Rationality and Scientific Discovery Stephen Toulmin PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association, Vol. 1972. (1972), pp. 387-406. Stable URL: http://links.jstor.org/sici?sici=0270-8647%281972%291972%3C387%3ARASD%3E2.0.CO%3B2-Q PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association is currently published by The University of Chicago Press.
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STEPHEN TOULMIN
RATIONALITY A N D SCIENTIFIC DISCOVERY
INTRODUCTION
Philosophers of Science have long paid lip service to the desirability of distinguishing the questions that arise about the propositions (statements, hypotheses) of a science from those that arise about its concepts (terms, ideas); but hitherto there has been a curious hesitation on their part to explore the consequences of this distinction as far as they will take us. This hesitation is understandable in those writers whose primary commitment is to the methods of mathematical logic, with its formal analysis of propositional systems and relations. But it extends also to those who have no such commitment: e.g. the pragmatists. (Recall William James's confused question, "What makes an idea true?" - as though concepts could be true-or-false, in the way propositions are!) The account of scientific change and rationality outlined in this paper, and set out at length in my recent book on Human Understanding, is designed to show how a full understanding of those consequences can help us to move beyond current quandaries in the subject to a more constructive set of philosophical, historical and sociological questions. A few introductory remarks may help to put this enterprise into a clearer context. To begin with, then: let us notice briefly certain contrasts between the philosophical traditions that sprang, originally, from the empiricism of Ernst Mach and the neo-Kantianism of Heinrich Hertz, respectively. On the one hand, Mach has been the single most dominant influence on the philosophy of science in the first half of the 20th century. At least since 1920, the most influential approaches to the subject have all been 'empiricist' in method, and directed towards problems about scientific propositions. All questions about the 'validity' of natural science have been translated, as a result, into questions about how we verify / confirm / corroborate / probabilify / falsify / support and/or refute scientific theories, hypotheses, conjectures etc. And these questions have been taken to refer, primarily, to propositions in which the technical terms Kenneth F. Schaffner and Robert S. Cohen (eds.), PSA 1972, 3 8 7 4 0 6 . AN Rights Reserved Copyright 0 1974 by D. Reidel Publishing Company, Dordrecht-Holland
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(ideas, concepts) of the science concerned figure directly as subjects or predicates: propositions about (say) energy, rather than about the concept 'energy'. The hope has then been that we might succeed in explicating the rationality of scientific beliefs, and notably of changes in scientific belief, by reference to the logicality of the formal connections linking alternative hypothetical propositions in scientific theory to the evidence supporting them. Yet this hope has become confused and tenuous wherever the transitions of the discussion involved major innovations in the concepts of the relevant theories. For hypotheses stated in terms of theories constructed around quite different concepts will have no subjects or predicates in common; and how, in that case, are we to investigate the formal connections between them? How, indeed, are we even to investigate their formal connections to a common body of evidence? Hence the vexing problem of 'incommensurability', as found in the arguments of Kuhn, Feyerabend and others; and hence the attractions of the view that such transitions are inevitably radical or revolutionary, and involve some sort of 'rational discontinuities'. On the other hand, we may contrast a parallel tradition in philosophy of science which might be called 'transcendentalist', since its final inspiration is the arguments of Kant. Hertz is the modem exemplar of this approach, but we may include also such subsequent writers as Wittgenstein (an admirer of Hertz), W. H. Watson and Friedrich Waismann. This approach differs from the empiricist approach in two main respects: in the priority it allots to concepts, as opposed to propositions, and in the account it gives of the empirical basis of scientific theories. The present paper is an attempt to pursue this approach one stage further. In the first place, then, the transcendentalist philosopher of science treats questions about the concepts in terms which the theories of a science are framed as more basic than questions about the theoretical propositions that can be stated in those terms. Without prior concepts and/or explanatory procedures, there will be no such propositions. The fact that we do (or do not) regard a particular set of concepts and procedures as 'adequate' decides, not what theoretical questions are trueor-false, but what theoretical questions even make sense. So, in framing acceptable scientific explanations, we bring to bear some currently authoritative set of concepts and explanatory procedures to interpret
