set by young children; rather, the null-subjects of OI's are licensed in some way by the non-finite main verb, the null-subject perhaps being PRO, which is licensed in non-finite contexts (e.g. as the subject of control verbs: Mary triedfPRO to leave). Schiitze and Wexler (1996a,b), suggested in particular that -TNS (as opposed to -AGR) licenses PRO. There are many theories about how null-subjects are licensed by OI's, and they do not all assume that the subject of an OI is PRO. I will not review these theories here. But all these theories do have in common that null subjects are allowed because of the existence of the OI in the sentence. Thus the null-subject parameter has not been 'mis-set'. Rather the null subjects are licensed by the non-finite verb. However, the empirical results show that even finite verbs in non-null-subject languages allow null-subjects in young children, though at a greatly reduced rate. How can these be explained if it is OI's that license the null-subject? Don't we need to assume still that children have mis-set the null-subject parameter as yes? Again, there are a number of ideas concerning these null-subjects of finite verbs. Let me, following Bromberg and Wexler (1995), propose that these null-subjects are a kind of topic-drop* That is, the null-subjects of finite verbs represent a kind of pragmatic error. These languages sometimes drop particular kinds of topics as in (7) in English: (7) a. Speaker one: John will never lose weight. He's eating too much, b. Speaker two: Yeah, isn't exercising enough either. In (7b) the second speaker drops a very clear subject topic: John. Subjects that are such strong topics that they will be quite destressed in English are candidates for topic-drop. If speaker two had used a subject, it would have been a highly destressed he. What I am proposing is that children sometimes drop topics even in situations where they should not and that the excess null-subjects of finite verbs in young children are the result of a kind of pragmatic error, one in which the children treat information that is not a very strong topic nevertheless as a strong topic, one strong 7
See Phillips (1995a,b) and Razzetti (1996) for a summary of data from many languages Hyams and Wexler (1993) suggested that children using null-subjects in non-null-subject languages might be doing a kind of topic drop, but they didn't suggest that this was particularly true for null-subjects of finite verbs. 8
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enough to be omitted.9 Such a proposal is quite consistent with a large body of empirical evidence which suggests that children treat new information as old information, but not the other way around, what Thornton and Wexler (in press) call Asymmetry. For example, as Avrutin and Wexler (1992) and Avrutin (1995) have pointed out, Karmiloff-Smith's (1981) results that show that young children use definite instead of indefinite articles (but not the other way around) and that they use pronouns when lexical NP's are needed means that they treat new information as old information. As Thornton and Wexler argue, following the approach of, but slightly modifying, Chien and Wexler (1990), this suggests that children assume that a discourse element is available to listeners even when it isn't. This is a kind of pragmatic error - children don't understand well enough what listeners know about a discourse, and assume that they know more than they in fact know. The converse doesn't seem to happen. In fact, it may turn out that topic-drop is not quite the right way to look at the phenomenon in adults; rather, it may be that the null subject in English is an optional spell-out for destressed subject pronouns.10 This would explain the possibility of dropping expletive subjects, which are typically destressed - see footnote 5. Referential subjects are destressed when they are very strong topics; as I pointed out, if a subject were used in (7b) it would be a destressed he. Very strong topics are destressed; thus if children mistakenly assume that certain referential subjects are very strong topics, they will consider them destressed and thus candidates for spell9
Haegeman (1995) has argued that the null-subjects of finite verbs cannot be (all) topic-drop because non-topics are often dropped by children, e.g. expletive subjects, and she has provided empirical evidence of this dropping of expletive subjects. To the extent that this result is correct, I agree that topicdrop cannot be a full explanation. Rizzi (1994a,b) has proposed that the dropped subjects meet the condition of diary drop (Haegeman, 1990) and that these diary drop null subjects result from a quite complicated syntax - they are a null constant and licensed by some complicated conditions so that only specifiers of roots may be null-constant. However, so far as I can tell, Rizzi's theory does not predict the strong difference in rates of null-subjects for finite verbs and for OI's. Furthermore, it mispredicts the wh null-subject data that I will soon discuss. But it is fair to say that if expletive null-subjects of finite verbs are a real phenomenon, they can't be captured by the topic-drop theory. So far, however, expletive nullsubjects have only been observed in very few languages, and not very extensively. Moreover, it is possible that in at least some (perhaps all) cases, the expletive subject is a quasi-argument (it rains), at least for the child, so that topic-drop can explain these null subjects (e rains, if it exists in some language). It's not clear how many non-quasi-argument null-subjects exist, forms equivalent to the English e seems that Mary has left. Hyams (1986) claims that in the null-subject stage expletives aren't used - could it be that non-null and null expletives as well aren't used? This is possible, as young children seem to prefer verbs with argument subjects, perhaps as a result of a constraint against A-chains or perhaps instead of a constraint against A-chains (Borer and Wexler, 1987, 1992; Babyonyshev et al., 1994, 1998) At any rate, the case of null and non-null subject expletives remains as a major case for investigation in young children's grammars. It should also be mentioned that in more recent work Haegeman (p.c.) reports that null subjects are indeed possible in embedded clauses in the diary-drop register. Thus it appears that the specifier of root analysis in fact doesn't account for diary-drop in the same way that truncation doesn't account for OI structures - embedded clauses are not oblivious to the process. 10 Only distressed subjects in first position can alternate with a null subject, (i) Speaker 1: John is buying a book. Speaker 2: What is he/*e buying'.'/What's he/*e buying The subject can't be dropped by Speaker 2 because it is not in first position.
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out with a null-subject. From now on I will simply talk about topic-drop, since we are dealing only with referential subjects, but the alternative possibility should be kept in mind. Thus if children assume that some subjects are very strong topics, strong enough to be dropped, this is congruent with the general point that children assume that the listener knows more about the subject than she (the listener) actually does. Let's say: (8) In a language, Topic-drop applies to Very Strong (VS) Topics where we will not specify the conditions which make a topic VS. We also assume: (9) Children believe that some non-VS subjects are in fact VS ( a pragmatic error). From (8)-(9) it follows that children will drop subjects of finite verbs even when they shouldn't. Let me mention just one further piece of evidence for (9). In some V2 languages, for example, Dutch, topics in Spec, C can often be dropped (the stronger they are as topics, the more readily they can be dropped - there is clearly a pragmatic effect). Children do this topic drop from a very early age (e.g. Van Kampen, 1997). Wexler et al. (1998), studying a large number of Dutch children, showed that the children dropped topics more often than would be expected by adults, in conformity to (9). Thus I assume two processes that allow null-subjects in children in the OI stage. (10) In OI stage, null-subjects are: a. PRO or Topic-drop if the verb is non-finite (an OI) b. Topic drop if the verb is finite That is, dropped topics aren't licensed by inflectional material on the verb, or particular inflectional projections existing or missing. So they can exist with finite or nonfinite (OI) main verbs. On the other hand, PRO is grammatically licensed by OI's. Thus the conditions under which OI's may have null subjects (topic drop, or OIlicensed) properly include the conditions under which finite verbs may have null subjects (topic drop). Thus (10) predicts: (11) The rate of null-subjects with OI's is larger than the rate of null-subjects with finite main verbs. As we have already discussed, (11) is true, so the two-process theory in (10) predicts the empirical results across a wide variety of languages. Of course we even know that often the rate of null-subjects for OI's is much greater than the rate for finite verbs. This simply suggests that the pragmatic error (9) is not extremely common - just common enough to allow a certain rate of null-subjects of finite verbs. Moreover, it often happens that the rate of null-subjects in some languages for OI's approaches 100% (though not in all children in all languages). This large rate of null-subjects for OI's suggests strongly that the non-finite nature of the OI gram-
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matically licenses the null-subject. This is a very different phenomenon than the low rate of pragmatic-error-induced null-subjects for finite verbs. The two-process theory of null-subjects allows us to explain the strongly differential rate of null-subjects in finite and OI sentences. However, it makes an even stronger prediction, as argued in Bromberg and Wexler (1995). Consider wh-sentences, where the wh is a non-subject, say an object or an adjunct. We can ask whether the subject can be null. Let's take as an example an adjunct question, with a locative question, where in English. First, suppose that the verb is finite. This means that PRO is not licensed, thus structure (12b) is ungrammatical. That is, only (lOb) Topic Drop is the potential source for a null subject. Let us designate a null topic as e(T), as in (12c). But we have already indicated (see footnote 7) that only topics in first position can be omitted, and children know this.11 Thus (12c) is ungrammatical for children. (12) a. b. c. d. e. f.
where is she going? * where is PRO going? * where is e(T) going? where she going? where PRO going? * where e(T) going?
Now consider OI wh questions, as in (12d), where the verb is non-finite. By (lOa), the OI licenses PRO, so that (12e) is grammatical. As with the finite verb, the subject not in first position cannot be dropped as a topic (or, following Bromberg and Wexler, 1995, topic drop applies only to topics in Spec,C and there is already an element in Spec,C, the wh-element where.). Thus (12f) is ungrammatical. The analyses in (12) yield the predictions of the following sentence patterns in OI grammar. (13) a. b. c. d.
where is she going? * where is e going? where she going? where e going?
The prediction from the two-process theory thus is that for wh-questions, the subject may be omitted for OI's, but not for finite verbs. The reason is that for finite verbs the subject can't be PRO and for wh-questions topic-drop of the subject isn't allowed. Bromberg and Wexler (1995; cf. also Roeper and Rohrbacher, 1995) showed that in fact this empirical result strongly follows. The data in (14) is from 11
Bromberg and Wexler (1995) argued that topic drop couldn't take place finite in wh-sentences like (12c) because topics have to be in Spec,C and the wh constituent already fills Spec,C in (12c) so that the topic cannot fill Spec,C. This is quite possibly the correct explanation. I have talked about 'first position' only in order to generalize to adult forms in which expletives drop and also forms like (7b), where the dropped subject is probably not in Spec,C. If these forms are accounted for in some other way, then the Spec,C analysis will be preferred.
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one child studied by Bromberg and Wexler (1995); the child is Adam, reported on in (Which publication??, 1973). The data was taken from the CHILDES data base.12 (14) Finiteness of null and pronominal subjects in adam's w/z-questions Finite Nonfinite Null 2 118 Pronominal 117 131 The result in (14) is extremely strong. In wh-questions, Adam has plenty of pronominal subjects in both finite (13a) and non-finite (OI) (13c) sentences, and plenty of null subjects in nonfinite (OI) (13d) sentences, but essentially no null-subjects in finite sentences (13b). This is exactly the pattern that the two-process theory predicts in (13). Bromberg and Wexler studied other children and obtained the same result. They also obtained the same result considering all visible subjects, not just pronominal subjects; that is, in wh-questions, non-pronominal lexical subjects appear both with finite and non-finite verbs although the null-subjects appear only with nonfinite verbs. (They argued that pronominal subjects may be the best to compare to null subjects, because only a pronominal subject has the capacity to be topic-dropped, on pragmatic grounds.) The strikingly strong data in (14) (and for other children) is clear enough that it must be explained by any theory of the OI stage. As far as I know, other theories cannot explain this data. For example, Rizzi's (1994a,b) 'truncation' theory assumes that if a functional projection is present in the child's representation, then all projections underneath that projection are also present. Thus if there is a wh-question, CP must be present, and thus the empty subject, wherever it is, is in a projection under CP, and thus is not a Specifier of a root. Thus, as Rizzi argues, the truncation theory predicts that in a wh-sentence, with the wh-phrase in root position, since the subject is a non-root, it can not be null. Thus the 118 subjects of nonfinite verbs are impossible. Thus the truncation theory mispredicts the data. Of course we already know that the truncation theory cannot explain the difference in null-subject rates between finite and non-finite (OI) main verbs. Furthermore, the truncation theory predicts that OI's will not exist in wh-questions, since if CP exists TP (Tense-Phrase) must exist, on the assumptions of the truncation theory. Thus the very existence of non-finite wh-questions is evidence against the truncation theory, as first pointed out by Roeper and Rohrbacher (1995) and confirmed by Bromberg and Wexler (1995). The interaction of finiteness and null-subjects thus gives three empirical arguments against the truncation theory. It is true that there are very few OI's in wh-questions in languages like German and Dutch, unlike English or in fact, as Poeppel and Wexler (1993) showed for German (see now Santelmann, 1995, for Swedish), there are extremely few OI's when there is any constituent in Spec,C. Following Poeppel and Wexler (1993), we can see All references to the CHILDES data base are to McWhinney and Snow (1985).
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why this should hold. These are V2 languages. It is a property of V2 languages that if Spec,CP is filled by some constituent then C must be filled by a finite verb. Given VEPS, a child in the OI stage will have correctly set the V2 parameter (and Poeppel and Wexler produced extensive evidence for this in the German child they studied). On the assumption that a child who knows that a language is V2 knows the properties that UG says follow from the V2 nature of the language, however these are specified, we would expect that a child speaking a V2 language would insist that C be filled when wh or any other constituent filled Spec,C. But since it is also a property of such languages that only finite verbs can move to C, the child will fill C with a finite verb. Thus VEPS predicts that there are no wh-OI's in V2 languages. It is a virtue of an INFL-omission model such as Wexler (1990ff.) or Schutze and Wexler (1996a,b) that it predicts that wh OI's will exist in language like English but not in V2 languages like German, Dutch or Swedish. The truncation theory on the other hand mispredicts the possibility of wh OI's in languages like English.13 The basic problem with truncation is that it necessarily omits far too many functional projections. Once a category is missing, all higher categories must be missing. This radical and obligatory omission of categories simply doesn't appear to be a property of the OI stage, as much empirical analysis has shown. Of course, one could modify truncation so that the omission of these categories wasn't obligatory. But then the model would lose its 'truncation' characteristics and become (almost?) identical to the INFL-omission model of Wexler for which it was supposed to provide an alternative. The truncation theory has proved to be very valuable in showing what one kind of precisely specified reasonable alternative to INFL-omission would look like, so that precise predictions of INFL-omission versus an alternative could be studied. It will be very useful to continue to have a variety of models which meet the central phenomena but which make divergent predictions concerning other phenomena. Furthermore, the data in (14) cannot be explained by any theory which assumes that subjects are dropped only for informational reasons, i.e. only as a kind of pragmatic error (e.g. Greenfield, 1991). For why should there be a difference in this kind of subject drop for finite and non-finite verbs? Moreover, the data in (14) cannot be explained by a 'memory load' type theory which assumes that children drop subjects when the rest of the sentence (the verb phrase) is too long (e.g. Bloom, 1990). For, as Bromberg and Wexler (1995) pointed out, the memory load theory predicts that finite sentences, having 'longer' verb phrases than non-finite sentences,14 should omit subjects more often than non-finite n Crisma (1997) argues that there are no wh-OI's in French, a non-V2 language, in conformity with truncation, and against the INFL-omission model. But Phillips (1995 a,b) shows that almost all of the wh sentences in Crisma's data involve a (finite) auxiliary and noting that (Wexler, 1990, 1994) auxiliaries are never OI's, argues that we would expect Crisma's results independently of truncation. Thus the empirical results to date are compatible with INFL-Omission but not with truncation. Of course, it would be useful to have data on the question of whether wh OI's exist in other non-V2 languages, besides English. 14 This is automatically true if one counts length by morphemes, since Tense/Inflection counts as a morpheme, and it is even true if one counts length by words, since finite auxiliaries are often missing in OI sentences.
