The Logic of Psychological Concepts

The Logic of Psychological Concepts Gustav Bergmann Philosophy of Science, Vol. 18, No. 2. (Apr., 1951), pp. 93-110. Stable URL: http://links.jstor.org/sici?sici=0031-8248%28195104%2918%3A2%3C93%3ATLOPC%3E2.0.CO%3B2-P Philosophy of Science is currently published by The University of Chicago Press.

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THE LOGIC OF PSYCHOLOGICAL CONCEPTS*t GUSTAV BERGMANN

The purpose of this paper is to provide a methodological rather than, strictly speaking, a philosophical discussion of its subject, the logic of concept formation in psychology. But even a treatment of this kind cannot entirely avoid matters of a more general nature, some of them logical, some epistemological. By insisting on the limitations of this essay I merely wish to caution the reader in three respects. First, those more general matters, logical and epistemological, will be kept at a minimum. Second, no attempt will be made to state them with the degree of precision and all the qualifications which are in order in a paper that addresses itself exclusively to logical analysts. Third, I shall for the most part content myself with stating them, without defending them in the way and in the sense in which a technical philosopher who speaks to his colleagues must defend what he asserts. The philosophical viewpoint here taken is that of Logical Positivism. But since Logical Positivism is a far-flung, complex, and still very active movement rather than a single school with a well-defined and, among its members, universally agreed-upon doctrine, the reader may fairly wonder to which of the several positivisms this acknowledgment refers. So it is, perhaps, neither useless nor improper to add that a statement of my philosophical position may be found in two articles in a recent handbook (1, 2 ) . 1. Concepts and Xtatements. If English were as neat a pattern as arithmetic or one of the schematic languages logicians have constructed, each word could be assigned to one of three categories. One of these, let us call it the first, would contain all structure words (synonym: logical words) such as 'and,' 'is,' 'all,' 'property.' Structure words do not designate anything in the sense in which the words in the other two categories do designate something. The second category would contain all proper names (synonym: particulars). In English and other natural languages we name for the most part only such things as people, mountains, rivers; for the rest we make shift with so-called descriptive phrases, com-

* Based on lectures delivered during the winter 1949/50 before the University of Minnesota chapter of Psi Chi and before the psychological seminar a t the University of Indiana. t By ignoring it I have, in this paper, implicitly taken a position on the counterfactuals issue which now raises so much dust. After this has been submitted, I explicitly discussed that matter in "Comments on Professor Hempel's 'The concept of cognitive significance'," t o be published among the papers presented a t the 1950 conference of the Institute for the unity of Science. See also Julius R. Weinberg, "Contrary-to-fact conditionals," J. Phil., 1951,48, 17-22. 93

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posed of words from the other two categories, such as 'the book on the table in front of you.' Into the third class we would put all concepts (synonyms: terms, universals), i.e., the names of all properties and relations, no matter how "simple" and "concrete" or how "complex" and "abstract." Thus, 'blue,' 'hot,' 'between' but also 'electric field,' 'habit,' 'psychopathic personality' are all instances of concepts. A definition of 'concept' as precise as one could make it would indeed have to use what I merely mentioned as an expository device, namely, a logician's schematization of natural language, e. g., that given in Russell and Whitehead's celebrated Principia Mathematica. But I trust that it is sufficiently clear what I mean by 'concept.' And, by the way, 1 did not mean to introduce 'simple9 'complex,' 'concrete' and 'abstract' as technical terms; I merely used them, loosely and vaguely, for the purpose of preliminary elucidation. While concepts are, schematically speaking, words, statements (synonyms : sentences, propositions) are strings of words. However, not every string of words is a statement. For instance, four proper names written doan one after the other do not make a statement. In natural languages like English the rules one must obey if one wishes to combine words into a statement are those of grammar; on closer examination they turn out to be a part of logic. But in this very informal paper I shall always use 'grammatically correct' instead of the corresponding phrase of logical theory. I t follows then that, literally, only grammatically correct statements are statements; however, it sometimes pays to emphasize this feature. For instance, I shall presently point out that a statement is conveniently called meaningful if and only if, first, it is grammatically correct and, second, one further condition, relating to the concepts that occur in it, is fulfilled. Only a statement, not a concept, can be either true or false. Obvious as this is, it is sometimes obscured by a tendency to use 'valid-invalid' or 'correctincorrect' as synonyms for 'true-false.' For if the need is felt t o divide concepts into sheep and goats, one uses again 'valid-invalid' or 'correct-incorrect.' Such ambiguity courts confusion. I t is, therefore, preferable to speak of concepts as either meaningful or meaningless. Yet, further reflection shows that in ordinary usage each of these two terms still covers two different meanings. 2. Two meanings of 'meaning.' In methodology an extreme illustration is often more effective than a long explanation. So I shall make use of this device. Consider, then, the following "biological" concept. A person's "B-coefficient" is obtained by dividing the sum of his weight (in pounds) and height (in inches) by his white blood count. Whenever we do not choose our terms with the particular care which in logical analysis is of the essence, we shall all say that the B-coefficient is meaningless. Nevertheless, it is meaningful in the obvious sense that a medical laboratory familiar with my definition can without difficulty ascertain a person's B-coefficient. This situation calls for a terminological agreement. I propose (1) to call the B-coefficient meaningful, and (2) to express the other idea involved in the ordinary usage by calling it a useless concept. The methodologist can only pronounce on meaningfulness in this limited sense; to decide whether a concept is, at a certain stage of our knowledge, use-