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the events, processes and/or phenomena concerned, and that background of concepts and procedures is presupposed if the resulting theoretical propositions are to have a sense at all. In the second place, the transcendentalist philosopher gives quite a different account of the empirical burden (content and reference) of science from the empiricist. This empirical basis is specified, not by listing 'true' (well-supported, corroborated) propositions stated directly in terms of the theory, but rather by indicating over what range of cases, on what conditions, and with what degree of exactitude, the theory in question can be used - i.e., has been found to fit - in accounting for the relevant events, processes and phenomena. (Consider again, e.g. the passage about Newtonian mechanics in Wittgenstein's Tractatus, Paragraphs 6.342ff: also, the family of statements such as, 'Snell's straightforward treatment of refraction breaks down in the case of anisotropic media like Iceland Spar'.) The subjects and predicates of genuinely empirical reports in science, on this view, are not such things as energy and refraction, but rather the concept 'energy', Snell's analysis of 'refraction', etc. In this sense, the genuinely empirical propositions of a natural science may be spoken of as 'meta-statements'. Correspondingly, the theoretical problems that face scientists in phases of serious conceptual innovation commonly require to be specified in the form of 'meta-questions', i.e, as questions about the scope, adequacy, accuracy etc. of the relevant theory, rather than' as questions stated in terms drawn from the theory. (For instance: 'Can we find some way of extending Snell's treatment of refraction to cover the anomalous behavior of anisotropic media?') Theoretical problems and solutions are, thus, essentially concerned with how scientific concepts and explanatory procedures can be applied so as to yield satisfactory explanations, not with the verification or falsification of statements in which the corresponding theoretical terms figure directly as subjects or predicates. From this alternative (transcendentalist) point of view, accordingly, the crucial philosophical questions about theoretical innovation and discovery in science are concerned, not with any direct logical connections between theoretical hypotheses and supporting evidential reports, but with the comparative adequacy of the explanatory treatments associated with one or another set of theoretical concepts and procedures; and, in particular, with the dual process of variation and critical selection
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to which those concepts and procedures are exposed. And these questions will, inevitably, need to be dealt with in terms of a functional rather than a formal analysis: i.e. by comparing the practical effects of employing the explanatory treatments embodied in the currently accepted theories, on the one hand, and in one or another variant, on the other. From this point of view, furthermore, the problem of 'incommensurability' is no longer a problem. Of course, theoretical propositions stated in terms of rival theories will frequently have no subjects or predicates in common. But nothing radical follows from this fact about their comparability. For what needs to be compared, in that case, is something which can be specified only in meta-statements: viz. the overall scope, exactitude, adequacy etc. of the explanatory treatments available to us, if we make use of one or the other theory. What follows is a digest of the positions presented in Human Understanding, Part I , Chapters 2-4 and 8. 1.1. The basic process of scientific change has been described as 'criticism and the growth of knowledge'. Rather, it should be characterized as 'criticism and the improvement of understanding'. 1.11. The phrase 'growth of knowledge' implies an accumulation of propositions claimed as 'known', and organized theoretically - at most in logically articulated patterns, for the sake of 'intellectual economy' (Mach). All serious scientific innovation, by contrast, aims at explanation of a kind that goes beyond a logical reorganization of given 'facts', and reinterprets our experience in terms of fresh concepts, methods of representation and explanatory procedures. 1.12. So much for the 'covering-law' model of explanation in science. If it were a serious scientific problem to account for the fact that some one raven was black, then it would a fortiori be a more serious problem to account for the fact that all ravens are black. Far from being an explanans, this generalization would be even more of an explanancium. ('What? All ravens are black? Now, that really does take some explaining! What then - we must ask - are the mechanisms of pigment-formation in avian plumage? And what advantage could such coloration have
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provided to the evolutionary precursors of ravens?' But all such explanatory questions involve new types of concept, and so reinterpret not merely entail - the phenomena.) 1.2. Questions about scientific concepts underlie (are 'logically prior to') questions about scientific propositions. How we view any aspect of nature or 'domain', as scientists - in what terms (using what 'concepts') we frame our problems about it - decides what questions we shall ask about it, and so predetermines what propositions we can put forward at all for verification/falsification/corroboration/confiation or whatever. (Recall Kant on 'putting Nature to the question' ...but it is always our question !) 1.21. The example of Frege has encouraged philosophers to believe that 'concepts' must be analyzed always in the context of the propositions and 'propositional systems' in which they figure; and it his recently been taken for granted that this holds for the concepts of natural science exactly as it does for those of, say, arithmetic. Perhaps a case (if not a cast-iron one) can be made out for distinguishing absolutely, as Frege himself does, between our historically and psychologically changing 'number-conceptions' or 'number-words', and the 'pure arithmetical concepts' that become apparent to 'the eye of the mind' when all historicopsychological 'accretions' have been 'stripped away'; but it is highly questionable whether the same move is open to us in other fields. (Kant thought Newton's mechanical concepts were 'pure', in Frege's sense; but in so doing he only prejudged the question against a future Einstein!) 1.22. The alternative phrase 'improvement of understanding' thus has the merit of redirecting our attention, away from the accumulation of 'true' propositions and propositional systems, and towards the development of progressively more 'powerful' concepts and explanatory procedures.