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sentences. This prediction should hold both for declarative sentences (where we already know it is a misprediction, since finite declarative sentences have in general far fewer null subjects than OI sentences) and for wh-questions (where we know it is a very strong misprediction, by data like (14)). Importantly, the two-process theory, so strongly upheld by (14), assumes that English-speaking children in the OI stage have correctly set the null-subject parameter, to the value no, null-subjects are not allowed. For if the children had set the parameter to yes, the theory would have made different predictions; namely finite wh-questions would have easily allowed null-subjects (i.e. (13b) would be grammatical). Thus, as Bromberg and Wexler (1995) argued, (14) is quite strong evidence that English-speaking children have set the null-subject parameter correctly to no. Furthermore, the equivalent of (13b) in a real null-subject language (e.g. Italian) is perfect grammatical, as expected. There is nothing about wh-questions which disallows null-subjects. Moreover, Rizzi (1994b) provides preliminary, suggestive evidence that young Italian-speaking children omit subjects of finite verbs in a whquestion (i.e. the equivalent of 13b). If this result is indeed true, then we can conclude that young Italian-speaking know that they are speaking a null-subject language.15 This rather precise and beautiful pattern of results, concerning the non-existence of null-subjects in finite object and adjunct wh-questions in a non-null-subject language (and their existence in a null-subject language), thus provides the strongest evidence, in my opinion, that the null-subject parameter is correctly set at the earliest observed ages: both for non-null-subject languages like English (where it is set to no) and to null-subject languages like Italian (where it is set to yes.) Thus we can conclude (as it seems to me by now the field already has, including Hyams (see Sano and Hyams, 1994) that the null-subject parameter is set correctly from the earliest ages. And that it is correctly set for both plus and minus values of the V2 parameter, depending on the input language. Thus the null-subject parameter (5d) can be added to the list of parameters set correctly at the earliest observed stages, providing further support for VEPS. In fact, to my knowledge, while there is extensive evidence (some of which I have just briefly reviewed) demonstrating the correct setting from the earliest observed ages of many basic parameters of clausal syntax, verb movement and inflection, there is almost no evidence demonstrating the incorrect setting of any parameter. For example, I know of no evidence showing that a child has incorrectly set the V2 parameter in German as not V2 or in French as V2. The lists of parameters and languages for which this conclusion holds is fairly large, and it grows every time somebody studies a new construction which shows parametric variation.16 15 Also suggestive in this regard are the results of Valian (1991), which suggest that there are a larger proportion of null-subjects in young Italian children than young English-speaking children, though the issue is somewhat complicated since we expect a good proportion of null-subjects in OI's, which English-speaking children have. 16 The strongest evidence of which I am aware which at first appears to show that a parameter has been mis-set is in Schoenenberger (1998) which offers quite convincing evidence that two young Swiss German-speaking children systematically produce embedded V2 constructions, while the adult language
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6. Early learning, growing principles That there is no evidence for the incorrect setting of any parameter, in other words, that VEPS is true, is a striking result. It is so striking not only because the evidence is so strong and so without exception, but also because the result itself is so surprising. When the Principles and Parameters theory was first created, the natural expectation in both linguistic theory and in the field of language acquisition was that children would sometimes mis-set parameters, and that this mis-setting would be the cause of children's 'funny' language productions. Thus Hyams' (1986) result which seemed to show that children in English mis-set the null-subject parameter was quite important, because it was the first discovered case which seemed to actually show in empirical language acquisition studies that parameters were mis-set, something which had been thought to be a natural result. Of course we now know, as demonstrated in this section, that the null-subject parameter is not mis-set. Why was it expected by the field as a whole that parameters would be mis-set? The reason, I believe, was the (sometimes implicit, sometimes explicit) assumption of LLEE (Section 0): Late Learning Early Emergence. In the Principles and Parameters theory, Principles were in general assumed to be innately specified in the genetic program; this was what is called Universal Grammar (UG). Parameters, on the other hand, represented what had to be 'learned' from experience. Given the assumption of LLEE, it was thus predicted that while principles should be known to the young child, parameter values would be set correctly at a later age, since learning was 'late'. Thus the demonstration that VEPS is true must be taken as strong evidence against LLEE. This is an important foundational result for the field, because it means that the fundamental intuition of the field of first language acquisition that non-adult grammatical productions in children were the result of faulty learning cannot be easily maintained. Given the failure of faulty (i.e. late) learning as an explanation, it follows that a different explanation of children's non-adult grammatical productions is clearly not V2 in embedded clauses. The statistical result is extremely strong, and the effect of the children's productions quite odd to a native speaker. Moreover, Schoenenberger (1998) has provided experimental evidence which confirms the evidence based on natural production data for a larger group of children. However, Schoenenberger (1998) argues on the basis of convincing distributional evidence that the children have not mis-set the embedded V2 parameter (or its equivalent in any syntactic theory of Swiss-German). Rather, she argues, the children have mis-classified some complementizers (C, heads) as full DP's, and thus place them in Spec,C rather than in C. Given the grammar of V2 languages, since Spec,C is filled (by the mis-analyzed Complementizers), movement of C is necessary, so that C is not empty. Thus the finite verb moves to C. On Schoenenberger's analysis, the parameter is a unitary V2 parameter whose effects in embedded clauses differ from matrix clauses in the adult language only because C is filled in embedded clauses. Thus children have set the V2 parameter correctly. Two important questions remain. One, why do the children mis-classify the complementizers as DP's? (Schoenenberger provides some speculation on this question.) Second, what is the relation between a mis-classified complementizer and the mis-setting of a parameter? What leads to the mis-classification of a lexical item? Is this dangerously close to the mis-setting of a parameter for VEPS' comfort? It seems to me that these are important questions for further investigation. It would also be interesting to discover any further cases of systematic mis-classification of items which such grammatical content.
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must be discovered, because children's early productions are quite often non-adult in certain ways. The natural assumption, of course, when learning fails, is that certain properties of grammar grow or mature, in the sense of Borer and Wexler (1987, 1992). For a current discussion of maturation see Wexler (in press). This is not the place to discuss the conceptual and foundational issues in any detail, but I will simply point out that Wexler argues in that paper that the only known alternative to maturation and learning - that 'performance' factors are the only or major cause of children's non-adult grammatical productions - cannot work as an explanation (see also Grain and Wexler (in press)). Thus we are left with maturation as the only viable explanation for a substantial number of properties of children's language which vary over time. Of course, such an explanation is the most natural one, given the assumption that grammar is instantiated in the human brain as a biological entity. Growth or maturation or development is perhaps the key feature of human biology. Thus the empirically-discovered need for maturation (given all the evidence produced on other topics, plus the new evidence from VEPS (that LLEE is false)) is actually a welcome result, since it shows that the most general biological model indeed is extendible to human language. Moreover, the assumption that language 'grows' in the mind/brain is the basic assumption of linguistic theory, so that the concept of language growth/maturation reintegrates the study of language acquisition with the study of linguistic theory. For further extensive discussion, comparing maturation with its opposite - 'rigidity' - see Wexler (in press).
7. Very early knowledge of inflection As mentioned earlier, VEKI is very close to VEPS, since inflectional material and parameters are closely linked theoretically. Thus the evidence that we have discussed which supports VEPS also supports VEKI. But, more specifically, we can ask whether the grammatical and phonological properties of specific inflections are known, in addition to the properties which induce what have been called syntactic parameters such as V-raising. One important set of inflectional items is the set of agreement morphemes. Are these known to young children? With respect to verbal inflection, Wexler (1990, 1994) argued that much of it is known to very young children. For example, Poeppel and Wexler argued that young German-speaking children (in their case a child of 2; 1, but they also discussed evidence from the data of Clahsen, 1991) do not make agreement mistakes; if they produce a verbal inflection, then the subject appropriately agrees with it. For example, if the child produced third person singular t on a verb, then the subject was third person singular more than 95% of the time. Likewise, if a subject has certain phi features, then an inflection on the verb will not have contradictory phi features. To take a well-documented example, the following table from Harris and Wexler (1996a,b) shows the frequency of English verb inflections with all first singular nominative pronoun subjects in a number of CHILDES corpora, over a number of children. See Harris and Wexler for the exact corpora.
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(15) stem 1349
irreg pst 325
ed 47
s 3
The number of third singulars on verbs with I as subject is vanishingly rare, only 3 out of more than 1,700 sentences which have / as a subject. Children simply don't say / likes ice cream. Harris and Wexler (1996) also show that s occurs much more frequently when the subject is third singular - she likes ice cream. (It shouldn't always occur; the lack of s indicates an OI, as Wexler (1990ff.) argues.) The conclusion is that the correct agreement features on verbal inflectional morphemes are known. Moreover the general phonological properties of the agreement morphemes are known. Thus children know that the phoneme /s/ in English is specified as +3rd +singular +present. Similarly for German t as argued above, etc. Of course, there may be some morphemes whose inflectional properties are not known at the earliest stages, since these must be learned. But in general, the morphemes of verbal agreement do seem to be known, in the sense that their phonology is in general known and their grammatical features are known. Some basic morphemes of tense are also known. Until recently it hadn't really been established, so far as I know, whether children knew the grammatical (tense) properties of the third singular present morpheme s or the past morpheme ed in English. This is because it isn't always easy to tell in natural production data what tense is intended by the children. However, there is now excellent evidence that young children know the grammatical properties of these morphemes. Rice et al. (1995) and Rice and Wexler (1996) did an elicitation experiment for present s and past ed morphemes, establishing the time context quite clearly. There were 40 children with mean age 3;0 in the Rice and Wexler study. The basic outline of the results is as follows. When a present context was used, children either used the correct inflectional present verbal form she paints pictures or an OI she paint pictures. When a past context was used, children either used the correct past verbal form she painted pictures or an OI she paint pictures. Out of large numbers of elicited productions children almost never used a present form s in a past context or a past form ed in a present context. There can be no question that these children knew that ed is +past and that s is -past.17 The Lexical Learning Hypothesis (Wexler and Chien, 1985; see also Borer, 1984; Manzini and Wexler, 1987 for related ideas) suggests that lexical items (including inflectional material, as emphasized by Borer) that underlie parameters have to be learned, but the hypothesis does not say when this material is learned. VEKI suggests that it general the inflectional material is learned quite early, though there is no reason to think that all inflectional material is known by the time that children are producing language (1;0 on average). In fact, Schiitze and Wexler (1996a,b) and Wexler et al. (in press) allow for the possibility and provide evidence that some case forms may not be known at a particular age, even relatively common forms. However, it is quite striking how much is known about abstract properties of verbal inflections (and of other types of inflection, such as NP inflections, including determiners, see e.g. Bohnacker (1997). In unpublished work Carson Schiitze and I have extended this result to children in their 2's.
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Again a general view in the field of language acquisition was that children have a great deal of trouble learning inflection. This view really was widely held - see, for example, Gleitman and Wanner (1982). I believe, in fact, that the belief in late learning of inflectional material was a parallel belief to late learning of parameters - both attempting to explain why children's utterances were so often non-adult like, even though they might know grammatical principles. The view was natural enough, again, given LLEE. Since the phonological and grammatical properties of particular inflections had to be learned, LLEE suggested that they would be learned late. In contrast, my view, that I think has been substantiated by now with a great deal of evidence in the Optional Infinitive stage, is that young children are extremely good at learning inflection; it is very difficult to find examples of central inflectional material that is difficult for young children to learn. In fact, I would say than an informal way to characterize some of very young children's abilities is that they are little inflection machines. Of course, it wouldn't be surprising if this is an over-statement - so many inflections remain to be investigated, and there could be all sorts of reasons that really do make certain inflections difficult to master. But I would like to propose this metaphor to counter the prevailing view that very young children are not good at inflections. 8. The AGR/TNS Omission Model As background for the continuing discussion on variation and maturation, we need to have a model of the OI stage - what syntactic properties do children in this stage show? Basically I assume that children in the OI stage have set the relevant parameters correctly (VEPS) and that, moreover, they know the relevant properties of UG. However, there is one UG difference between these children and adults. What is that difference? In Wexler (1990ff.) I assumed that children in the OI stage can optionally omit TNS from their syntactic representations. However, Schiitze and Wexler (1996a,b) argued that children in the OI stage can omit AGReement or TNS (or both, although I won't discuss that case here). I think there is good evidence for this AGR/TNS Omission MODEL (ATOM), and will assume it here. Here I will just briefly mention the evidence that Schiitze and Wexler (1996) used to argue for ATOM. Basically the evidence involved errors of subject case. Englishspeaking children often use non-NOM case in subject position (her going). Why? If TNS is omitted from the representation we can assume that a 'default' case (ACC in English) is assigned. This view predicts that ACC subjects will occur with OI's, since OI's are missing TNS. Such a view is confirmed by much data in English development. For example, here is the data from Nina, as reported in Schiitze and Wexler (1996a,b).18 18
Schiitze and Wexler provide file by file analyses showing the effect holds at different stages of a child's development; thus the effect cannot be due to both NOM and finiteness developing simultaneously. In other words, they do statistical analysis to show that there is a causal contingency between finiteness and NOM.
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(16) Nina's 3rd singular subject pronouns: finiteness vs. case (Schiitze and Wexler, 1996a,b) Subject Finite Nonfinite he + she 255 139 him + her 14 120 Percent non-NOM 5% 46% In (16) it can be seen that with nonfinite (OI) matrix verbs, 46% of Nina's pronominal subjects are ACC rather than NOM. We would expect these if default ACC were used with non-NOM subjects. Furthermore, with finite verbs, only 5% of the subjects are non-NOM. However, as Schiitze and Wexler point out, this analysis (of default ACC used when TNS is omitted) is not sufficient. The reason is that for nonfinite (OI) verbs, for which presumably TNS has been omitted, 54% of the subjects are NOM. That is, although finite verbs show almost 100% use of NOM subjects, nonfinite verbs show an alternation between NOM and non-NOM subjects. What licenses the NOM subject of OI verbs? 19 Schiitze and Wexler argue that AGR assigns NOM and that AGR may be present even when TNS is missing, resulting in an OI, but NOM case. Furthermore, Tense may be missing even when AGR is present; missing TNS results in a possibly PRO subject, thus empty subjects for the non-finite verbs, as discussed in Section 5. (17) AGRATNS Omission Model (ATOM) of OI Stage (Schiitze and Wexler, 1996a,b): a. AGR or TNS (or both) may be deleted b. AGR assigns NOM, if no AGR, subject gets default case c. Default case in English is ACC, in German/Dutch it is NOM d. Lack of TNS licenses PRO d. Morphology inserted according to Elsewhere Principle, e.g. Distributed Morphology e. Kid knows adult Syntax and Morphology (features, Elsewhere Principle, default forms) (18) Features of English Verbal Inflections (Schiitze and Wexler, 1996a,b) I si [+3rd, -i-singular, +present] led! [+past] 101 [ ] (i.e. no features, the empty inflection is default) In English, the morphosyntactic features for the verbal inflections of agreement and finiteness are specified in (18).20 Since (17e) assumes that the children know the 19 Schiitze and Wexler refine the predictions, arguing that past tense and modal verbs in English, which don't show agreement, should allow ACC subjects, and they present evidence in favor of this view. See also Wexler et al. (in press) for further evidence. 20 Notice that the model uses the Halle and Marantz (1993) assumption that in English the AGR and TNS nodes have fused, but this assumption isn't necessary for the analysis.
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relevant inflections (in accordance with VEKI), (18) is known to the child in the OI stage. The principles of Distributed Morphology (DM) (including the Elsewhere Principle) say that, at a node, various morphemes 'compete', but that the maximallyspecified morpheme which doesn't include a feature which is not present on the node will be inserted. In other words, the morpheme which has the most features in the lexicon will be inserted, so long as this morpheme does not contain a feature which does not exist on the node. It is possible, of course, that a morpheme may not specify a feature which is present on the node. Consider third singular present. If both AGR and TNS are included in the representation, then these three features will be specified, and DM predicts that I si will be inserted since it is the maximally specified consistent morpheme. Suppose, however, that AGR is missing from the representation although TNS is present, so that only +present is in the syntactic representation. I si is now inconsistent with the representation, since it is specified +3rd -(-singular, which are not in the representation, led I is also not consistent, since +past is not in the representation. However, the phonetically empty morpheme 101, which has no features is consistent with the representation, since it has no features which are not in the representation. Since no other morpheme is consistent with the representation, 101 is the maximally specified morpheme that is consistent with the representation, and it will be inserted. Thus with [-AGR, +TNS] in this (third person singular present) case, 101 will be inserted and we will get the verb like instead of the correct form likes. This is example of an OI in English. Note that ATOM predicts that there will be two kinds of OI's in English.21 Either AGR will be present and TNS missing or TNS will be present and AGR missing. Either situation will result in an OI where third singular s should appear. An OI form like Mary like ice cream will have two possible analyses. Now, suppose a third person masculine pronoun is used with this representation. Will he or him emerge? Since (17b) claims that if AGR is not in the representation, the default case is used, and since (17c) assumes that ACC is the default case in English, the ACC form (him) will emerge, and we will get (19). (19) a. him like [-AGR, +TNS] ice cream b. he like [+AGR, -TNS] ice cream Carrying through the analyses, one can see the general pattern for a child in the OI stage: (20) a. b. c. d.