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ful is the scientist's business, not the methodologist's. A11 the latter can do is t o watch science at work and try to formulate, in a general way, the conditions under which a concept is considered useful (synonyms: interesting, fruitful). Assume, for instance, that somebody discovers a. significant correlation between n low B-coefficient and the incidence of cancer. Certainly, this would cause considerable raising of eyebrows; partly, a t least, because even if this "empirical" finding were well confirmed and the concept, therefore, unquestionably useful, we still would feel that we do not "understand". T o describe this unlikely but conceivable situation abstractly: First, a concept is useful if it occurs in a law of nature. Second, in a well-developed science we expect a newly discovered law to fit "theoretically" into the existing body of knowledge. I n fact, this is a large part of what we mean when we call a science well developed, and it is because of this feature that the story I made up sounds so unlikely. The analysis of concepts (and statements) that are (at the moment) useless scientifically is sometimes very useful if one wants to answer a methodological question or to clarify a philosophical puzzle. For instance, I shall presently maintain that in ascribing to another person conscious contents-in the literal sense in which Watson thought this could not be done--one makes a meaningful, though scientifically useless statement. If this is correct, then the behaviorist need no longer hide his embarrassment behind a superior smile when it is pointed out to him that outside his laboratory he shares the common-sense belief that the other fellow has, quite literally, a mind. This, by the way, is characteristic of the kind of help the philosopher can give to the scientist, particularly in a young science which, as it is the way of science, seems t o contradict common sense. 3. i'feaningful Concepts. Next, we must inquire under what conditions concepts and statements are meaningful or, as one also says, we must try t o formulate a meaning criterion. Now, if one were challenged to show cause why he considers the B-coefficient meaningful, he could say this: If you admit the concepts that occur in its definition (weight, height, white blood count) to be meaningful and if you admit that the definition is grammatically correct, then you must also admit that the B-coefficient itself is meaningful. This answer expresses in a specific instance one of the fundamental ideas of all empiricist philosophizing, from John Locke to contemporary positivism. This idea may, in three steps, be stated as follows. First, there is a class of concepts that refer to immediate19 observable characters (properties and relations), such as "blue,' 'hot,' 'between,' 'earlier.' These concepts are also called undefined, since what they refer to can only be learned by experience, not through linguistic explanation (definition). Second, any other concept C is meaningful if and only if1 there is a chain of grammatically correct definitions of the following kind: (a) the first contains, except for the concept it defines, only undefined concepts; (b) each contains, except for the concept it defines and for undefined concepts, only con-

* This does not, literally spealring, include the particle notions discussed in section 10. But there is no point in burdening the rest of the paper with the verbalism of a formulalion tllat includes then1