1.3. The philosophical invitation to analyze the intellectual content of our positive knowledge ('the structure of science') exclusively in the form of 'propositional systems' risks two further confusions, which call for comment here. Firstly: within pure mathematics, the goal of
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'systematization' (including 'axiomatization') is intrinsic to the very enterprise - by axiomatizing, Hilbert was ipso facto doing 'better' mathematics. In a natural science, on the other hand, the extent to which we 'systematize' our theories needs to be justified by its extrinsic contribution to the current explanatory goals of that science - cf. the Introduction to Hertz's Principles of Mechanics. 1.31. Secondly: while it may often be possible to represent the intellectual content of a single theory within a natural science as a coherent 'propositional system', this is not typically the case for an entire natural science. Pushing the point to paradox, we might say that the English translation of Mach's Die Mechanik, viz. The Science of Mechanics, is mis-named. Mechanics is not a Science: rather, it is a theoretical branch of (a mathematical system put to use in the service of) the Science of Physics. Note that nowadays mechanics is commonly expounded in scientific texts in a preliminary section, under the title 'mathematical methods for physicists', before any genuine phenomena come under discussion. 1.32. True: to the extent that several different concepts (e.g., Newton's force, mass and quantity of motion) are introduced into the content of a science together at the same time, for a single explanatory purpose, there may well be 'systematic logical relations' between them - simply because they are interdefined. To that extent, the intellectual content of a science may well include certain 'families' of concepts, and these can be seen as 'pockets' of logical systematicity within the larger, less systematic content. In general, however, the concepts comprised in the intellectual content of an entire science are not so related. So we can afford to view this content, not as a 'conceptual system' (still less, as a 'propositional system') but rather as a 'population' of concepts and explanatory procedures, having varied origins, functions, lifestories, etc. 1.4. This populational approach has one immediate advantage. A population is something intrinsically capable of historical development. Given such a point of view, conceptual change poses no mysteries: it is of the essence of science.
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1.41. By contrast : the familiar structural/systematic approach leads directly into difficulties over conceptual change. Any propositional system represents at best a 'time-slice', abstracted from the historicallydeveloping content of a natural science: as such, it presupposes the provisional adequacy of the relevant concepts, and displays a static set of 'synchronic' relationships between propositions framed in terms of them. In this way, as a direct consequence of our own abstraction, we make conceptual change extrinsic to the content of the science concerned. (Cf. Aristotle on points and lines: We cannot re-construct a continuous line - or an historically-changing science - simply by accumulating enough of the points - or successive propositional systems that we have ourselves generated by abstraction from it !) 1.42. Notice : this difficulty arises not just for those who see the structure and development of ideas as linked in propositional systems, but also for R. G. Collingwood, whose systems are entire 'constellations of absolute presuppositions', and for T. S. Kuhn, whose complete 'paradigms' are all-embracing, and shape the content of a whole science. It does not arise, by contrast, for those who used the term 'paradigm' in its classic sense, as introduced by G. C. Lichtenberg in the late 18th century, picked up and extended by Ludwig Wittgenstein, and applied in philosophy of science by e.g., W. H. Watson and N. R. Hanson. The acceptance of a multiplicity of explanatory 'paradigms' in a science allows for radical changes and reinterpretations at any level, without the need to invoke 'revolutionary' discontinuities. (Cf. the sociological illusion that an entire 'society' forms a 'system', which likewise lends color - by reaction - to the anarchist view that 'social change can be radical only if it is revolutionary'.) 2.1. The primary unit of constancy and change in the diachronic development of science is the 'discipline'; and the domain of any discipline is characterized by a set ofproblems, which arise from the existence within it of particular (though provisional) ideals of explanation. Consider, e.g., the question, 'What would it be like for our explanation of the physical properties of matter to be exhaustive?' A classical 19th century scientist would give quite a different answer to this question from a 20th century quantum physicist. Such ideals are thus not fixed
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or formal, but substantive and liable to historical change. They serve, so to say, as the current horizons of intellectual ambition within the sciences concerned. (Compare the answers to the above question implicit in the work of Newton, Dalton, Maxwell, J. J. Thomson, Heisenberg, and Feynman.)