21
he likes ice cream [+AGR, +TNS] he like ice cream [[+AGR, -TNS] him like ice cream [-AGR, +TNS] *him likes ice cream
Again, ignoring the possibility of both AGR and TNS being missing; see Schiitze and Wexler, 1996a; Schiitze, 1997, for discussion.
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(20d) is ungrammatical for the OI child because the presence of I si on the verb shows that AGR is present in the syntactic representation, but the presence of him shows that AGR is not present. This is the pattern of results that hold, as Schiitze and Wexler argue. (17c) assumes that 'default case' is different in different languages. Schiitze and Wexler (and for detailed argumentation see Schiitze, 1997) provide evidence for this choice in the adult language, and it is assumed (17e above) that children in the OI stage know which forms are defaults. Schiitze and Wexler use this assumption to predict the empirically correct fact that in languages like German and Dutch, the subject of OI's are almost uniformly NOM even for OI's, distinctly different from the results in English and French. I have simplified somewhat for ease of exposition. Schiitze and Wexler do not assume that there is a 'default' case in a language. Rather, they provide a set of features for the items which bear case which predicts how the less-specified forms will show up when specifications are missing. This is in accordance with the assumptions of Distributed Morphology. In particular, in English an ACC form like him will not be specified for a Case feature but will be specified only for phi features (person, gender, number). For example, /he/ is specified as [+NOM, +3rd, +singular, -i-masculine] whereas /him/ is specified as [+3rd, +singular, +masculine]. Thus when no case feature exists on a DP in the syntactic representation, only the ACC form him can be inserted, since other forms will have case features specified which will clash with the lack of a case feature on the DP in the syntactic representation. In German it is the 'NOM' form of the pronoun that has no case feature specified, whereas the ACC form is specified [+ACC]. Thus the NOM form is inserted when no case feature exists in the syntactic tree. This is a precise DM account of 'default' forms. Thus we have a case of variation in development (many subject case errors in English, none in German or Dutch), a strong cross-linguistic difference, which is predicted by a model which assumes that development of UG principles is the same in both languages (essentially as in adult language except that AGR/TNS may be deleted), and that VEPS and VEKI is true, so that the children have learned the correct values (for example, the features of verbal inflections, the features on case (e.g. NOM/ACC features are known, 'default case' is known, etc.). The 'difference' in development is simply the consequence of universal principles developing in a certain way, but interacting with (correctly) learned parameter-settings so that certain differences in surface behavior emerge. Results of this nature demonstrate in the field of language acquisition the familiar everyday lessons from science (e.g. the hard sciences) and from linguistic theory. Namely, deeper, more correct explanations of phenomena are necessary and useful; a surface difference may result from what is essentially a deeper commonality. The UG state of children in Dutch and English is the same (i.e. basically UG, but AGR/TNS Omission, in both languages). The variation (subject case 'errors' in English but not in Dutch) is due to a property of the languages themselves (the form of default case), which the children have learned, correctly, for each language. Neither language is more 'difficult' to learn; the English-speaking children simply give what appears to be a more 'incorrect' behavior (ACC instead of NOM case on subjects)
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because of the surface form of default case. The sophistication of knowledge of grammar in the English- and Dutch-speaking children is identical: UG modified by AGR/TNS Omission, together with the correct setting for default case in the input language. Why isn't omission of AGR or TNS from a syntactic representation of a root/matrix declarative sentence a violation of VEPS or VEKI? It isn't a violation of VEPS because the omission does not reflect a mis-set parameter. I am assuming that the requirement for AGR and TNS in the representation of a root declarative clause is a property of UG, whether of the computational component itself or of the interface of the computational component and the conceptual/interpretive component. There is nothing in UG that allows a 'setting' which will permit AGR/TNS to not exist in root structures. A violation of a universal, non-parametric property is, by definition, not a mis-set parameter. As for VEKI, the hypothesis that children know the grammatical properties of inflectional morphemes, note that the requirement is that children know what syntactic, morphological and phonological features are specified on a morpheme. These specifications do not require that the morphemes always appear in a sentence, even a root/matrix declarative sentence. Such a requirement could only come from a requirement that a node or phrase of a particular kind (e.g. AGR, TNS) appear in a phrase-marker (with a certain interpretation). Knowledge of inflection cannot produce the obligatory behavior. I have shown that children know the properties with which a morpheme is specified in the lexicon (e.g. that a particular agreement morpheme has certain specified agreement features, or that a particular INFL morpheme has a 'strong' property, so that movement to it must be overt). The obligatory nature of the presence of a morpheme in a structure depends on the syntactic representation, not on the lexical specification of the morpheme. Thus the omission of AGR or TNS does not violate VEKI. 9. What causes subjects of OI's to raise: D-features and the EPP A classic problem in the theory of OI's, ever since Wexler's (1990, 1992, 1994) proposal that OI's were missing INFL, is: what causes the subject of an OI to raise from a lower VP position to a higher position, the Specifier of some INFL projection. If INFL is missing, what feature is being checked when the subject raises? On Wexler's TNS-omission theory for example, if TNS is missing in an OI, why do subjects raise? An equivalent way of putting the question is: how do subjects of OI's get their case? If TNS is missing and TNS is responsible for NOM-assignment, how is NOM assigned? If default (ACC in English) case is assigned, because TNS is missing, why does the subject raise, since classically in contemporary grammar, subjects raise to satisfy a (NOM) case-feature. That is, subjects raise to INFL to get case, but if case of an OI is not assigned by an INFL element, but is default, why does raising of the subject take place? On Economy grounds, why doesn't the subject stay in place?
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The word order facts in the OI stage show that there must be a functional projection to which the subject moves. In sentences with negation, the basic word order observed is: (21) NPjNEG [ VPti V[-finite] ...] Assuming, as is standard, that NEG is generated to the left of VP and that the subject is generated in the Specifier of VP (as in (21)) or in a left-adjoined position to VP, we can see that the subject NP; raises to some position to the left of NEG. In adult syntax, this is the specifier of some INFL position. But if V is non-finite (an OI, as in (21)) then it is standardly assumed that no case is assigned to the subject of a non-finite verb, and thus case can't be assigned to NPi? the subject. The problem then is, why does the subject raise? First, let me very briefly just list some of the references which show that the subject of an OI in fact does appear to the left of negation, as in (21). (22) Some evidence for raised subjects of OI's: a. Medial Neg in English (Harris and Wexler, 1996) e.g. Mary not go b. Mainland Scandinavian OI's (Wexler, 1990ff.) though subject could be in Spec,C c. Faroese subjects before NEG in OI's, in (Jonas, 1995a,b, who shows that specific subjects exist before NEG and argues that that's a raised position in Faroese) d. French (Pierce, 1989, 1992; Deprez and Pierce, 1994; Levow, 1995) where subjects of OI's mostly appear to the left of NEG pas Although I do not have the space to review the evidence in detail here, it is accepted in the field that subjects appear to the left of NEG, even in OI's. This is overwhelmingly true. There is a small suggestion that at a very early part of the OI stage, the subject may actually not raise, and surface to the right of NEG (Pierce, 1989, 1992; Deprez and Pierce, 1994). However, at best this is a very short-lived stage. In fact, whether this possibility exists at all is not clear; Stromswold (mss.) argues that the Deprez and Pierce and Pierce evidence doesn't support the suggestion of such a possibility at all. She points out that most of the sentences with negation in initial position don't have subjects, thus making the determination of whether the subject is still in the VP impossible. She also makes a number of other methodological points. Wexler (1990, 1994) pointed out that this VP-internal stage didn't have much evidence for it, and subsequent work has confirmed rather than thrown doubt on that view. At any rate, there is no question or controversy at all, that during the great bulk of the OI stage, subjects surface consistently to the left of NEG, so that even if there turns out to be a subject internal to VP possibility, it is extremely shortlived and doesn't characterize the OI stage. Thus the problem remains: why do subjects of OI's raise, if they don't do it to receive (or check off) case? The problem is quite serious for any theory of the OI stage which assumes that children basically have UG representations and syntax. Simple theories like
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Wexler's TNS Omission theory (1990ff.) assume that this is so; but why then do subjects of OI's raise? Consider Rizzi's (1994a,b) 'Truncation Theory'. Since on this theory, OI's must be missing the TNS projection, and also any projection higher than TNS, how does the subject get case? The assumption of this theory is that the relevant functional projections come in the order AGRP TP VP. Thus an OI is a bare VP since it is missing TNS and thus all higher projections. But how is case assigned to the subject of a bare VP? In fact, Rizzi at least speculates that all subjects of OI's are in fact in some kind of adjoined 'Topic' position, which isn't represented at all by a functional category, something like (23): (23) MSubject.tvpti...]] Presumably the subject has raised to some kind of 'Topic' position, for semantic, not case reasons. This proposal leaves at least two questions unanswered. First, how does NOM case get assigned to the subject if there is no appropriate inflectional projection to assign it? (We know, even from the English facts, that NOM is often assigned, even though it is not default). Second, why should all subjects of OI's be in topic position? There is no evidence to support this view. Basically, Truncation theory has a difficult time with the raising and case of a subject.22 Schutze and Wexler's (1996 a,b) AGR/TNS Omission Model described in the last section predicts that when NOM is assigned by INFL, AGR is in the representation, so that if the sentence is an OI, TNS must be missing. So far, so good, AGR (which assigns NOM) motivates the raising of the subject, so that case can be assigned/checked. But what happens when TNS is present and AGR is missing, as ATOM assumes is possible? Default case is assigned under straight-forward assumptions from Distributed Morphology. That is, if no case feature is specified on the subject (since AGR is not present), then only the ACC form of the pronoun (which has no case features specified on it in English) will be consistent with the representation, and this ACC form will be inserted. (See an earlier footnote). So far so good. But why does the subject raise? In fact, the subject does raise even in this case, when default case is assigned, producing forms like (24a), but not (24b): (24) In the OI stage: a. him [Default case] not go (OI stage word order) b. *not him [Default case] go (NOT the OI stage word order)
22
A related problem for Truncation theory is that it predicts that OI's are not possible with negation, since NEG is superior to TNS, and thus NEG is omitted whenever TNS is omitted. Rizzi takes this as a virtue of Truncation Theory, since he argues that the facts are true for French. But, in fact, as Levow (1995) has shown, there are ample number of negative OI's in the French OI stage. Of course, negative OI's are also abundant in the Germanic OI stage, a fact which caused Haegemann (1995) to propose that NEG was below TNS in Germanic, thus allowing NEG w/out TNS under Truncation. The facts of negation in the OI stage thus argue against Truncation, unless negation were universally under TNS, which would cause other problems for the Truncation model.
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Moreover, in the other Germanic languages, since sometimes the observed NOM is default (when AGR is missing), we would expect some NOM subjects in those languages to appear to the right of negation, but they don't. Thus it is quite clear that all subjects, whether assigned NOM or not by INFL (AGR) raise out of the VP. The AGR/TNS Omission Model at least allows a functional position for the subject to move to in an OI (AGR or TNS, when the other one is missing).23 But it still leaves unanswered the question of why the default-case subject of an OI raises up. If TNS doesn't assign case, and AGR is missing, by Economy (Greed) we should expect the subject to not raise. Under any theory that assumes that subjects raise to be assigned case, we would expect that the subject of an OI with the case-assigning projection AGR missing would not raise, and would stay to the right of negation. This problem of the raising and case assignment to the subject of an OI has been a serious and interesting problem in the theory of OI's. If it couldn't be solved, we would be left with a real dilemma about the nature of the child's knowledge of UG. It is a virtue of the precise investigation of children's grammar in the OI stage that the problem has indeed surfaced. In my opinion, it is a sign of the maturity of the field of developmental psycholinguistics that a problem of this nature could even arise. For it takes enough structure to the theoretical analysis to let a problem arise. It is thus gratifying that in fact a rather satisfying answer has emerged. Chomsky (1995: Chapter 4) argues that it can't be a Case property that attracts the subject out of VP to a Spec, INFL. Subjects raise to higher positions even when they don't receive Case there. So EPP (the Extended Projection Principle) is not driven by Case in a Minimalist (Economy) theory. Consider an infinitival (raising) construction, as in (25): (25) Mary INFL(+FIN) seems [e, to INFL(-FIN) [VP e2 like it here] DP Mary in (25) first moves to the lower Spec, INFL, but it doesn't receive Case there, since non-finite INFL doesn't assign (or check) case, certainly not NOM case. In general EPP applies cyclically, and can apply many times, but Case is only checked once, when NOM is assigned/checked. But if case is the reason for movement of the subject, there would be no reason for the subject to undergo its first move, the subject of the non-finite INFL. Economy (Greed) would thus predict that it wouldn 't move. However, it does move. Thus case checking cannot be the reason for the movement of the subject, for EPP. Thus Chomsky proposes (26). (26) EPP is the requirement that a D (Determiner) feature be checked
23
Schutze and Wexler (1996a,b) and Schutze (1997) discuss the possibility that when both AGR and TNS are missing, GENitive case surfaces on the subject - my go. If both AGR and TNS are missing, how could the subject raise? Where is it sitting? In fact, we don't know whether genitive subjects do raise to the left of negation. There isn't enough analyzed empirical material at the moment to discuss this situation, so far as I know. See Vainikka (1993/94) for a discussion of genitive subjects in young English-speaking children.
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In other words, the INFL projection has a D-feature which must be checked by a suitable D-feature on a DP. The subject raises up and checks off this feature. Crucially, the relevant feature is not a Case feature. Thus in infinitivals such as (25), the non-finite lower INFL has a D-feature which must be checked. Thus it attracts the subject DP Maty, which has this D-feature. The upper (finite) INFL also has a Dfeature, which must be checked, so it then attracts the DP Mary, checking off its Dfeature. In OI representations, the INFL is non-finite. But it still will have a D-feature, just as infinitives do in the adult grammar. Thus this D-feature will still have to be checked off, and the subject to raise to Spec,INFL to accomplish this, even when no case-assignment or checking is accomplished by INFL (again as in some embedded infinitival constructions in the adult grammar, as in (25)). Thus the problem of why subjects raise in OI representations is solved; in fact, raising is forced, by the same mechanisms which force raising in the adult grammar. Case assignment or checking is seen to be irrelevant, whether in adult representations or in OI representations. To see this in more detail in the ATOM, we assume (27). (27) Both AGRS and TNS have a D feature24 which must be eliminated by checking against the D-feature of a DP which raises up for checking Briefly and informally, what forces movement in the (Chomsky, 1995: Chapter 4) theory that I am adopting is that -Interpretable (non-interpretable) features (that is, features that play no role at LF) must be eliminated by checking, thus they delete as soon as they check and they obligatorially check, so that they can delete. Chomsky (1995: 282) assumes that "features of the target that enter into checking relations [are] invariably -Interpretable". Otherwise the movement/checking would be "locally superfluous", so that the -Interpretable nature of the target features helps to avoid "excessive computational complexity" (1995: 283). The functional categories are the targets, thus it is their features that are necessarily -Interpretable. Thus Dfeatures on AGRS and TNS must be -Interpretable (in contrast to the D-features on a DP, which are interpretable and thus don't delete after checking). Chomsky (1995: Chapter 4) assumes that TNS has a D-feature. When this feature is strong, overt movement is forced, thereby displaying the Extended Projection Principle effects. I am assuming in (27) that AGRS also has a D-feature, so that 24
I have worked out the theory here assuming that AGRS heads a projection, just as does TNS. Chomsky (1995: Chapter 4) questions the assumption that AGR heads a projection, and the issue remains open (see Jonas (1995a,b) for arguments that an INFL projection in addition to TNS is necessary). If it turns out that AGR should not be looked on as heading a projection, then it seems possible that a theory in the same spirit as I present here can be implemented. Possibly a single INFL projection will have both TNS and AGR features, either of which may be omitted by the OI child. One might attempt to replicate the effect of AGRS in the OI stage with considerations of the verbal functional category v of Chomsky (1995: Chapter 4). However, there doesn't seem to be an obvious way to then explain the relation between null-subject languages and the lack of the OI stage, as is done with AGRS in Section 12. See Schiitze (1997) for additional discussion.