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eepts already defined in preceding members of the chain; (c) the last one is a definition of C. Third, a statement is meaningful if and only if it is grammatically correct and contains only meaningful concepts. But a formulation as general as this undoubtedly requires elaboration. So I turn to a series of comments. The influence of the Western philosophical tradition is so pervasive that almost everybody will ask whether such undefined terms as, say, 'green' and 'between' should be taken to refer to characters of physical objects or, perhaps, to those of "subjective" givenesses, the sort of things philosophers call sense data and percepts. Whoever asks this question raises, in effect, the classical realism issue. If one wishes to clarify this and other traditional philosophical puzzles, then it is indeed necessary to trace all our concepts "down" to "subjective" data. On the other hand, it is rather obvious that if one merely wants to analyze the structure of physical science, it is sufficient to assume that the undefined concepts in terms of which all concepts of physical science are defined refer to some immediately observable properties of and relations between physical objects. To the situation in psychology I shall attend in the next section. I t may be well to call attention to the breadth of the proposed criterion of meaning. Consider, for instance, the concept 'centaur.' A little reflection shows that to define 'centaur' or, as one ordinarily says, to describe a centaur is no more difficult than to describe, without the use of pictures, an okapi so that somebody who has never seen an okapi will, when he does chance upon one, recognize it. Thus, the concept 'centaur' is meaningful and so is, therefore, the statement 'There are centaurs (Centaurs exist),' though we have, of course, overwhelming reasons to believe that this statement is false. Or, to show the range of the criterion in another direction, take the statement 'A million years after the last man has perished, the temperature of the sun will be 3.000 centigrades.' Though nobody will be around at the time to make a measurement, the statement, since it contains only meaningful concepts, is meaningful. This is entirely as it should be; for physicists do make assertions of this sort, provided only that they can infer them from observations they now make in conjunction with laws that have been established by earlier observations. I have hinted before that 'concrete,' 'abstract,' 'simple' and 'complex' do not recommend themselves as candidates for technical terms. Now I am ready to show some of their ambiguity. Sometimes, it appears, concepts such as 'electric field' or, in psychology, 'habit strength' are called abstract because the chain of definitions that leads to them is rather long.2If this is what one means by 'abstract,' then he must also grant that 'combustion engine' is a very abstract concept. Yet there is a second connotation of the term which would lead many to insist that 'combustion engine,' though very complex, is not abstract. Behind this objection lies the habit of calling abstract all concepts whose referents are not physical objects (material things) and concrete only the names of kinds of physical objects, whether they are as "~imple'~ as stones and trees or as "complex" as combustion engines. With this connotation, it is worth noticing, every Length, as here used, is admittedly not a very precise notion. But neither is abstractness.

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relational concept becomes abstract, no matter whether the pattern (synonym: configuration) it names is so complex that its name, the concept, requires a long chain of definitions; or so simple that, as in the case of some spatial and temporal relations, its name is undefined. This goes to show that everything that can be said by means of the four terms under review can be said more clearly without them. The value of this clarification will be seen presently, when I shall try to dispel the confusion that surrounds the term 'hypothetical,' in the sense in which some writers believe that certain concepts are hypothetical. 4. Behaviorism. The methodological study of psychology begins with two questions. (a) What can be said about the undefined concepts in terms of which the concepts of the science of psychology are defined? (b) What, if any, are the special rules or principles to be observed in framing these definitions? Who has answered these questions and explored the implications of his answers has, in substance, the first chapter of his philosophy of psychology, a chapter, by the way, for which the title of this essay could well serve as a heading. Behaviorism, as I here use the term and in the sense in which I, like virtually all positivists, am a behaviorist, is the position that gives the following answers. (a) All concepts of the science of psychology can be defined by means of the class of undefined concepts that enter into the definitions of physical science, i.e., the names of some immediately observable characters of physical objects. I n other words, there are no undefined concepts that are specifically psychological in the sense of being indispensable ingredients of some psychological concepts and of psychological concepts only. (b) There are, on the level of methodological generality, no rules or principles, to be observed in the framing of psychological concepts, which are specifically psychological in the sense that these rules or principles would not also belong to the logic of concept formation in all other sciences. I need not, I trust, at this late date make once again the general case for behaviorism; so I shall merely add two comments that serve my specific purpose. A psychologist may say of one of his subjects that he is seeing green, or that a certain response has in him a certain habit strength, or that he has a certain personality trait. The three italicized t e r n are psychological concepts and, since none of them refers to an immediately observable character of physical objects, it follows that they are, upon our view, defined concepts. The same is, of course, true of virtually all psychological concepts. Presently I shall, as a basis for d further explanations, investigate the logical structure of one of these definitions or, as one also says, I shall "construe" one psychological concept. The one I have chosen is 'seeing green,' which is, logically speaking, one word and, of course, not the same as the undefined concept 'green.' There are two reasons for this choice. First, the logic of this concept is, in spite of its "mentalistic" flavor, exactly the same as that of such typically behavioristic notions as 'excitatory potential' or 'habit strength'. Second, because of this flavor I shall be able to take up without further ado some points of traditional interest. I t thus follows from the behavioristic position, so felicitously stated by Max Meyer when he said, long ago, that psychology is the psychology of the other