2.1 1. The current reservoir of problems in a discipline is determined by the gap, or shortfall, between the current explanatory capacities of the presently established concepts and procedures, and those that would ostensibly be required in order to fulfill the recognized ideals. The scientist 'makes better sense' of his domain when he narrows this gap, between what he can at present account for, and what he can legitimately ('reasonably' or 'in principle') hope to account for, in the long enough run. 2.12. The basic problems of a scientific discipline are thus 'conceptual' problems, in a sense which marks them off from problems of two other kinds : formal/mathematical problems, and straightforwardly empirical problems. Formal/mathematical problems take the form, 'Given that the concepts c,, c,, ..., are adequate to our explanatory needs, how can we better organize the theories and arguments in which they figure?': straightforwardly empirical problems take the form, 'Given that the concepts c, , c,, ..., are adequate to our explanatory needs, what is the observed truth about subject-matter x, y, ..., in respect of these concepts?' By contrast : authentically 'conceptual' problems take - precisely the form, 'Given that the concepts c,, c,, ..., are in some respect inadequate to the explanatory needs of this discipline, how can we modify/ extend/restrict/qualify them, so as to give us the means of asking more fruitful empirical or mathematical questions in this domain?' (It is in this sense that conceptual problems are necessarily 'meta-problems', posed about concepts, rather than directly using them.) 2.2. Given that any live natural science comprises always a reservoir of outstanding problems, its intellectual content will comprise - correspondingly - not only a body of 'established' concepts and procedures, but in addition a pool of conceptual variants. These variants are referred to by scientists as 'possibilities' - not just in a Humean sense, as being
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propositions formally consistent with the empirical data, but in a stronger sense. The question, 'Is this proposed theoretical conceptual change a genuine possibility?', means in practice, 'Does this proposed change hold out enough prior promise of solving outstanding problems in the discipline to warrant a place on the current research agenda of the science?' (Cf. Shapere, on the kinds of reasoning that go on around that preliminary question, long before any novel explanations or justificatory arguments are arrived at that lend themselves to orthodox philosophical criticism within the empiricists' 'context of justification'.) 2.21. In the process of conceptual variation, concepts belonging to a single, interdefined family will commonly vary together: e.g., if we modify the concept 'mass', questions will inescapably arise about 'force' and 'momentum' also. These families apart, the co-existing concepts and procedures of a science, and the accepted relations between them, are free to vary independently. (The life-history of the concept 'atomic number' 'which began as the index number in a list, and was transformed into the size of a nuclear charge, indicates how quite a minor change in these inter-relations can dramatically alter the status and implications of a scientific concept.)
2.2. The pool of acknowledged conceptual variants provides the raw material for conceptual change in science. Significant historical questions can then be posed, having to do with the factors and/or considerations affecting the rate and/or direction of conceptual change, in this-or-that science, within one-or-another historico-cultural milieu. (On this, see Section 4.2 below.) 2.3. The primary locus of intellectual choice ('rational judgment') within a historically-developing scientific discipline is thus the question, 'Which if any of the current pool of conceptual variants has what it takes, in order to solve a sufficient range of the outstanding conceptual problems in - and so make a significant difference to the explanatory power of - the relevant discipline? Which of these variants (in other words) will bring the actual explanatory procedures of the disciplines significantly nearer to its current explanatory ideals, and so warrant incorporation into the body of established concepts in that discipline?'