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movement is forced to AGRS as well as to TNS, checking the D-feature in each case. I am making no particular assumptions about whether the D feature on AGRS or TNS is strong in every language; it could vary across languages and possibly vary between AGRS and TNS even in a language. Based on the child data in the OI stage we will return to this question. In finite clauses (adult or child), the D-feature on TNS attracts the subject to raise to Spec,TNS and then the D-feature on AGR attracts the subject to raise to Spec,AGR. In OI's, according to the ATOM, there are two possibilities, with AGR present and TNS missing, or with TNS present and AGR missing.25 (28) a. NPj [No CASE Assigned] TNS[D] [ VP ti V...] b. NPj [NOM] AGR[D] [VP t; V...] (29) a. him like ice cream b. he like ice cream If TNS is present, but AGR missing, as in (28a), the D-feature on TNS causes the subject to raise. Since TNS by itself does not assign case, no case feature is assigned/checked by TNS and Default case is spelled out by the morphology, yielding (29a). If AGR is present, but TNS is missing, as in (28b), the D-feature on AGR causes the subject to raise. Since AGR assigns/checks NOMinative case, this shows up on the subject, yielding (29b). Note that the subject raises up in OI structures in English whether or not NOM has been assigned to the subject, as we have pointed out. Thus the subject raises up whether AGR or TNS is the sole INFL category in that structure. Thus we can conclude from the child grammar that AGRS and TNS in these languages both have a strong D-feature. Whether the D-feature on AGRS and TNS must have the same strength value for a given language remains to be investigated. Consider VSO languages, like Irish. Carnie (1995) argues that the subject actually raises up to the lower of two INFL positions, but that the verb raises up to the higher of the two INFL positions, the VSO order resulting. We can take the higher position to be AGRS and the lower position to be TNS. Thus the subject raises up (overtly) only to Spec, TNS. Thus in Irish we can take the D-feature on TNS to be strong but the D-feature on AGRS to be weak. Thus, apparently, the strength of the D-feature on AGRS and TNS can vary within a language. Consider the OI stage of Irish, as mentioned by Wexler (1995). Suppose both AGRS and TNS are present, then we get the adult VSO finite structure. Suppose AGRS is missing from the structure but that TNS is present. Then we get a nonfinite verb (because agreement can't be checked). The non-finite verb doesn't raise and the subject raises up overtly (via the strong D-feature on TNS) to Spec,TNS. Thus we get a non-finite SVO structure (and since AGRS isn't present, the case on 25
Again, for simplicity we ignore the possibility of both AGR and TNS missing. See an earlier footnote for discussion.
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the subject is whatever Irish default case turns out to be). Suppose, on the other hand that TNS is missing from the structure, but AGRS is present. Again, we get a nonfinite verb which doesn't raise, and a subject in this case which doesn't raise overtly, again yielding an SVO non-finite structure. In this case, NOM case will be assigned to the subject since AGRS is present (and the checking can take place at LF). As Wexler pointed out, the pattern is VSO finite sentences and SVO non-finite sentences is exactly what is observed in child Irish. (I know of no reported evidence on subject case in OI Irish.) The UG-motivated assumption (26) that subject-raising (EPP) is motivated by a categorial feature rather than a case feature solves the problem of why the subject moves up even though it doesn't receive structural case in OI's. Motivation of movement through a categorial feature thus receives strong support in acquisition research concerning very early inflectional development. As has happened before (e.g. the case of Binding Principle B, and the distinction between binding and reference; see Wexler and Chien, 1985; Chien and Wexler, 1990; Avrutin and Wexler, 1992; Wexler, in press), the child's grammar shows a grammatical process in a purer form than does the adult grammar. Adults must have AGR in root clauses, and thus NOM case is assigned, and it appeared as if it was Case that was driving movement. The child, in the same simple clause, can be missing AGR, so that it becomes quite clear that Case can't be driving movement; the actual underlying process shows up more clearly than in adult grammar, where it was obscured by the obligatory existence of AGR (and thus of NOM case on the subject) in standard declarative clauses.26 One might ask, how can a representation which is missing AGR (or TNS for that matter) still allow us to claim that basically children are applying UG syntax, since these projections are obligatory in simple clauses. It is quite difficult to find a principle of syntax which requires the existence of AGR or TNS in a clause. If one searches through, say, GB syntax or Minimalist syntax, one doesn't find a principle which requires the presence of these projections. Rather, the projections are assumed to exist, and then, given properties of syntax, certain consequences follow, for example, the raising of a subject. Even the existence of TNS is not explained in the syntactic theory. Perhaps the best place to look for conditions which would make TNS obligatory in declarative root clauses would be a theory of the syntax/interpretation interface, for example, in some kind of 'Anchoring' Principle (En£, 1987). But it is important to stress that the existence of these projections in declarative representations is not part of the 'Computational System' of the syntax, as discussed in Chomsky (1995). Thus to the extent that the child is omitting projections, it might be looked on as an 'interface' property that the child is making a mistake on. Wexler (in press) formulates the hypothesis that much (most? all?) of syntactic development 26 Of course there are some non-finite root clauses in adult grammar, for example various kinds of exhortatives (Rain in Edinburgh? Never!), but these are marginal enough that they haven't played much of a role in the discussion of the syntax of basic clause structure. For discussion of the relation of nonfinite root clauses in adults to non-finite root clauses in children, see Weverink, 1989; Wexler, 1990ff.; Rizzi, 1994a,b among others.
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(growth) (as opposed to 'learning', as in parameter-setting) is the growth of interface properties, perhaps in a way analogous to the growth of coordination of other physiological systems (e.g. eye-hand coordination). However these more broad issues turn out, the fact that there was a word order problem (why does the subject of an OI raise?) and a case problem (how is it possible that the subject of an OI can receive NOM CASE or non-NOM CASE, when it's clear that children know case syntax and morphology) should have driven acquisition researchers to create a theory of syntax which does not assume that case is what drives the EPP (raising of a subject). The data is actually better in Acquisition, in my opinion, because of the existence of OI's, than in adult syntax. Even though the syntactic theory of D-motivation of EPP was developed independently of the acquisition results, I hope that this discussion of why the acquisition results should have led acquisition researchers to reformulate the theory of UG will have the effect of making researchers more open to using theoretically and empirically well-grounded acquisition results as the basis for reformulating elements of the theory of syntax in the future. Of course, the basic assumption that is necessary for such an approach is that the computational system of the syntax is mostly in place in young children, an assumption which seems to me by now to be well-grounded empirically. I hope here to have demonstrated that the OI child is a model system for teasing apart the affects and syntactic significance of specific INFL categories. Studying an OI child is like studying an animal with a gene 'knock-out' technique. The fact that the OI child is missing highly specific aspects of grammar (perhaps interface aspects) allows us to deduce which properties of UG are determined by these aspects. In my view, the case for the integration of child syntax and adult syntax is now substantial, not only in principle but in practice. Moreover, the influences of the fields can and should (in practice as well as in principle) be bi-directional. As Hamburger and Wexler (1973) concluded in their last sentence, "[t]he bridge that Chomsky has re-erected between psychology and linguistics bears two-way traffic". 10. Developmental variation across languages. The null-subject/optional infinitive correlation Before we turn to the important question of what causes the OI stage, we should note that there is variation across languages; some languages appear not to undergo an OI stage, as suggested in the original cross-linguistic description (Wexler, 1992, 1994). If some languages don't go through the OI stage, how can we say that the stage is the result of universal linguistic growth or maturation? Doesn't the very existence of the cross-linguistic variation imply that the finiteness requirement is easier to 'learn' in one language than in another language, so that the OI stage itself must be the result of some kind of slow or difficult learning? The answer is 'no'; as we will see in the next section, the cross-linguistic variation is once again to be considered as the consequence of a universal (across languages) development interacting with particular well-learned properties of a language. First, however, it is neces-
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sary to find the correct empirical generalization concerning which language undergo the OI stage. This is not the place to review the evidence concerning particular OI languages in any detail, but let me just extremely briefly summarize the general outline. What do I mean by an 'OI language'? Namely, one in which in early development a substantial proportion of root clauses (that in the adult grammar are required to be finite) are produced by the child in non-finite form. There is sometimes confusion about the name Optional 'Infinitive'. Even in the earliest work (Wexler, 1990,1994) it was understood that OI's are not only what is usually described as 'infinitives', but that there are a variety of non-finite forms that appear in the stage (e.g. missing auxiliaries mean that finiteness isn't marked, as in Mary going (a common sentence in the OI stage instead of Mary is going in English). The usual measure, however, is the proportion of clauses that should be finite that are actually produced as infinitives,27 and that is the measure that I will adopt here (In fact we will see later that a language may, on principled and empirical grounds, not literally have root infinitives, but may have other types of non-finite forms.) Again, for reasons of space I won't actually discuss the percentage of OI's in each language, but simply list them according to what is generally understood about them, basically following Wexler (1990ff., 1996), though with some additions.28 (30) OI languages: All Germanic languages studied to date, including Danish, Dutch, English, Faroese, (Jonas, 1995a,b); Icelandic (Sigurjonsdottir, 1992); Norwegian (Wexler, 1990, 1994); Swedish (Wexler, 1990, 1994). Also French (Pierce, 1989; Weissenborn, 1991). Also Irish (Wexler, 1995, based on data in Hickey, 1990; see also Guilfoyle, 1996); Russian (Bar-Shalom and Snyder, 1997); Brazilian Portuguese (Wexler and Secco, in preparation); Czech (Moucka and Wexler, in preparation). (31) Non-OI languages: Italian (Wexler, 1992, 1994, based on Schaeffer, 1990 data; Guasti, 1994); Spanish (Grinstead, 1994; Torrens, 1995); Catalan (Torrens, 1995); Tamil (Sarma, 1995); Polish (Klepper, 1996). Based on (some of) the above observations, Wexler (1990, 1994) suggested it was rich agreement languages which didn't allow OI's, but some of the non-OI languages (e.g. Icelandic) have almost as rich agreement as Italian, perhaps as rich, depending on verb conjugation. Also, surface morphology usually doesn't turn out to be exactly identical with underlying grammatical process in syntactic investigations,29 so it would be surprising if the existence of such a striking and consistent
27 Again, it has been known since the earliest cro'ss-linguistic work on the OI stage (Wexler, 1990ff.) that the infinitival particle (to in English, zu in Gei/man, de, a in French, etc does not show up on the OI verb. Thus 'infinitive' refers to the form of the verb itself, an aspect of verbal morphology.) 28 Percentages of OI's in various languages, compared, can be found in many references, including Phillips (1995a,b). 29 For example, although there definitely is a correlation between richness of verbal morphology and licensing of null-subjects (putting aside languages like Japanese, etc.), still there is no agreed-on precise
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piece of developmental syntax as the Optional Infinitive phenomenon was strictly tied to surface morphology. As an empirical generalization based on the above material, Wexler (1996) (see also Sano and Hyams, 1994) proposed the Null-Subject/OI Generalization. (32) The Null-Subject/OI Generalization (NS/OI) Children in a language go through an OI stage if and only if the language is not an INFL-licensed null-subject language. Wexler based this proposal on the contrast between languages like Italian, which don't show OI's, and the Germanic languages and French, which do show OI's. Since then there has been a substantial amount of research on the OI stage which substantiates the conclusion. It is important to understand the nature of the proposal. Some languages omit many subjects but don't seem to license subject-omission through INFL. Rather the subjects seem to be omitted through some kind of a discourse process. Thus, although Polish and Russian both allow subjects to be omitted, Franks (1995) argues that Polish is an Italian-style (i.e. INFL-licensed) null-subject language, whereas Russian isn't. Thus we expect Russian to show OI's in an early developmental stage, but Polish to not show OI's. Such appears to be the case (BarShalom and Snyder, 1997, for the Russian data, as well as for discussion of the nullsubject status of Russian and the relation to NS/OI; Klepper, 1996, for Polish). Similarly, Czech is classified by Franks (1995) as probably/possibly null-subject, but it definitely shows properties (e.g. overt expletives and the strong possibility of unmarked subject pronouns) which lead Moucka and Wexler (in preparation) to consider it not a null-subject language, and therefore we would expect it to have OI's. A rather striking case is Hebrew, since it is well-understood (e.g. Borer, 1984) that part of the verbal inflection paradigm in Hebrew (non-present, non-3rd person) licenses null-subjects, whereas part of the paradigm does not license null-subjects, although discourse-related omitted subjects are possible. Rhee and Wexler (1995) showed that NS/OI holds within Hebrew, that is OI's are allowed only in that part of the inflectional paradigm which does not license null subjects. Thus NS/OI seems to hold, so far rather strongly. It is a striking generalization which has a good deal of empirical support, making rather subtle and precise predictions concerning separation between languages on syntactically deep characteristics. It cries out for explanation. Of course, the explanation of NS/OI requires first an explanation of why OI's occur. Before proposing such an explanation in the next section, I would like to mention again the great value of detailed empirical quantitative research in development morphological characterization of languages which license null-subjects. Similarly, although there is definitely a correlation between richness of verbal morphology and verb-raising, the search for an empirically adequate statement of this correlation across languages is only partially successful. The appropriate conclusion seems to be that the syntactically-relevant morphological property is somewhat more abstract than can be stated as a generalization over surface morphology, thus, certain languages have an INFL that licenses and identifies null-subjects, others don't. It is this kind of syntactically-relevant feature that we should look for in attempting to generalize as to what features of a language license OI's.
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related to clear ideas of syntax. Without both a detailed quantitative map of aspects of children's early verb forms in many different languages and an understanding of the syntax of these languages (so that one can distinguish between surface characteristics of morphological forms and the question of what are the more abstract syntactic characteristics of the languages) it would have been impossible to arrive at such clear and striking generalizations. In my opinion both the methodological and theoretical depth of the study of language acquisition has increased markedly in recent years, and the fact that both methodology and theory have been treated rigorously together is one of the more salient reasons for this increase in insight in the field. In my opinion, the traditional dichotomy in the field of developmental psycholinguistics between 'theory' and 'empirical methodology' was always a red herring; one can hardly separate the two in serious research. The methodological and empirical standards of the field have been raised by OI research - given the nature of science, which is always at its best an interaction between theory and experiment - it could hardly be otherwise.
11. What causes the OI stage?: The Unique Checking Constraint 11.1. The Unique Checking Constraint defined and the derivation of ATOM Wexler (1990, 1994) proposed the TNS-omission Model of the OI stage, and suggested that it was properties of the child's knowledge of TNS that resulted in the OI stage.30 Since the ATOM argues that AGR as well as TNS may be deleted in the OI stage, we cannot do empirically with a strict model of TNS-omission, but must rather explain why AGR or TNS may be deleted. Furthermore, any theory of OI's should explain why NS/OI (32) holds. Why is the AGR or TNS projection omitted in some L's early on, while not in other L's? Therefore, we must attempt to derive the (so far empirically adequate) AGR/TNS Omission Model from more fundamental assumptions and then attempt to understand why null-subject languages show different effects from non-null-subject languages. We must explain: (33) In a. b. c.
the OI stage: Finite sentences are sometimes used Non-finite sentences are sometimes used Finite and Non-finite verbs show up in the appropriate positions
30 Wexler proposed three different models, which differed in a number of ways. The details don't matter here, only the point that it was knowledge of TNS that was relevant. I should also point out that it has been suggested in other places (for example Sano and Hyams, 1994; Wexler, 1994, 1996)) that the knowledge of TNS that children didn't have was a kind of pragmatic or interpretive knowledge. This is consistent with the point I made earlier in this paper that linguistic development in general, and development out of the OI stage in particular, might be due to development at the interface. However, given the arguments of the ATOM that AGR can be omitted along with TNS, it does not appear as if the OI stage is due purely to properties of TNS.