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2.31. As to this question, no universal formula or decision-procedure can be given. (The particular changes that are 'significant' in any specific context are something the apprentice scientist learns in the course of his apprenticeship.) Concepts can be modified in at least three distinct kinds of respect: (a) as to terminology, (b) as to the forms of their associated explanatory procedures and methods of representation, and (c) as to the scope and manner of their empirical application. Furthermore, the consequent increases in explanatory power can be of at least five distinct kinds: e.g., accounting for fresh phenomena/accounting more exactly for existing phenomenalintegrating hitherto-separate theories within a single discipline/demolishing boundaries between hitherto-independent disciplines/reconciling concepts within a science with extra-scientific concepts, etc., etc. There are thus at least 15 distinct ways in which scientific concepts can be 'improved'. 2.4. Accordingly, even in clear cases - where there exists a sufficient consensus among the practitioners of a discipline about its current explanatory ideals, and so about the considerations bearing on choices between conceptual variants - the assessments of merit actually involved in the practice of science are both highly complex and substantive. 2.41. Firstly: such choices normally demand a balance of gains against losses, and so call for 'judgment'. The philosopher's ideal of a perfectly predictive, compact, coherent, elegant.. . science is a Utopian ideal. In practice, scientists have to decide how much ground they should give on one front, in return for an advance on another. (Copernicus' geometrical constructions of the planetary motions were, at first, less convenient and elegant than the accepted Ptolemaic ones; but they paid off in terms of intellectual consistency. Even so, his contemporaries were not unanimously agreed about whether this was a good intellectual bargain !) 2.42. Secondly: resort to general abstract terms, like 'predictive', 'simple' and the rest, does not eliminate this element of judgment. For these terms too have to be reinterpreted within each new phase of each fresh discipline. In general relativity, for instance, what is to count as 'simple'? Is the tensor calculus 'simpler' or 'more complex' than the
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familiar algebra of classical physics? Where the theories and phenomena of different disciplines are framed in such diverse terms, there appears no scope for universal, philosophical measures or indices of 'simplicity'. 3.1. When (i.e., on what conditions) is the consensus among practitioners about the current ideals of their discipline 'sufficient'? As to this question, consider Kekule on the 'ultimacy' of atoms and molecules, and Duhem on 19th century French and British electrical theory. Clearly, Duhem's stylistic objections to the ambitions of Maxwell and Lodge still left a predominant (even if not a 100%) measure of agreement over the current goals of electrical theory on the two sides of the Channel. 3.11. Evidently, consensus does not demand unanimity. Rather, a sufficient measure of agreement is required among those scientists whose authoritative standing in the profession is based on the range of their experience. (N.B. This does not mean '...on the diversity of their Empjindungen, or sense-experiences', in Mach's sense of the term. It means, rather, '...on the range of their professional experience, in seeing how the established concepts and explanatory procedures of the discipline can be put to use, in the business of 'making sense' - i.e. yielding a Bild or Darstellung in Hertz's sense - of the relevant aspects of Nature'.) 3.12. In this respect, we can take note of the manner in which different 'generations' of authoritative scientists co-exist, within a single discipline and/or profession, as its intellectual horizon shifts. (Recall Rutherford's remarks, in old age, about his not even understanding the theoretical goals of his pupils' pupils.) Each generation of influential scientists, we might say, refashions the picture of Nature for itself, using the ideals of its predecessors and older contemporaries as no more than a startingpoint. 3.2. To speak of some group of scientists working within a given discipline as having an 'authoritative' position, either as individuals or collectively, is not to make apurely sociological statement about them. It is not just to report, but to endorse, their claim to 'authority'. Insofar as these men claim to speak in the name of the discipline in question,
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correspondingly, their judgments are always open to criticism, and in normal (or 'clear') cases this criticism can be pressed home at the time. 3.21. Thus: the question in such clear cases is, quite simply, whether the conceptual innovations accepted (or dismissed) by these authoritative figures do (or do not) have the capacity to narrow the gap between the actual capacities of the established explanatory procedures of a discipline and the explanatory ideals currently accepted within it. Occasions may arise, in these terms, for challenging the judgments of even the most authoritative scientists or scientific organizations as 'too hasty' or 'too conservative'. (Here, generational effects are again significant. The Royal Society of London took until 1961 to recognize molecular biology officially as a serious subject of research.) 3.3. For philosophical purposes, however, the most significant questions arise, not over normal or 'clear' cases, but rather over 'cloudy' ones. Consider the phases of 'strategic uncertainty', during which no sufficient measure of consensus exists within a discipline - at any rate, for the time being - about its current ideals of explanation. During these phases, there can be no codified set of considerations and/or procedures for debating, certifying and/or validating conceptual variants, or innovations in explanatory procedure. The heart of the theoretical argument now becomes, instead, what the explanatory goals of the discipline should now become; and, what the considerations relevant to conceptual choice should accordingly be for the future. 3.31. Consider three examples: (a) the exchange between Mach and Planck in 1910-191 1 over the proper new intellectual strategy for 20th century theoretical physics; (b) the manner in which Delbriick, around 1950, justified the move on from classical biochemistry to molecular biology; and (c) the continuing dispute over the ultimate adequacy of particle physics. During such phases of strategic uncertainty, or 'cloudiness', we can no longer draw any clean and absolute line between the question, 'By what criteria is this judgment made?', and the question, 'Who judges?' Rather, we shall have to ask, 'By whose criteria.. .?' Planck's or Mach's, Avery's or Delbriick's? Compare what we do in constitutional law where, in an intrinsically 'cloudy' case, Frankfurter's
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opinion may point the law in a new direction, different from that which a Holmes or a Warren would choose. 3.32. Although the arguments that arise in such 'cloudy' cases are not formal or rule-governed, they are none-the-less full of 'reasons', and open to critical examination. In this respect, they resemble commonlaw arguments - as involving appeals to precedent - rather than codelaw arguments, in which some formal procedure is available for settling the issue. Consider, e.g., the argument between the Copenhagen quantum theorists and their critics, reported in the symposium, Observation and Interpretation. This dispute began as an abortive appeal to 'authoritative, established procedures', in a context in which no common body of agreed procedures was available, but later moved on to a trading-off of historical precedents or object-lessons: e.g. 'Don't make the mistake William Prout made, in trying to go far beyond Dalton's atomic theory as early as 1815' and 'Don't forget how Pierre Duhem made a fool of himself, by rejecting J. J. Thomson's ideas about sub-atomic structure'. In the nature of the case, no alternative was left to this kind of 'historicocritical' analysis. 3.33. For there to be a phase of strategic uncertainty in a science, it is in no way necessary that there should previously have been a 'crisis', in Kuhn's sense of the term. New intellectual horizons may open up in a science for half-a-dozen kinds of reasons - exhaustion of the previous domain of problems, ingenuity of imagination, etc. - of which gross intellectual inconsistencies (or similar 'crisis phenomena') are only one. 3.4. In saying that we can, at such times, do no more than opt between (say) Planck's strategy and Mach's strategy - as between Frankfurter's opinion and Warren's opinion - we are not introducing any element of subjectivity into the progress of science. On the contrary: strategic redirections, and the judgments of the scientific 'Supreme Court Justices' who propound them, are as subject to external objective constraints as anything else in science. 3.41. The difference is this: the experience by which the soundness or unsoundness of any proposed new strategy must be decided lies essentially
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in the future rather than the present or past. The question is now: 'Which of the proposed new strategies (and the associated intellectual ideals) will turn out to suggest the more illuminating new concepts and explanatory procedures - i.e. ones that will in turn prove to yield propositions which lend themselves to extensive and exact new comparisons with our actual experience of Nature?' 3.42. This question - though without doubt an 'objective' question about the actual course of experience, not one about 'subjective' intellectual preferences - can be dealt with at the time of asking only on the basis of a 'rational bet'. Fifty years later, we may be able to look back and say, 'Mach's strategy paid off in the short term, by generating the quantum-mechanical doctrine of observables, yet since 1950 the pendulum seems to have been swinging in the direction of a more Planckian style of theory'. Yet none of this could, of course, have been said in 1911. 4.1. This philosophical shift in our interpretation of science - from 'fuller knowledge through more true propositions' to 'deeper understanding through more adequate concepts' - has a number of irnplications for the historiography of science also. 4.1 1. To begin with : we may now reconsider the assumption that the 'objectivity' of scientific knowledge makes it possible for us (indeed, requires us) to distinguish absolutely between disciplinary or factual questions, of the form ' What is known/established/explained ... ?', and professional or personal questions, of the form 'By whom (or to whose satisfaction) are these matters known, established etc.. ..?' If we could regard the work of science as concerned merely with checking off the correctness of propositions (or systems of propositions) against external objective facts, the history of the resulting scientific disciplines could then be written quite independently of the history of the corresponding scientific professions, and the biographies of the individual scientists involved. From the present point of view, however, that is no longer the whole story: the concepts in terms of which scientific propositions are framed obtain their 'objectivity' in another way from the propositions themselves.
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4.12. Once we accept the scientist's responsibility for framing his own concepts and questions, the absolute distinction between intellectual (disciplinary) and sociological (professional) issues becomes no more than a first approximation. During phases of strategic consensus we may still be able, for the time being, to separate the intellectual development of a discipline itself - the affiliations and applications of its ideas, and the reasons for changes in them - from the history of its human aspects - the individuals and organizations responsible for 'carrying' those ideas, and the causal influences acting upon them; but this can be done only at a price. For this separation has the effect of concealing from view the continuing 'generational' changes in the aims and strategies of any science; and this makes the occasional, more radical redirections in aim and method appear needlessly mysterious, discontinuous and 'revolutionary'. Delbriick's new program for biochemistry, Maxwell's novel treatment of electromagnetics, and the rest, had clear (objective) merits while remaining in other respects essentially personal productions.