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d. Case and finiteness properties follow the ATOM e. NS/OI holds, that is, the ATOM doesn't hold for null-subject languages OI's are not used Ever since the TNS-Omission model of the OI stage in Wexler (1990ff.), there have been a variety of models of the OI stage proposed. Although different in quite interesting detail, they all bear a strong resemblance to the TNS-Omission model. Namely, they all propose that the underlying cause/analysis of the OI stage involves the ability to omit certain functional features or projections in the syntactic representation, or to put it another way, the lack of knowledge of the obligatoriness of certain features or projections. In some sense, from the TNS-Omission model to the current model, it is the underspecification of a feature and/or projection that characterizes models of the OI stage. Thus the TNS-Omission model assumes that children have a problem with TNS so that TNS is omitted, and this characteristic holds over the three models presented in Wexler (1994). Similarly, Rizzi's (1994a) truncation theory assumes that OI children omit certain projections because of the lack of knowledge that the root of a sentence must be CP; thus certain projections are omissable. Schiitze and Wexler's AGR/TNS Omission Model modifies the TNSOmission model so that AGR may be omitted as well as TNS. Finally, Hoekstra et al. (1996) assume that the number feature may be omitted in the OI stage rather than the TNS feature. In order then, we have models of the OI stage which involve underspecification of TNS (Wexler), any (functional?) category (Rizzi), AGR and TNS (Schiitze and Wexler) and number (Hoekstra et al.). In this section I would like to propose an entirely different kind of model, which accounts for the OI stage and its properties not as the direct result of the underspecification of a feature, but from a more fundamental constraint on the computational system of syntax. I intend by this move to integrate a wider variety of developmental phenomena together and also to tie the theory of the OI stage closer to current syntactic theory. The underlying theory will involve deeper derivations than the underspecification theories proposed to date since the assumptions will be further from the data described. If correct, such a move has illuminating consequences for a science, as linguistic theory has demonstrated. It is more difficult to easily believe in such a theory, of course, because it is less directly phenomenological, depending on its support for its ability to describe and predict a wide variety of phenomena.31 Such a theory should be proposed tentatively, but vigorously pursued. In fact, the theory to be presented will integrate a wider class of phenomena, in an unpredicted way, not only deriving properties (33) above, but also applying for example to Italian structures in the OI stage that have been previously unexplained, or even discussed, given that it was thought that Italian was not an OI language. Thus the promise for such a theory has begun to be met. Future research will indicate whether such deeper theories may in fact be important to investigate in the study 31
See Wexler (1982) for a discussion of Einstein's observation that as science advances just such nonobvious, less common-sensical theories and concepts become necessary.
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of linguistic development. Experience in other areas of linguistics as well as in science more generally suggests that they will. The question to ask is, why are finite sentences sometimes not the representation used by the OI child, especially since, as Wexler (1990ff.) argues, the child knows completely correctly all the relevant finite morphology? Let us look at the structure and derivation of a finite sentence using the syntax that we have proposed, following fairly standard assumptions. (34) a. AGRS[D] TNS[D] [ V P DPV...] b. UoRspDPj AGRS0 [TOSpt, TNS0 [ypt, V...]]] As before, for illustrative purposed I am using English SVO (left-headed) word order, but the structural properties apply to right-headed languages as well; the order of constituents is irrelevant. (34a) shows the left to right order of the functional projections AGRS and TNS, followed by the VP with its subject DP. As we assumed in (27), both AGRS and TNS have a D-feature, which implies that a D-feature must raise to check them off since features of functional categories like AGRS and TNS are -Interpretable and -Interpretable features must be eliminated. Following usual theory, the subject DP first raises up to check off the D-feature of TNS and then raises up to check off the D-feature of AGRS. The derivation is shown in (34b), with traces of the subject DP in the original position of the subject in the VP and in its intermediate position, after the first movement, in Spec,TNS. The final position is Spec,AGRS. What could go wrong for a young child with this derivation of a finite sentence in (34b), given that the child knows the morphology associated with AGR and TNS and the relevant syntax? What might be problematic for the child is the fact that two checkings are required, that DP must check its D-feature twice, first against the Dfeature of TNS, then against the D-feature of AGR. (35) Unique Checking Constraint (UCC) (on kids in Ol-stage) The D-Feature of DP can only check against one functional category. Sometimes a child produces finite utterances, and UCC doesn't apply (we will later discuss why UCC only seems to apply sometimes). Consider a simple declarative sentence. Suppose UCC does not apply to a child's representation. Then the child carries out the derivation in (34), checking the D-feature of the subject twice, and producing an adult finite sentence as in (36a). (36) a. Mary likes ice cream b. Mary like ice cream Now suppose the child attempts to derive a representation for a simple declarative sentence, but assume that this time the UCC (35) does apply. The child will have a beginning representation like (34a). The D-feature on TNS will attract the D-feature of the subject DP and the D-feature on TNS will be checked off. But now AGRS
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must have its D-feature checked. However, since we have assumed that the Unique Checking Constraint (UCC) in (35) applied, this D-feature, having already checked the D-feature on TNS, can not check a second D-feature, on AGRS. Thus the terminating representation will be (37). (37) AGRS[D] [DPjTNS [ V p t j V . . . ] In (37) I have indicated by the notation [D] that the D-feature of AGRS remains unchecked. Since by (27), the D-feature of AGRS is must be eliminated by LF (since, as the feature of a functional category (target) it is -Interpretable), the representation in (37) fails to converge, and is ruled out as ungrammatical by the grammar. That is, we assume (38), the unmarked fundamental assumption on children's grammars, since it is UG-consistent, and an assumption for which there is excellent evidence given all the knowledge of early syntax that we have demonstrated, in particular the demonstration that the subject raises up to the left of negation in English and similar languages: (38) Children in the OI stage know that: a. the features of functional categories are -Interpretable b. a derivation with unchecked -Interpretable features doesn't converge (is ungrammatical) Given that we have assumed that UCC holds and have shown that the derived representation in (37) then fails to converge, and that the child knows this (38), how can the child obtain a grammatical representation? We are continuing to assume that the child in this instance is governed by UCC. Given that UCC holds there is no way for the lexically-induced representation (34a) to converge. Therefore, the child attempts the minimal meaning-preserving change to (34) that will allow convergence given UCC.32 This change will be to only allow one INFL functional category, either AGR or TNS, so that all (i.e. only one) D-features are checked, even given UCC. Thus the child uses either representation (39a) or representation (39b): (39) a. AGRS[D] [VP DP V...] b. TNS[D] [ V P DP V...] That is, either TNS is omitted (39a) or AGR is omitted (39b).33 The subject DP in either case is raised to check off the D-feature of the INFL functional category. 32
For simplicity of presentation I am talking about what the 'child attempts', etc., but I definitely do not intend that as a serial order proposal or at all as a production model or processing model of any kind. I am talking about alternatives in the grammar of the child. When I discuss implementations of UCC later in this section (for example, as Minimize Violations) this will become quite clear. The 'alternatives' are no more to be looked as a alternatives in a production model than are alternatives in any kind of grammatical theory which compares potential representations. 33 One important point which there is no room to discuss here is that it should be possible to distinguish more than one kind of OI in some languages, depending on whehter AGR or TNS is omitted. For
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Since there are no unchecked (i.e. undeleted) -Interpretable features, the derivation proceeding from (39a) or (39b) converges. But given the child's knowledge of Distributed Morphology and the morphophonological features of the language, as discussed in the presentation of ATOM in Section 8, in some cases the adult inflectional material (made necessary by the presence of both AGR and TNS) will not be spelled out; rather the inflectional material appropriate to representation (39a) or (39b) will be spelled out. In the case of English third person singular present main verbs it turns out that in either case (39a or 39b) the spellout is the same - as the zero morpheme, and (36b) will result, in this case in which UCC holds. Does UCC apply only to cases of overt movement, or to LF movement as well? The simplest, unmarked assumption of UCC as a constraint on the computational system would be that it applies to cases of double checking whether or not the checking is overt. To test this assumption consider VSO languages like Irish, discussed in Section 9. As we showed there, the D-feature of AGRS in Irish is weak, movement of the subject DP to AGRS and checking of the D-feature of AGRS only occurring at LF, thus accounting for the VSO order. We also argued that Irish is an OI language, with the SVO order for root clauses possible in the OI stage with a non-finite verb. Thus AGRS or TNS must be missing in the OI structures as we argued. This result follows from UCC so long as UCC rules out cases of double Dchecking even if one (or more) of the checking movements is covert. Thus the simplest unmarked assumption - that UCC is oblivious to the 'overtness' of the checking movement - seems correct.34 11.2. The interface nature of the requirement for AGR/TNS Thus we have derived the AGR/TNS Omission Model from the Unique Checking Constraint.35 That is, we have shown that UCC derives properties (33a-d). Since we know that ATOM is satisfied empirically over a wide range of developmental phenomena, UCC is a good candidate for a developmental constraint on early grammar. some detailed discussion relating to Dutch morphology and development, see Wexler et al. (1998). Also note that we would expect a kind of default agreement to be used in languages which have such (i.e. where certain person/number combinations weren't specified on some agreement morphemes) even when an 'infinitive' isn't predicted. Thus in French, if the third person singular agreement morpheme isn't specified with agreement features it will appear when AGR is omitted, rather than an infinitival. Such phenomena have been observed by Ferdinand (1997). 34 The fact that UCC applies to covert movement as well as overt movement is an argument against a 'processing' or 'resource limitation' account of UCC. Why should processing restrictions apply to covert movement? I know of no processing results - in adult or child language - which would argue that processing limitations apply to covert movement. 35 Borer and Wexler (1992) argued for the Unique External Argument Prota-Principle (UEAPP) in very early child grammar. UEAPP says informally that a subject may only be the subject of one verbal element (so that the subject may not be the subject of an auxiliary and a participle, for example. In some ways, UCC is reminiscent of UEAPP, thought stated in current syntactic terminology; UCC says a subject (i.e. a subject's D-feature) can't check twice. Details differ between the two proposals, it would be useful to see if they could be integrated so that the phenomena that UEAPP explains (different from the ones discussed in this paper) could be understood in UCC terms.
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Before going on in the next section to see how UCC also derives the crucial NS/OI (33e), we should discuss some of the properties of UCC and how it may be implemented in the grammar. First, I have stated UCC in one natural way given current Minimalist (checking) theory, which works in deriving the OI stage (the ATOM). Namely, the D-feature on DP can only check once. However, there are a variety of other ways of stating UCC which could also derive ATOM, following the leading idea that it is the double checking/movement process which causes a functional category to be omitted, so that convergence takes place. Perhaps in the OI stage, subject DP's can only check once, no matter which feature is being checked, and the 2 D-feature checking is only a special case. Or perhaps if checking isn't the right mechanism to state UCC, there is some other way of stating the constraint. Perhaps we should state that a subject (or some other DP?) can only move once, not twice or more, so that ATOM derives from the inability of the DP to undergo two movements, first to TNS and then to AGR. Such a proposal might have different empirical consequences than the constraint against double-checking, depending on whether DP's move for reasons other than D-checking. Since Chomsky (1995, Chapter 4) proposes that wh-movement is also motivated by D-checking, it's not clear what non-D-checking-motivated movements there are. Suppose that some movements, such as scrambling, topic-movement, etc., are motivated by particular semantic features rather than by the checking of a D-feature, though this is far from clear (after all, topicalization is close to wh-movement, and scrambling is usually thought to involve some 'specificity' feature, and D is the home of specificity). If there are such non-D-motivated movements of DP, then a constraint against double movement should prevent topicalization, after a single movement to AGR or to TNS. Thus Italian children in the OI stage should not allow topicalization, although they don't have OI's (as we later derive). There will be a variety of other consequences, but there is no room here for the careful syntactic analysis that would be required to attempt to distinguish consequences of a single movement hypothesis from the single checking hypothesis that I present. There are probably other ways of implementing UCC, depending on syntactic theory and, crucially, on what further empirical cases it is applied to. Further empirical investigation of children's grammars will be crucial in determining the best way of implementing UCC. For the moment the way I have stated UCC (as a constraint against double checking) works for the OI stage. Note that UCC applies to DP's in general, and not just to subjects. Thus UCC will apply, for example, to direct objects that have to undergo double movement/checking. Hagstrom (mss.) has shown that UCC in fact applies to cases of double movement/checking of direct objects in child Korean (in the OI age range), deriving the existence of word order errors involving the object and negation. To the extent that the UCC predicts the properties of the OI stage and applies also to constructions which don't involve the grammatical subject and associated (AGRS, TNS) INFL projections, it will turn out that the explanation for the OI stage cannot be found in a child deficit concerning the particular subject-related INFL projections. Rather, the explanation will be broader based, affecting the computational system of
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the syntax in more general ways, although the system of verbal morphology and its associated (subject) specifier has been the focus of research to date. At the moment the question remains open, but the general direction of research investigation is clear. What is the nature of the child 'deficit' that causes UCC? There are various possibilities. On the one hand, it may be that the child's syntax simply states UCC, thus causing a more restrictive syntax than the adult UG has. This could be true to the extent that the child only allows the single-checking against INFL, and doesn't allow double checking. Consider this possibility for the moment.36 The child has a more 'restrictive' syntax than exists in adult UG, since grammatical (convergent) possibilities in adult UG are ruled out in the OI child (i.e. double-checking derivations, which converge in adult UG are ruled out as non-convergent in Ol/UCC-constrained syntax). This restriction is thus an instance of Borer and Wexler's (1992) UG-Constrained Maturation, the defining characteristic of which is that the child's possible grammatical representations are a subset of UG representations, with 'wild' (nonUG compatible) representations ruled out. Thus the move from OI syntax to adult syntax is a case of pure 'growth', with representational possibilities added over time, but no non-UG possibilities ever allowed. How is this possible, given that we have assumed that the OI child - unlike the adult - allows simple clauses with either AGR or TNS missing, i.e. clauses with the structure (39)? There are various possibilities. One reasonable analysis seems to be that the OI child knows that AGRS and TNS are required in simple clauses, but that UCC forces one of them to be omitted if the derivation is to converge. Recall that the presence of AGRS and (finite) TNS in a root clause does not appear to be a consequence of the computational syntax of UG. There is no 'principle' of Minimalist Syntax, say, that forces the existence of AGRS or TNS. Consider the most 'motivated' projection - TNS - most motivated because it is motivated on semantic or interpretive grounds. But exactly what is the 'principle' that forces the existence of finite TNS in a root clause? Assuming that it is something 'interpretive' (the best guess), some kind of 'anchoring' (as in En£, 1987), by definition this 'interpretive' property (a property of the interface between syntax and the 'conceptual' system) does not play a role in 'convergence', a formal/syntactic/computational property. Thus OI clauses converge; their oddness is due to something interpretive/conceptual. In particular, the structures (and the associated derivations) in (39) converge, so far as can be told from current syntactic theory. Thus the OI child has ruled out as non-convergent some UG-convergent structures (double-checking ones such as (34)), and the price she pays is that in order to obtain a close-enough match that converges in her grammar she has to assume some interpretively-odd (i.e. interfaceodd), but convergent structures (like (39)). On this view we can maintain that all structures which converge for the child also converge for the adult.
36
We will return to the 'optionality' that seems to be inherent in the OI stage, since finite sentences are also grammatical in this stage, and discuss the question of whether UCC has to be seen as an 'optional' principle. The answer will be no.