Again: historians have often handled those scientific changes that are explicable in terms 'internal' to a discipline separately from those that are influenced by 'external' factors or causes. Yet there has been a fair amount of confusion about the relations between the two resulting types of history. Thus, it has been customary to treat the disciplinary question, whether some new hypothesis is or is not confirmed by a particular experiment, as a purely 'internal' matter - one step in the sequence of steps that constitutes the rational life-history of the discipline in question - while the social or professional question, why there was (or was not) active support for, e.g., astronomy in a particular milieu, has been treated by contrast as a purely 'external' matter - the effect of sociological, economic, or even religious causes. 4.2.
When we consider the development of science as a conceptual evolution, we are compelled to soften the absoluteness of this distinction also. At one extreme, for instance, the rate and direction of conceptual variation in a discipline may largely be the product of external factors (institutions, occasions, patronage, ideological interest, etc.); but it depends also, in part, on internal considerations (the problematic 'ripeness' of the current fields of study, their intrinsic significance for 4.21.
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the discipline in question, etc.) At the other extreme, the selectionprocedures to which conceptual variants are exposed may largely be an internal matter, determined by the character of the accepted goals and strategies of the science concerned; but the very nature of those goals must now be viewed also in its broader context, and this in turn involves us in paying attention to external factors also. 4.3. We can thus now redescribe the relationship between 'reasons' and 'causes' in the historical development of a science. In a phrase: a purely 'causal' history is at each point retrospective, diagnostic, genealogical, while a purely 'rational' history is at each point prospective, justificatory, judgmental. 4.31. For example: the question, 'How did Ptolemy's Almagest come to be displaced by Copernicus' De Revolutionibus?', can be taken in either of two ways. It can be construed as meaning, 'What succession of temporal processes and influences (causes) brought about this displacement as their effect?'; or it can be construed as meaning, 'What sequence of intellectual investigations and achievements (reasons) warranted this displacement as their outcome?' 4.32. These two interpretations are complementary, not conflicting. The fact that Johannes Kepler recognized the force of Copernicus' arguments - i.e., accepted them as 'good reasons' - was itself a historical 'cause' operative in the ancestry of 17th century astronomy; while the historical fact that such-and-such an event - e.g., Lavoisier's mercury experiment - had such-and-such an outcome can serve, in turn, as a 'reason' for changing our ideas about calcification. Either way, however, the shift from 'reasons' to 'causes' or vice versa rests on an interpretation. (Arguments provide reasons not causes; but the fact that those arguments carry conviction can be a cause, etc., etc.) 4.33. There is a similar relationship, in the theory of organic evolution, between a genealogical account of the ancestral lineage of some organic form ('From what succession of precursors has this species descended?') and an ecological account of the tests or demands to which those ancestral precursors were successively exposed ('By what sequence of
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adaptions did the species acquire its present form?'). In this sense, the 'rational' history of a scientific discipline is concerned - quite exactly with questions of intellectual ecology. 4.4. But (some will want to ask) can we not at least abstract certain general and universal criteria of scientific merit from the diversity of historical contexts, and so create a secure base, or forum, from which we can pass philosophical judgment on scientific changes 'from outside' the chances of the historical process? 4.41. This could be done effectively only if it were possible to apply such highly abstract criteria of conceptual choice to all actual cases in an unequivocal manner, in the form of a completely general 'theory of confirmation' - or, rather, a completely general 'theory of conceptual adequacy' - capable of yielding a clear basis for agreement in all situations. 4.42. But it now appears that this is not a realistic goal. Even if we continued to operate with such vague terms as 'simplicity', and 'predictiveness', we should find that they had to be recontrued afresh in each new type of context, in the light of the current disciplinary ideals of explanation - 'What counts as a 'prediction' from the standpoint of, say, contemporary molecular biochemistry? As a result, the formal universality of the criteria will be purchased only at the price of indeterminacy. In general, indeed, the substantive considerations that serve as effective grounds of rational criticism, within the historically-changing loci of scientifiq judgment, have a relevance and binding-force whose sources can be recognized only from within the specific loci concerned. 5.1. The distinctive consequences of analyzing scientific change in terms of concepts and conceptual innovation, rather than of proposi,tions and propositional systems, can be indicated by restating certain of Karl Popper's familiar propositional theses in alternative conceptual terms.