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(40) UG-Compatible Convergence (UGCC) If a structure converges in child syntax, then it converges in UG. UG-Compatible Convergence is a refinement of UG-Restricted Maturation, making clear that what is specifically disallowed in child grammar is a derivation which is looked on as grammatical in the computational system of the syntax (i.e. convergent) for the child if that derivation is not looked on as grammatical in the computational system of the syntax (i.e. convergent) for the adult. The intention of (40) is that 'wild grammars' - those which allow structures to converge which UG doesn't allow to converge - are not permitted in child grammar.37 It is thus gratifying that a property (UG-Restricted Maturation) which has been taken to cover so much of grammatical growth can also be implemented in a natural way to cover the large range of empirical properties discovered about the OI stage. However, we should ask what it means for the 'interpretive/conceptual' properties which require AGR and TNS to be violable by the child. 11.3. Minimize violations Note that we don't have to assume that the child doesn't know that AGRS and TNS are required in simple declarative clauses (except for exhortatives, etc.). The child could very well know this property, but be willing to sometimes violate it in order to get a convergent derivation, when this is demanded by UCC. We can assume (41): (41) Minimize Violations (MV) Given an LF, choose a numeration whose derivation violates as few grammatical properties as possible. If two numerations are both minimal violators, either one may be chosen.38 Let's assume that Minimize Violations applies in child grammar.39 Suppose the child's grammar attempts to derive sentence (36a). Suppose the numeration (the 37 UGCC is not a principle of grammar, adult or child. Rather it is a (hypothesis about a) property of child grammars. As an anonymous reviewer points out, UGCC will have to contend with many problems. For example, English-speaking children often produce questions without inversion. How do these converge for adult grammar? We would have to ask whether non-inversion structures converge for the child. If they do, we would have to ask what their structure is, and whether with this structure they converge in UG. I am not prepared to give a discussion of this topic here, but the answer isn't obvious without investigation. 38 The idea is that numerations are chosen so as to yield an LF. Presumably, say, TNS is required for a certain LF, but when TNS (and AGR) is chosen UCC is violated. An enumeration without TNS may yield the same LF (with tense/time filled in from 'context' but may violate whatever property requries TNS in a root structure. For a different view on how competing numerations may enter into the explanation of the OI stage, see Schiitze (1997). 39 Putting off the question of whether Minimize Violations applies in adult grammar; it very well might, though with a slightly different grammar (e.g. no UCC) the consequences will be different in certain cases.
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words which enter into the sentence) include the words in (36a), with the verb likes as one member of the numeration set. This sentence doesn't converge given UCC, since (37) results, and (37) has an unchecked (-Interpretable) D-feature. To derive (36a) so that no D-feature is left would require a violation of UCC, but no violation of the interpretive/conceptual property which requires AGRS and TNS. On the other hand, suppose the child's grammar attempts to derive a sentence beginning with the numeration of the words in (36b), which are identical to (36a) except that the verb is run. Deriving this sentence (as in (39a or 39b), with AGRS or TNS missing, involves no violation of UCC but does involve a violation of the interpretive/conceptual property which requires AGRS and TNS in a sentence. Given that both numerations (from 36a or from 36b) are both minimal violators (one violation in each case), either representation is chosen as the grammatical representation. Thus the 'optional' behavior in the OI stage. In adults, there are no grammatical properties violated in the derivation of (36a), and one violation of a grammatical property (AGRS or TNS is missing) in the derivation of (36b). Thus (36a) is the only possible sentence. In the OI child, on the other hand, there is one violation (of UCC) in the derivation of (36a) and one violation (that AGRS or TNS is missing) in the derivation of (36b). Thus either (36a) or (36b) may be chosen in OI grammar (one governed by UCC), since they are both minimal violators. 'Optionality' in the OI stage thus is a consequence of a tie between two representations, each of which violate one property of child syntax. It happens that one of those properties (the requirement that AGRS and TNS appear) is also a property of adult syntax. But UCC is not a property of adult syntax. Therefore we get slightly different systems in the child and adult, both being consequences of the same fundamental system (with MV, etc.).40 40
The implementation of UCC via MV predicts, on the simplest assumptions, that finite sentences such as (36a) have the same grammaticality status as the OI sentences (36b). Since both finite and OI sentences are produced in the OI stage, this assumption seems as if it is confirmed. In general it is difficult to tell from the proportions of finite and OI sentences produced whether one is 'more' grammatical than the other. The basic facts are that the proportion of finite sentences increases over time in the OI stage, with the earliest stages showing extremely few finite sentences. Wexler (1990ff.) suggests that it is conceivable that there is a (very young) stage during which only OI's are produced, but the data is too scanty to determine whether this is true, in general. So, if proportion of finite sentences were to determine which form were 'more' grammatical, we would have to say it changed over time. So the production data are consistent with an equivalent grammaticality status for finite and OI sentences. The one potentially testable prediction of the MV view might be that, if grammaticality judgment tests were conducted, finite sentences would be judged to have the same grammaticality status as OI sentences, namely grammatical. The only judgment data about the OI Stage of which I am aware is on English. Rice et al. (in press) have shown that English-speaking children in the OI stage judge OI sentences (e.g. (i)) to be more grammatically than sentences with agreement violations (e.g. (iii)). Grammatical (finite, with no agreement violation, e.g. (ii)) sentences are judged somewhat better than OI sentences (i), but the OI sentences are closer to the grammatical (ii) judgments than to the ungrammatical (iii) judgments. (i) Mary go/going (ii) Mary goes/is going
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Notice that both numerations 'converge' for the adult. One is simply the adult structure. The other involves no syntactic violations, and is therefore convergent, with the functional category (AGRS or TNS) missing. That is, nothing about the structure is non-convergent so far as can be told from current syntax. (Of course we have to assume that if AGRS is missing, no case feature is selected from the lexicon on the subject DP.41 But exactly such an assumption of 'no case filter' is what Minimalism requires, as Chomsky (1995: Chapter 4) discusses). The Minimize Violations view of the UCC appears to substantiate work in other areas of linguistic development. Babyonyshev et al. (1994) investigate the growth/maturation of Argument-chains (A-chains) (Borer and Wexler, 1987, 1992) by applying the theory to the Genitive of Negation in Russian. Borer and Wexler (1992) predicted that children who don't find A-chains grammatical will give an unergative analysis (with subjects directly generated in subject position), to unaccusatives. Babyonyshev et al.'s (1994) experiment shows that children before five sometimes give an A-chain analysis to unaccusatives and sometimes don't (i.e. the same child does one or the other). They explain this 'optional' result by assuming that children have a *A-chain constraint (i.e. nontrivial A-chains are ungrammatical) in their syntax but also know UTAH, an interpretive/interface condition, which predicts that unaccusatives must generate their subject in object position. Thus any unaccusative for a *A-chain child will violate either *A-chain, if it is given an unaccusative analysis, or will violate UTAH if it is given an unergative analysis. Thus either of these analyses - unaccusative or unergative - can be chosen; they are equivalent with respect to the number of violations. Thus it may turn out that the MV view, with violation of one or the other constraint possible, is a general explanation for what appears to be 'optional' behavior in children which is obligatory in adults. The Minimize Violations implementation of the UCC thus explains in a natural way the 'optionality' property of the OI stage without recourse to mechanisms of optionality that don't exist in the adult grammar. The optionality is the result of a stronger UG constraint than exists in adult UG, but not from the result of a fundamental difference in computational syntax, such that optionality is a property of OI grammar but not of adult grammar.42
(iii) Mary am going/I goes Thus the results are somewhat equivocal on this issue. Although clearly OI sentences are more grammatical than are OI sentences, it's not absolutely clear whether finite, agreeing sentences are more grammatical than are OI sentences or whether they are equivalently grammatical. The ideal result given the point of view just presented would be for OI sentences to be as grammatical as finite agreeing sentences, at least during the heart of the OI stage. This may yet turn out to be true. Experiments in other OI languages would be extremely useful in this regard. It would be good to compare finite agreeing sentences against sentences which don't violate UCC, and violate no other constraint, but since simple grammatical sentences, on the syntactic view that we have presented, always involve a violation of UCC, it is not clear how to do this. 41 If NOM case, say, is selected, then it won't meet the requirement which pairs AGR with it. 42 The MV view of UCC seems to imply that computational constraints (like UCC) and interpretive/interface constraints (like the requirement for AGR/TNS) have the same status in child grammar, since either constraint may be violated if one of them has to be violated. Suppose we wanted
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11.4. Interpretable features? UCC (35) simply assumes that double-checking cannot take place grammatically in the OI child. Is it possible to derive UCC from more fundamental assumptions? A potential avenue for exploration focuses on what it is in UG which allows or forbids double-checking at all. Chomsky (1995) assumes that features can be divided into interpretable features (those which must stay around in a derivation till LF) and uninterpretable features (those which don't stay around until LF because they play no interpretive role). Interpretable features don't delete after checking; after all, they must show up at LF. Thus interpretable features can (and often do) check more than once. Uninterpretable features delete after checking, so they can check only one time.
to attempt an implementation of the OI stage which in fact did treat purely syntactic/computational constraints as non-violable by the child, and interpretive/conceptual/interface constraints as violable if necessary to maintain the non-violation of the computational system. We could assume (i) instead of MV (41). (i) Preference for Convergence (PC) Given a choice between a convergent derivation (in child syntax) which omits an interpretively motivated functional projection and a non-convergent (in child syntax) derivation which includes the projection, choose the convergent derivation. The Preference for Convergence interpretation of UCC thus chooses an OI representation, inw hich AGR or TNS is omitted, over a representation in which double-checking of D is permitted. Thus PC implies that finite sentences are always ungrammatical for the child, the OI sentence always being preferred. Thus we would have to specify that UCC optionally applies, an unexplained stipulation at odds with the spirit of Minimalism. One possibility is that UCC is not a syntactic/computational constraint after all, but is the consequence of 'processing' problems in the child. For some reason, the OI child's processing system can't always check a feature twice, or can't always move the same constituent twice, or has some related property that makes the derivation of finite sentences complicated. We would also have to assume that the processing system is subject to 'optional' behavior in a way in which the syntactic system is not. This is a possible explanation, but we should be careful before following the time-honored (but rarely supported) route of assuming that all child deviations are due to the processing system. See Wexler (in press) for arguments against this being any kind of preference, and also see Grain and Wexler (in press) and Grain and Thornton, (1998) for the Modularity Matching Model, which argues that the general spirit of linguistic theory as well as empirical results imply that child processing systems should be looked on as having the same essential properties as the adult systems. There is no independent evidence for the processing 'difficulty' of double-checking, and children in the OI stage show excellent ability to carry out many operations in a sentence (for example, to assign case and agreement correctly). There is no empirical evidence or theoretical analysis of children's processing abilities/difficulties which would support this claim. It might be just another case of ignoring the problem. On the other hand, it is a possibility that UCC is due to some kind of processing difficulty (of a highly special kind, yet to be discovered), a claim which is difficult to evaluate empirically given the underdeveloped state of processing theory and data in children. The PC view implies that finite sentences are derived by UCC not applying and are therefore totally grammatical, whereas OI sentences violate an interpretive/interface constraint. Thus finite sentences should be judged as more grammatical than OI sentences. These predictions are different from the predictions made by the MV without PC view, discussed in a previous footnote. As I discussed in that footnote, the empirical results are not completely clear. Also, if 'processing' is the explanation for the UCC and its optional application, then it is not clear how processing will affect grammaticality judgments.
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Case features, for example, having no interpretive role, are [-interp], and don't stay around until LF, deleting after checking once. Thus more than one NOM can't be checked by the same INFL (I put aside questions of multiple specs, as in Ura, 1996). D, on the other hand, does play an interpretive role, thus is [+interp] when it appears on a DP (as we pointed out before, D is -Interpretable when it is on a functional category like AGRS or TNS). A D-feature thereby can check more than once. An example is a raising construction, as in (25), repeated here as (44). The subject DP Mary has a D-feature which first checks the D-feature of the -fin INFL in the embedded clause. This D-feature (since it is [+interp] does not delete after this checking. The subject Mary then raises to the higher +fin INFL and the same D-feature on Mary checks the D-feature on this INFL, thus double-checking. (44) Mary INFL(+FIN) seems [ e t to INFL(-FIN) [VP e2 like it here] Another example is the derivation of a finite sentence that we have assumed in (34), repeated here as (45). The DP raises to TNS, and its D-feature checks off the D-feature of TNS. The D-feature on DP, being [+interp], does not delete. The DP then raises to AGRS, and the same D-feature on the DP checks off the D-feature of AGRS. Thus double-checking, by a D-feature. (45) a. AGRS[D] TNS[D] [ VP DP V...] Pi AGRS0 Uspt, TNS0 [ VP ti V...]]] Thus on the view of UG in Chomsky (1995), a feature can check more than once if and only if it is [+interpretable]. Since the UCC forbids a double-checking in the child where it is allowed in the adult, this immediately suggest the following hypothesis to explain why UCC holds in the OI child. (46) For the OI child, D can not only be [+ interp] (as it is for adult) but also [-interp], as it is not for the adult. Consider a finite sentence, such as (34)/(45). This sentence requires the D-feature on the subject to check twice, against TNS and then against AGRS. If a child chooses a [+interp] D, the derivation converges, as it does for adult. Thus finite sentences are grammatical for the OI child. Suppose, on the other hand, the child chooses [-interp] D on the DP, as is allowed by (46). Then the D-feature of DP deletes after checking one INFL category. Thus in (34)/(45), after checking D on TNS, the D-feature of the DP deletes, and no further checking can take place. Thus the D-feature of AGRS remains unchecked, as in (39). Thus the derivation crashes. But if the child omits AGRS or TNS, as in (39), one checking of the D-feature on the subject DP is necessary. The ([-interp]) D-feature on DP deletes after checking the D-feature on the one INFL category in (39) (whether AGRS or TNS), but it doesn't cause the derivation to crash, since no noncheckeD-features remain.
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Thus the effects of UCC can be derived via a misunderstanding of the interpretive conditions in D. The child has to consider D as [-interp] sometimes. This might be the result of a possible interface/pragmatic deficit. Children in the OI stage often delete determiners,43 although it isn't clear what relation there is between determiner omission and interpretability.44 Furthermore, there is evidence (Maratsos, 1976; Karmiloff-Smith, 1979; Hickmann et al., 1996; Kail and Hickmann, 1992 among others) that young children often use the instead of a. Thus children don't necessarily interpret specificity correctly, possibly not understanding that D is always interpretable. Det is the home of specificity (Or of old/versus new information).45 Thus this may also be suggestive evidence that children don't understand the interpretive features on DET.46 If the effects of UCC are due to a misunderstanding of the interpretive characteristics of D (46), then we expect that double-checking only of D will be ruled out by the OI child. We don't know enough about other properties to test this assumption at the moment. At any rate, we should consider both UCC as a fundamental constraint on OI grammar and the derivation of UCC from flaws in the knowledge of interpretation of features as potential hypotheses as to why ATOM holds in the OI stage. 12. The derivation of NS/OI We have seen how the ATOM and raising of subjects even in OI's follow from the Unique Checking Constraint, on the assumption that D-checking as the motiva43
Though in general determiners in OI languages are not deleted as often as TNS/AGR is deleted. Enough hasn't been studied about this topic but there's some good quantitative evidence about English in Rice and Wexler (1996 ) and in Dutch in unpublished work I am conducting with Jeannette Schaeffer and Gerard Bol. 44 Suppose determiners are licensed strictly through their interpretable features. If a determiner is treated by a child as [-interp] there may be no further licensing property for the determiner and it is therefore omitted. Compare this situation with Case, which is licensed by formal features. NOM case, for example is licensed by AGRS. As discussed earlier (and see Schiitze and Wexler, 1996a,b), we know that NOM is almost never deleted if AGRS appears. Of course the speculations in this footnote must be supported by an understanding of the licensing conditions for determiners. Another way of thinking about the assumption that kids think D can be [-interp] is that they are sometimes treating D as pleonastic in some sense, a formal feature without interpretation. 45 Hoekstra et al. (1996) have attempted to relate Determiners and TENSE as has Wexler (1996), but the models presented quite clearly different than the one presented here. In those models it's the semantic properties of DET and TNS that are compared (having to do with particular features, for example number features in Hoekstra et al., and referential features in Wexler). The UCC, on the other hand, involves a particular computational constraint on checking. 46 Wexler and Chien (1985) and Chien and Wexler (1990) and many other references argue that 'Delay of Principle B' effect is due to pragmatic conditions on TNS. Avrutin and Wexler (1995) and Avrutin (1992) relate the definite for indefinite errors mentioned above (the instead of a) to the Principle B effect. Thus the OI stage might be tied together with the Delay of Principle B phenomenon. A problem for this analysis is that the Delay of Principle B effect lasts much longer (to around 5) than does the OI stage. Thus although there may be a pragmatic/interpretive basis for both late developments, it is unlikely that is exactly the same pragmatic/interpretive deficit.
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tor for the Extended Projection Principle. It remains only to show that NS/OI - the puzzling generalization that the OI stage exists if and only if the adult language being developed is an INFL-licensed null-subject language - follows from UCC. At first sight it seems that UCC is in no position to derive NS/OI. For UCC simply disallows the D-feature on DP to check twice, to check two functional categories, thereby forcing the omission of AGR or TNS, with its associated D-feature. Why shouldn't this apply in all languages, since we assume that the hierarchy of functional categories is identical in finite clauses in both null-subject and non-nullsubject languages. It turns out, however, that the nature of null-subject languages is exactly such that UCC won't apply. Recall that we would are maintaining VEPS, so that all relevant parameters are set correctly in both null-subject and non-null-subject languages. Moreover, we make the unmarked assumption that development proceeds equivalently with respect to constraints that grow in all languages. Thus UCC holds in null-subject languages like Italian at a given age just as much as it does in French or German or English. Why then doesn't UCC force Italian children in the OI age range to drop AGR or TNS, thus displaying OI phenomena? The crucial reason is (47): (47) In INFL-licensed null-subject languages, AGR is not D In null-subject languages like Italian, intuitively and traditionally AGR is D; it doesn't need D, which is what the D-feature on AGR means, that AGR needs to be checked against some subject D-feature. The traditional idea, and what still underlies the analysis of null-subject grammars in contemporary syntactic theory (e.g. Rizzi, 1994a,b; Zagona, 1982) is that AGR is pronominal or nominal in some sense. The pronominal nature of AGR in null-subject languages is what makes a subject unnecessary. The strength (pronominal nature) of AGR is what makes null-subject grammars like Italian possible. AGR itself licenses or identifies (we won't distinguish these notions here) the null-subject. Thus in null-subject grammars, AGR is pronominal. How is this to be characterized? Essentially pronominals are D's. I suggest that the +D-feature is an extremely natural way to characterize AGR in a null-subject language, capturing within Minimalist Theory the traditional idea. But if AGR is +D, it can't be D, that is, it can't have the requirement that it needs a D-feature to check it. AGR is D, it doesn't need aD. Thus (47) simply states a property of null-subject languages and in fact we should state the property more fully as (48): (48) AGR is D in a language if and only if the language is an INFL-licensed nullsubject language47 47
In (47) and (48) I don't commit to whether AGR is itself +D when it is not -D; this is a matter of execution which doesn't seem crucial here; probably the +D nature of AGR is a natural way to implement the hypothesis.
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When AGR is D, then the subject must raise to it so that the D-feature of the subject can check off the D-feature of AGR. When AGR is not D, there is no D-feature on AGR which must be checked off by the subject. Therefore AGR does not have to attract the subject, at least for reasons of checking off D.48 We have no reason to think that the D-feature doesn't exist on TNS in Italian as well as in the non-null-subject languages. So, in contrast to finite clauses in the nonnull-subject languages, which have the pre-movement/checking analysis in (34a) (repeated as 49a) and the final representation in (34b)(repeated as 49b), finite clauses in null-subject languages have the pre-checking analysis in (50a) and final representation in (50b). (49) Finite clause analysis in non-null-subject language a. AGRS[D] TNS[D] [ VP DP V...] b- UoRSpDPi AGRS0 [TNSPti TNS0 [ V pt, V...]]] (50) Finite clauses analysis in null-subject language a. AGRS TNS[D] [ VP DP V...] b. UGRSP AGRSo tiNSpDP, TNS0 [vpt, V...]]]49 Since there is no D-feature on AGRS in null-subject languages, the subject DP doesn't raise to AGRS to check off a D-feature. (See the last footnote for the question of whether the subject raises to AGRS at all. Whatever the status of this question, it is clear that it is not a D-feature that drives the movement in null-subject languages.) Rather, the subject DP only raises to TNS to check off the D-feature on TNS. Now suppose UCC applies. As we have seen in non-null-subject languages, since double-checking can't take place, we would wind up with (37) (repeated as (5la) instead of (49a)). The D-feature on AGRS is unchecked and the derivation crashes. On the other hand, in a null-subject language like Italian, there is no D-feature on AGRS; thus UCC only applies vacuously. UCC says that DP can't check a D-feature a second time, but since there is no second D-feature in a null-subject language, UCC doesn't change the derivation. The output representation (51b) is the same as the adult (non-UCC-constrained) output representation (50b). Since there is no uncheckeD-feature in (51b), this representation doesn't crash. 48
I won't work out the detailed syntax of the null-subject here, in particular the question of whether the subject raises to AGR for other reasons. But the proposal I have made in the text seems to me quite likely to be on the right track, given current work on null-subject languages. Let's assume the empty subject (pro) is in Spec,AGR, not because it has been attracted by some -D-feature, but rather for reasons of identification; pro is deficient in features, which must check against AGR. What about lexical subjects? Since they have agreement features which must match AGR, haven't they raised to AGR? Barbosa (1996) has argued that lexical subjects in the null-subject Romance languages are in a higher position than INFL, presumably in some kind of focus-like position. So presumably these subjects have raised to this higher position to check off some kind of interpretive (focus-like) feature, not to check off a D-feature. Presumably a checking against a -D-feature of AGR is never a process in null-subject languages like Italian. 49 We ignore questions of verb movement, simply leaving the verb in situ in the representations so as not to complicate them.
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(51) Finite clause terminating representation constrained by UCC: a. Non-null-subject language *AGRS[D] [DP1 TNS [VP t; V...] b. Null-subject language AGRS [DP; TNS [VP tj V...] Thus, under UCC, the representation of a finite sentence in a non-null-subject language (5la) crashes, but in a null-subject language the representation of a finite sentence (51b) does not crash. Therefore whereas OI's become good representations in a non-null-subject language, they are not good representations is a null-subject language. Thus we have derived NS/OI. This derivation proceeds no matter which of the alternative implementations of UCC discussed in Section 11 we assume. For example, if we assume Minimize Violations (MV) we showed that in a non-null-subject language, the UCC-constrained representation of a finite clause ((37), (5la)) had one violation, UCC. And the alternative representation in which AGRS or TNS is missing has one violation. So that MV allowed either the finite or OI representation to be chosen. But in a null-subject language, the UCC constrained representation of a finite clause (51b) has no violations, whereas the representation in which AGRS or TNS is omitted has one violation. So MV selects the finite clause as the only grammatical representation. Similarly for the other implementations discussed. For example, if D can sometimes be [-interp] for a child, we assume that the same is true of a child developing Italian. It is just that the deletion of the D-feature after one checking will have no effect in Italian and other null-subject languages because D does not have to check a second time in these languages. What do we have to assume about the child to make this derivation go through? (52) a. The OI child knows the UG syntax of null-subjects (48) b. The OI child knows the correct parameter-setting for AGR in her language, i.e. whether AGR is D or not c. The OI child is subject to UCC, independently of the language being acquired (52a) is simply the assumption that the child knows a UG property, namely whatever properties implicate (48), the relation between a D AGR and the licensing of null-subjects by AGR. (52c) is the one assumption that we have made to derive the OI stage and the ATOM more generally. (52b) is an instantiation of Very Early Parameter-Setting; it simply assumes that the OI child knows the correct setting of this parameter (whether AGR is D or not). Not only is it thus an instance of the general hypothesis of this paper, but in Section 5 we gave some strong evidence that the null-subject parameter is correctly set in the OI age. Thus the assumptions in (52) essentially come for free. NS/OI is forced; if it weren't true we would have something to explain. Crucially, UCC, a developmental constraint, something which the child grows out of, applies to the child universally. It only appears to not apply in null-subject languages, because of the nature of the
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language itself, as instantiated in a parameter value, something which the young child knows. Crucially, the child is the same with respect to underlying developing constraints, the UCC in this case, whether the child is speaking a non-null-subject language with OI's like French or German, or a null-subject-language without OI's, like Italian or Spanish. UCC holds universally. Moreover, the correct parameter-setting has developed universally; it is just not a particular parameter-setting which makes the effects of the developmental constraint (UCC) vacuous. This is exactly the kind of result we should expect; the only thing that has to be learned is a parameter-value, and it is learned, early and well. A part of the genetic program - the UCC- applies in interaction with the parameter-setting to yield what appear to be very different phenomena - a large proportion of OI's in non-null-subject languages, and no (or very few, presumably due to noise) OI's in null-subject languages. Such a result makes us think we are on the right track. We may ask further questions. Since we assume that UCC actually holds in nullsubject languages, though it applies vacuously to the simple finite sentence case, can we find any structures in null-subject languages to which UCC should apply nonvacuously? Consider a structure in Italian with an auxiliary verb, such as the passato prossimo, the periphrastic perfect tense construction, the equivalent of Mary has laughed (meaning Mary laughed) or Mary is come, (meaning Mary came). Belletti (1990) has argued that auxiliaries in Italian head their own phrase. Thus we would expect such a structure to look like (53). (53) AGRS TNS[D] AUX[D] [ VP DP V...] Exactly where the AUX is in (53) with respect to the INFL categories AGRS and TNS isn't important for our purposes, thus probably it starts out below them. But what is crucial is the assumption I have made in (53) that AUX (like TNS but unlike AGRS) has a D-feature. The EPP, which forces movement to TNS, will force movement through an AUX if one exists. Whatever licenses/motivates the [D]-feature on TNS should do the same for an AUX; it 'needs' a subject, i.e. a DP, i.e. it has a [D]-feature. In the adult grammar of Italian, then, DP will first be attracted to AUX, checking off AUX's D-feature and then the DP will be attracted to TNS, checking off TNS's D-feature. But note that two checkings of the D-feature of DP are necessary in the he derivation that applies to (53); first against AUX, then against TNS. Thus the derivation of (53) will violate UCC, unlike the derivation of a simple finite sentence with only a main verb (50), which only has one D-feature. Thus (53) will crash in OI stage Italian (i.e. Italian constrained by UCC) even though OI's are not produced instead of finite main verbs. How can (53) be fixed so that UCC isn't violated? The simplest possible change seems to be to omit AUX.50 50
An alternative is to assume that AGR or TNS is omitted in (53) given UCC and that no auxiliary may then be spelled out given the morphology. I am not sure how to empirically distinguish the alternatives. At any rate, various possibilities converge on the omission of the auxiliary as the way to satisfy UCC.
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For then the sentence will have the representation like that of a finite main verb (50) even though a participle will exist in the sentence instead of a finite verb. Thus UCC predicts that auxiliaries will be omitted in Ol-age Italian. Exactly this occurs, as has been shown in Lyons (1997). Namely, a substantial proportion of auxiliaries are omitted in Ol-age Italian. Thus despite the fact that Italian is not an OI language in the sense of root infinitives appearing instead of finite main verbs, it does display another property of OI languages - auxiliary omissions. And this is exactly the property that UCC predicts Italian should exhibit. 13. Conclusion: On the seamlessness of linguistics and psycholinguistics In this paper I have argued that when something in syntax is learned (a parameter value) it is learned very early. Developmental constraints often take much more time to work themselves out. There is no reason to think that it is learning - experiencedependent properties - that are the cause of different structures used by children. Rather, the genetic program underlying language growth is the cause of many (most? all?) of these structures. Children set parameter values correctly at the earliest observed ages (VEPS). Moreover, they are masters of inflectional morphology, at least with respect to the central cases that have been investigated (VEKI). What takes more time is for oversevere constraints on the nature of UG to be developmentally/genetically relaxed. The OI stage contains linguistic structures which at first sight look strikingly different from adult structures. Deeper analysis, however, suggests that it is the result of one extra, more severe constraint that UG has - the Unique Checking Constraint. The analysis presented predicts what have appeared to be some serious difficulties for the analysis of the OI stage, namely, that subjects of OI raise, that subjects of OI's can receive NOM case, and most strikingly of all, that many languages do not undergo the OI stage. All these properties are seen to follow from UCC and from interesting conclusions drawn in contemporary syntactic theory - especially about the D-motivation for the Extended Projection Principle. In this regard the theory of linguistic development and the theory of syntax have drawn closer together, depending on the same particular assumptions, a very satisfying development. The study of language acquisition turns out to have the capacity to add to linguistic theory - the central questions of the nature of UG and of its development. It seems to me that the actual study of linguistic development now makes it clear that it is to underestimate this capacity of language acquisition to add to theory if one assumes that acquisitional studies are done simply to 'confirm' adult analysis or to show that the child 'has' UG. In my opinion, the theory of linguistics has much to gain by incorporating the problems of acquisition directly; there are already a number of real examples. And acquisitionists must confront the possibility of proposing changes in linguistic theory on the basis of developmental results. Of course, the proposed changes must be based on clear analysis, integrating child and adult data. As a methodological lesson, it seems to me that it might be suggested that the most interesting places in the current state of the art to look at children's language is
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where the child shows different behavior from the adult, where the child appears to have different grammaticality judgments. This is where we have a good chance of learning something about the particular nature of the genetic program underlying UG. This is especially true since we have every reason to believe (VEPS, VEKI) that it isn't learning that is responsible for the difference. One may distinguish two views in the history of Psycholinguistics, even in generative grammar-influenced research. One is the view of generative grammar, which says that performance systems contain grammars. The second view is what I call the Independence view, which I attribute to (at least) Fodor et al. (1974) . The Independence view says that performance systems don't contain grammars (rather performance systems are based on 'strategies'). Independence means that results in psycholinguistics. don't influence analysis in linguistic theory and conversely results from the study of adult language don't influence developmental psycholinguistics. Independence thus has the advantages of allowing each field to go about its business without worrying about the other field. It does simplify research by allowing a related field's results to be ignored. Perhaps for this reason Independence seems to me to have been the dominant view in generative grammar-related psycholinguistics. Despite this seeming advantage, in my view, Independence is the less fruitful view. The fields can influence each other and should. The trade-off for the greater complexity created by having to integrate different kinds of methodologies and domains of phenomena is the greater insight obtained by bringing to bear the different results from both fields, thus constraining the problem in useful ways. In this paper I hope to have gone a small way toward showing that results in developmental psycholinguistics are relevant in detail to the study of the nature of language.