5.11. Instead of regarding the fundamental issues for a science as consisting in the logical coherence of its propositional systems, and the
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falsifiability (or provisional corroborability) of its particular propositions, we now focus rather on questions about the explanatory adequacy of new concepts or methods of representation, and the fruitfulness of novel intellectual strategies. The 'adequacy' of new concepts is no doubt demonstrated inter alia by the fresh 'empirical truths' they yield; but it resides primarily in their constructive capacity to 'make better sense of empirical material already known. 5.12. The final destination of a natural science in this case becomes not so much a 'fully corroborated/confirmed/verified' system of propositions and propositional arguments as a 'fully adequate' population of concepts and explanatory procedures. (Let us, incidentally, rewrite William James' ill-phrased question, 'What makes an idea true?', in the form, 'What makes a concept adequate-to-the-current-problems/acceptablelworthy of incorporation into the current body of the relevant science?') 5.2. Popper's appealing formula, 'Conjectures and Refutations', is likewise unduly propositional. (Conjectures are hypothetical propositions, refutations are demonstrations of their falsity.) By contrast, conceptual variants are put forward, at most, in hypothetical 'metapropositions' - e.g. 'Perhaps the anomalous optical properties of Iceland Spar can be explained by introducing a novel, extended concept of double refraction'. Similarly, variants are selectively perpetuated, or rejected, not as a result of our 'verifying' or 'falsifying' them, but as a result of our seeing whether or no their adoption yields a significant improvement in the explanatory power of the relevant science. 5.21. If we reinterpret the content of science in conceptual terms, accordingly, we can replace Popper's formula by the explicitly evolutionary formula, 'conceptual variation and selective perpetuation'.
5.3. Popper's 'fallibilism' with regard to the propositions of science also has its conceptual counterpart. For the intellectual content of our sciences (their basic concepts, methods of representation and explanatory procedures) is always open to challenge, reconsideration and modification, even down to the most profound level: viz, that of intellectual aims and strategies.
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5.31. In course of time (we may guess) current ideas about the explanatory goals at which the major disciplines of science should be aiming will be reformulated yet again, as they have been in the past. With these further changes, there will come also changes in the criteria for appraising proposed conceptual variants; with them, changes in the actual bodies of established scientific concepts and explantory procedures; and, with these in turn, changes in the sets of propositions which it is 'open' - i.e. meaningful in that scientific context - to consider as either true or false. Yet we can no more anticipate such strategic changes than Bach could write Beethoven's Choral Symphony. At no point can we therefore demonstrate, as Kant hoped, that the basic rational forms of our scientific understanding are final and immutable. (Why should that worry us?) 5.4. 'What, then, makes the enterprise of natural science a rational one?' From Plato up to Descartes and Kant, philosopher-scientists took this question as an invitation to identify some system of propositions as being the uniquely authoritative one in the field concerned, which would therefore have the same claim on our intellectual loyalties in (say) physics that Euclid's system seemingly had in geometry. 5.41. Is this notion dead? What about the Unity of Science Movement? Perhaps we have only replaced Aristotle and Euclid by Frege, Russell and Peano, as architects of the definitively 'logical' or 'rational' system! 5.42. Yet there was always one odd thing about this philosophical program. Why should the 'rationality' or 'irrationality' of intellectual procedures require a final, immutable basis - so unlike that of (say) rational or irrational fears, attitudes and extra-scientific expectations? Surely, the rationality of science has less to do with the logical systematicity, or supposedly unique authority, of any one body of ideas or propositions than with the manner in which, and the considerations in the light of which, men are prepared to give up one body of scientific ideas or concepts in favor of another. 5.43. So understood, the branch of formal mathematics commonly known as 'rational mechanics' represents a Platonization of Newton's
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dynamics, which has the effect of removing Newton's basic dynamical ideas from the sphere of rational scientific criticism. What a misnomer! Meanwhile, the rational task of adapting our concepts to the fresh demands of our experience, so as to improve our scientific understanding, has neither a universal method nor a definitive end. Yet science is none the less rational for all that. What we must reconcile ourselves to as philosophers of science in theory, as working scientists do in practice, is the fact that we can develop effective scientific methods and worthwhile scientific ends only as we go along. 5.5. We can hope to understand only by 'doing what there is to be done' in the way of explanation; and what that is we shall have to discover for ourselves bit by bit, from our experience with alternative scientific strategies. So any natural science, however mathematical and sophisticated, remains empirical: based on the observed 'fact' that the current theoretical strategies have proved fruitful, to such-and-such an extent, in such-and-such types of problem-situations.
Committee on Social Thought, University of Chicago