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Lingua ELSEVIER
Lingua 106 (1998) 81-112
Aspects of root infinitives^ Teun Hoekstraa, Nina Hyamsb'* 8 b
Leiden University/HIL, PO Box 9515, 2300 RA Leiden, The Netherlands Dept. of Linguistics, UCLA, 405 Hilgard Avenue, Los Angeles 90025, USA
Abstract This paper discusses the phenomenon of root infinitives (RIs) in child language, focussing on a distributional restriction on the verbs that occur in this construction, viz. event-denoting verbs, as well as on a related aspect of interpretation, viz. that RIs receive modal interpretations. The modality of the construction is traced to the infinitival morphology, while the eventivity restriction is derived from the modal meaning. In contrast, the English bare form, which is often taken to instantiate the Rl-phenomenon, does not seem to be subject to the eventivity constraint, nor do we find a modal reference effect. This confirms the analysis, which traces these to the infinitival morphology itself, which is absent in English. The approach not only provides a precise characterization of the distribution of the Rl-phenomenon within and across languages; it also explains differences between the English bare form phenomenon and the Rl-construction in languages with genuine infinitives by reference to the morphosyntax of the languages involved. The fact that children appear to be sensitive to these distinctions in the target systems at such an early age supports the general thesis of Early Morphosyntactic Convergence, which the authors argue is a pervasive property of the acquisition process. Keywords: Syntax; Acquisition; Root infinitives; Eventivity; Modality
1. Introduction The phenomenon of root infinitives (RIs) in child language has received a lot of attention in the recent literature. There has been much debate over the distribution of the phenomenon both within and across languages, and also over the structure underlying RIs. In this paper we focus on the interpretive properties of RIs, an area which has not been very widely investigated. As we will show, there seems to be a con* The research for this paper was made possible through a grant from NWO (Dutch Organization for Pure Scientific Research) to Nina Hyams, and a UCLA Faculty Senate Grant. This support is hereby gratefully acknowledged. We thank the audience attending a presentation of this work at the University of Southern California, March 21, 1998, for their comments and questions. We also thank Carson Schutze, Neil Smith and two anonymous Lingua readers for their comments. * Corresponding author. Phone: +1 310 206 8375; E-mail:
[email protected] 0024-3841/997$ - see front matter © 1999 Elsevier Science B.V. All rights reserved PII: 80024-3841(98)00030-8
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straint on the aspectual nature of the verbs occurring in Rl-constructions, viz. only eventive verbs are allowed in such constructions, whereas stative predicates occurring during this same period typically require finiteness. We shall refer to this as the Eventivity Constraint (EC). Also, RIs typically do not get a deictic tense interpretation, but rather receive a modal interpretation. We call this Modal Reference Effect (MRE). Interestingly, both the EC and the MRE found in Dutch and other languages appear to be absent from early English bare V-constructions. The fact that English bare V-constructions show neither the effects of the EC nor seem to have modal reference suggests that these two properties are related, one of the points which we will argue in this paper. More generally, we will address the following questions: (i) What is the nature of the Eventivity Constraint? (ii) Why do RIs receive modal interpretations and how does this relate to the Eventivity Constraint? (iii) Why is English different? The paper is organized as follows. In Section 2, we introduce the Rl-phenomenon, and discuss its main properties as they have emerged from the recent literature. In this section we also discuss several analyses of the Rl-phenomenon, focusing on our own underspecification analysis of RIs (Hoekstra and Hyams, 1995, 1997). We show that various syntactic and distributional differences between RIs and English bare Vconstructions can be explained as effects of the different morphological systems. This proposal is part of a more general hypothesis concerning the relationship between the child's development of morphosyntax and his development of the interface or discourse conditions governing the expression of the morphosyntax, which we call Early Morphosyntactic Convergence. As we have argued elsewhere (Hoekstra and Hyams, 1995; Hyams, 1997), children readily converge on the specific morphosyntax of the adult target language, but have less restricted interface conditions than adults. In section 3, we present the empirical evidence for the EC and for the claim that RIs receive modal interpretations. In this section we also show how English child language is different in these respects from other child languages that display the Rl-phenomenon. In Section 4 we discuss the merits of another theory of RIs, the Null Modal Hypothesis (NMH), which might account for the modal interpretation of RIs. We conclude that although the NMH has a lot of explanatory potential, it meets a number of insurmountable empirical problems. Finally, in Section 5 we directly address the questions in (i) to (iii). We introduce our account of the modality of Rl-utterances, and we discuss the relationship between modality and aspect, showing how the EC is in fact an immediate consequence of the modality. Finally, we explain why English is different in these respects from the other languages that have been studied. We explain these interpretive effects in terms of the morphosyntactic properties of the respective adult languages, which also show a (limited) Rl-effect. In the conclusion we briefly discuss the interface differences between adults and children that allow children to have a more liberal use of RIs than adults.
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2. The Root Infinitive Phenomenon 2.1. Properties of Rh It has long been noted that children acquiring Dutch, German, Swedish, French and many other languages pass through a stage in which they use infinitives in root contexts - so-called root infinitives (RIs) (term due to Rizzi, 1994), as in (1). (1) a. Papa schoenen wassen. Daddy shoes wash-inf. b. Michel dormir. Michel sleep-inf. c. Thorstn das haben. Thorstn that have-inf. d. Jag ocksa hoppa da'r & da'r. I also hop-inf. there and there
(Dutch, Weverink, 1989) (French, Pierce, 1992) (German, Poeppel and Wexler, 1993) (Swedish, Santelmann, 1995)
Van Ginneken commented on the existence of RIs in Dutch child language as early as 1917, noting that such utterances had a modal reference. More recent investigation of a number of child languages shows that there are systematic patternings of finite and non-finite clauses in early stages. First, RIs appear in positions in accordance with the target grammar. In French, for instance, finite verbs appear to the left of the negative adverb pas, while infinitives appear to its right (Emonds, 1978; Pollock, 1989). Pierce (1992) shows that similarly, in French child language RIs appear to the right of pas while finite verb forms appear to its left, as in (2) (cf. also Meisel, 1990; Verrips and Weissenborn, 1992). (2) [+finite] Elle a pas la bouche. she has not a mouth Veux pas lolo. (I) want not water Marche pas. (she) walks not Ca tourne pas. that turns not
[-finite] Pas la poupee dormir. not the doll sleep-inf. Pas manger la poupee. not eat-inf the doll Pas casser. not break-inf. Pas tomber bebe. not fall baby (Pierce, 1992)
Note that the finite and non-finite forms in (2) occur during the same time period occurring side by side in the same transcripts, so that RIs cannot be treated as an earlier developmental stage. Table 1 below shows the form-by-position interactions obtained by Pierce. Similarly, various studies of Dutch and German and other V2 languages have shown that RIs appear in the position of infinitives (clause finally in Dutch and German, after the negative adverb in the Scandinavian languages), while finite forms appear in second position (German: Jordens, 1991; Meisel, 1990; Boser et al., 1992,
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Table 1 Finiteness and position of negation in French (Philippe) (Pierce, 1992)
Neg V V neg
Finite verb
Non-finite verb
11 185
77 2
Weissenborn, 1991; Poeppel & Wexler, 1993; Clahsen and Penke, 1992; Dutch: de Haan, 1986; Jordens, 1991. Swedish and Danish: Plunkett and Stromqvist, 1990). Data from the German child Andreas, presented in Table 2, is illustrative of this general finding. Table 2 Finiteness and position of verb in Andreas (Poeppel and Wexler, 1993)
V2-position Final position
Finite verb
Non-finite verb
197 11
6 37
Andreas corpus: Wagner, 1985; CHILDES, MacWhinney and Snow, 1985.
As discussed in Hoekstra et al. (1996), the Rl-phenomenon is not due to a lack of knowledge of the relevant finite morphology nor to a lack of knowledge of Spechead agreement requirements. When finite forms are used, agreement is almost always correct. Table 3 provides the frequencies of agreement errors occurring in finite utterances in several child languages. The number of such errors is under 4%, very low even by the most stringent acquisition standards. Table 3 Percentage of subject-verb agreement errors in early language Child
Language
Age
Simone Martina* Diana* Guglielmo* Claudia Francesco Marco Marti* Josep* Gisela* Guillem*
German Italian Italian Italian Italian Italian Italian Cat/Span Cat/Span Catalan Catalan
l;7-2;8 l;8-2;7 l;10-2;6 2;2-2;7 l;4-2;4 1;5-2;10 1;5-3;0 l;9-2;5 l;9-2;6 l;10-2;6 l;9-2;6
%Error
1732
1%
478 610
1.6% 1.5% 3.3% 3%
201 1410 1264
415 178 136 81
129
2% 4% 0.56% 3% 1.2% 2.3%
Source Clahsen and Penke, Guasti, 1994 Guasti, 1994 Guasti, 1994 Pizzuto and Caselli, Pizzuto and Caselli, Pizzuto and Caselli, Torrens, 1992 Torrens, 1992 Torrens, 1992 Torrens, 1992
1992
1992 1992 1992
(*Data available on CHILDES, MacWhinney and Snow, 1985; Martin, Guglielmo, Diana corpora, Cipriani et al., 1991; Marti, Josep, Guillem, Gisela corpora: Serra and Sole, 1992)
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Furthermore, RIs bear correct infinitival morphology, e.g. -en in Dutch and German; -er/ir in French, -a in Swedish and so on. The data just reviewed leads to the conclusion that RIs constitute a grammatical category in their own right in a number of child grammars, with properties that differentiate it from finite constructions. This conclusion will be further reinforced by evidence we discuss below concerning other distributional and semantic differences between RIs and finite verbs. Let us now turn to English. Wexler (1994) has argued that English speaking children also show an Rl-stage. Utterances of the sort in (3), where the verb is missing the 3rd person singular -s, are analyzed by Wexler as the English analogue of the RI. (3) a. Eve sit floor. b. Cowboy Jesus wear boots.
(CHILDES, Brown, 1973)
The evidence for Wexler's conjecture is obviously much less strong than the evidence from other languages. First, English lacks a clear infinitival ending. Moreover, in English there is no positional difference between finite and non-finite verb forms.1 However, by assuming that it instantiates the Rl-phenomenon, the lack of -s inflection in English finds an independently motivated explanation and it brings English in line with the other languages studied. An alternative for English might be to analyze utterances such as those in (3) as resulting either from a breakdown in agreement or from the dropping of the -s affix due to production problems. But neither of these suggestions is theoretically very compelling. Why would English children make agreement errors or drop finite morphology when children acquiring other languages do not? In fact, with regard to agreement, Harris and Wexler (1996) show that to the extent that this can be tested given the weak inflectional system of English, young English speaking children do not make agreement errors. Of 1352 sentences containing the first person subject / from the corpora of several English speaking children, only 0.02% occur with a verb bearing -s (e.g. / goes). Many more such errors would be expected if these children simply failed to respect Spec- head agreement requirements. On the other hand, an account in terms of affix dropping would not explain the distribution of negation in early English utterances. Harris and Wexler show that bare negatives in early English, that is, negative adverbs unsupported by an auxiliary, only occur with uninflected verbs as in (4a) and never with inflected forms as in (4b). (@ indicates that the form or utterance is unattested in the acquisition data.) As Harris and Wexler note, this asymmetry is unexpected if the bare form results simply from the dropping of finite morphology.2 (4) a. Mommy not go. b. @Mommy not goes. 1
An exception are the verbs have and be, but as we will see later, auxiliary verbs never occur as RIs. Children use both doesn't and don't with third person singular subjects in negative utterances, where the latter type of utterance could be considered an agreement error. We assume that do is inserted here to support n 't. It is interesting to note that when inverted, auxiliary do is always correctly inflected. 2
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Despite the theoretical appeal of Wexler's conjecture, we will show that it is too general. As we will see, there are both quantitative and qualitative differences in the behavior of the English bare form and the root infinitive in the other languages studied. We will further show that these differences stem precisely from the morphosyntactic difference between true infinitives and the English bare form, which is not in fact an infinitive. 2.2. The grammatical representation offiniteness and RIs Now that we have concluded that RIs constitute a construction type in its own right, different from finite constructions, we turn to the question of their grammatical representation. Various approaches are available in the literature. One such approach, championed by Radford (1990) and others, holds that the Rl-phenomenon results from the absence of functional categories. The idea is that functional categories are subject to maturation, and that early grammars consist solely of lexical projections (cf. also Lebeaux, 1988). Since the Infl-projection, or whatever inflectional projections comprise the label Infl, is a functional category, the absence of -s in the examples in (3) is an automatic consequence of this maturational theory. It should be noted that this explanation is strongly inspired by the bare form phenomenon in English, the only language considered by Radford and most other proponents of this theory. The presence of an infinitival marker in the Rl-utterances in (1) is less evidently in congruence with the idea that early grammars have only lexical projections. Moreover, the fact that the Rl-construction occurs alongside finite clauses and shows different properties argues strongly against this maturational account. Another approach is Rizzi's (1994) theory of truncation, according to which RIs result from truncating part of the top structure of full clauses. On this approach the child's grammar has in principle the full clausal structure available. The Full Clause Hypothesis also underlies various analyses which postulate the underspecification of particular functional categories in the top structure of the clause. This has been the tack that we have taken (cf. Hoekstra and Hyams, 1995, 1996, 1997). Our underspecification analysis, the details of which we outline below, is part of a more general theory of the relationship between two aspects of language, the morphosyntax and the interface (or discourse) conditions which govern the expression of morphosyntax. We propose that children converge on the morphosyntax of their ambient language very quickly, as is evidenced by the kind of properties we reviewed above concerning agreement and form-position correlations, but that children are less restricted than adults in the grammatical options allowed by the relationship between grammar and discourse. In particular, we take the position that finite and non-finite constructions are grammatical in the adult system as in the child's system, but that the Rl-construction is much more limited in the adult output because of a bleeding relationship that exists between RIs and finite utterances. We shall return to this difference between adult and child systems in Section 5. Let us now briefly sketch the representational system that we envision. Our basic assumption with respect to finite clauses is that they are grammatically anchored. By this we mean that the temporal location of the eventuality denoted by
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the VP is fixed through a temporal operator, which we assume is located in C, following Enq (1987) and Gueron and Hoekstra (1989). The notion of finiteness refers to this fixation, as finiteness makes visible a chain between the operator and the verb, or, more specifically, the Tense position. Tense itself is taken to be a pronominal, which receives the status of pronominal variable if it is connected to a tense operator (TO) through a visible tense-chain. This is depicted in (5): (5) TOjF!... F n ... Tensej VP Languages vary with respect to the morphological extensions that are used to make the tense-chain visible. This is to say that the notion of finiteness is expressed in different ways in different languages. Some languages give overt manifestation of finiteness in terms of a tense-morpheme, for example, Japanese. Others express finiteness with person morphology, and yet others through number morphology. So, in Dutch, a present tense finite verb is morphologically marked for singular or plural, but not for either person or tense. It is therefore number morphology in Dutch that makes a tense-chain visible in the case of present tense.3 A language such as Japanese makes a tense-chain visible through the morphological expression of tense, and languages such as Italian, Spanish and Catalan make the chain visible through the expression of (at least) person morphology. We furthermore observe that not all child languages allow RIs. The empirical generalization in this respect is that RIs occur only in languages where the expression of finiteness may be done exclusively through number morphology. Languages where finiteness is always expressed with person agreement, or with tense-morphemes appear not to allow RIs. This can be seen in Table 4. In this table we divide the languages in non-RI languages, where the phenomenon occurs sporadically at best, and Rl-languages, where it occurs with much higher frequencies (with some amount of variation depending on the child and on the language). It is worth noting that English has the highest frequency of non-finite forms, ranging from 75% to 81%. We will return to this point below (in Section 4) when we discuss the differences between English and the other Rl-languages. In order to capture this empirical generalization, Hoekstra and Hyams (1995) propose that the Rl-phenomenon results from the optional underspecification of the functional head Number. If Number is unspecified in languages where only number morphology expresses finiteness, e.g. Dutch, no tense-chain is made visible and the verb is non-finite. In this instance, Tense is not bound as a pronominal variable by a tense operator, but rather has the status of a free pronoun, which gets its interpretation discursively. In that case, the structure is unanchored. In person-marking and 3
We take the -t suffix to be an extension of singular number. Its absence in first person follows from the assumption that first person is unmarked (cf. Kayne, 1989). We similarly follow Kayne in assuming that English -s expresses singular number, the absence of -s in first person following from the same assumption, and its absence in the case of you following from the assumption that you is grammatically plural, like French vous. The inclusion of German and French among the Rl-languages may be surprising in view of the fact that these languages apparently have person marking morphology. See Hoekstra and Hyams (1995) for motivation and discussion of this point.
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Table 4 Frequencies of root infinitives in child language (partially based on Sano and Hyams, 1994) Non-Rl languages Child
Age
Italian (Guasti, 1994)
2 ;0 1;ii 2 ;1 2 ;0-2 ;5
Diana Martina
%RIs
0.00 0.16 0.04 0.07 Italian Paola ;7-2 ;6 0.08 (Schaeffer, 1990) Daniele Massimo ;7-2 ;6 0.06 ;7-2 ;6 0.07 Gabriele ;7-2 ;6 0.05 Orietta •1-2 ;5 0.10 Elisabeta ;9-2;5 0.05 Francesco Damariz 2 •6-2 ;8 0.05 Spanish (Grinstead, 1994) Juan 1 ;7-2;0 0.12 2 ;i-2 ;4 0.10 1;11-2;6 0.03 Guillem Catalan (Torrens, 1992) 2 ;0-2 ;5 0.03 Marti 2 ;3-2;8 0.02 Toshi Japanese 2 ;8-2 ;10 0.08 Ken (Sano, 1995) Masanori 2 ;4 0.10
RI languages French (Pierce, 1992)
Child
Nathalie Philippe Daniel