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fellow, that no undefined concepts except those of a class P , exemplified by physical objects, are needed to construe 'seeing', 'knowing', 'remembering', as we apply these and similar terms to our subjects. But this does not imply that if one wishes t o analyze the philosophical puzzles or, what amounts for a positivist to the same thing, if one tries t o construe the whole of our language directly, not behavioristically, one can still do this with the same class P of undefined concepts, Just as it is sometimes necessary for such purposes to conceive of the undefmed terms as referring to "subjective data" rather than to physical objects, so it may well be that for some such analyses the class P must be supplemented by additional undefined terms ( l ) ,perhaps even such terms as 'seeing,' on whose introspective irreducibility within the framework of prebehavioristic psychology tho advocates of the act insisted. I n this paper, with its limited purpose, I shall only once (section 8) have to asstme that Lhe undefined concepts in terms of which the psychologist construes all others refer to his data (i.e., the psychologist's, not his subject's!) rather than to physical objects. Characteristically, this is in the one section that deals with an epistemological rather than a methodological issue; and even there I shall arrange my argument so that 1: shall get along with the concepts of P. 5. Definitionsin use. There is no structural difference between the definition 3f 'seeing green' on the one hand and that of a physical concept such as, say, 'electric field' on the other. I n order to show this, I shdl have t o begin with a few remarks about the gammatical form of definitions in general. Those of us who have not made a study of the matter usually think of a definition as an equation with the new or defined term on the one side of the equality sign, conventionally the left, the defining term or phrase on the right, and the idea that the two sides mean the same thing by verbal agreement, i.e., by a convention about the use of words. ' n = 3.1415 . . .' is, perhaps, a good illustration. The illusion that all definitions are of this simplest form is increased by the fact that in the case of a quantified concept--e.g., when we define density

( : nically, however, this equation is only one of the several clauses of the complete as the quotient of weight and volume-we

write an equation d

=

--

definition. If they are fully expanded, then the overwhelming majority of all useful definitions in science are of the following form. The idea of the equationlike balance between the left and the right side is, of course, correct. But both the left side, L, and the right side, R, are sentences, not terms or phrases; and what we informally think of as an equality sign is, therefore, better read as 'means by verbal agreement the same as'. The left side, in particular, does not consist of the defined term in isolation but of the sentence of the simplest possible structure in which the defined term occurs. I n the case of 'electrical field' for instance, if we restrict ourselves to a qualitative notion, L reads 'This place is in an electric field.'3 The right side, R, is, more often than not, a compound sentence. I n our illustration it reads, 'If R1, then Rz,' where R1 stands for 'An Idiomatically one would rather say 'There is a n electric field a t this place.' I n the next section I shall show t h a t logically this is very misleading.

electroscope is a t the place (of which L asserts that it is in an electric field)' and Rz for the description of the behavior of the electroscope (in an electric field). Technically such definitions are known as definitions in ztse, the reason for this name being that L is a sentence in which the new term is used. I t will be noticed that I have already produced a schematic definition of 'electric field.' One frequent objection t o the adequacy of this sort of definition claims that it does not do justice to all we mean by 'electric field'. I t is said, for instance, that there are many other "tests"; that the description of any one of these could equally well serve for I?; and that this very fact, together with other laws about electric fields, belongs to the meaning of 'electric field'. T o this I would answer that what a biologist means by 'apple' is exactly what a tenyear old means and that what our objectors have in mind is more clearly and less dangerously expressed by saying that the biologist knows more about apples than the child. T o be sure, then, I, too, can say what our objectors want to say. The danger of their way of saying it is that they introduce, without noticing it, a new meaning of 'meaning.' And the consequences of unnoticed ambiguity make s sadly familiar story. Thus I shall insist that the whole meaning of a defined concept resides indeed in the right side of its definition. Psychological readers, who of late have heard so much about operationism and that a concept, to be meaningful, must be operationally defined probably have wondered for some time whether t,he definitions whose study I consider such an important part of the philosophy of science are operational and, if so, why I have avoided the term. The answer to the first query is as follomrs. The conditions under which a concept is meaningful have been stated above (section 3) and nothing needs to be added. However, a very large number of definitions in science show a certain feature that has been the occasion of the new name for an old thing. Take again our illustration. Here R is of the form 'If R1 then Rz9 and R1 describes a state of affairs often not realized when there is, in fact, an electric field but which we, if we wish, can bring about by manipulating our environment. Rt, on the other hand, describes what happens, without any further doing of our own, whenever what R1 mentions is the case and the sentence L is to be considered true. Thus, while literally speaking all definitions are purely verbal, it is true enough that in some cases, whenever we want to ascertain the truth or falsehood of L, we must help nature along by realizing manipulatively what R1 mentions. As for the terms 'operationism' and 'operational,' they have the merit of emphasizing this important feature. On the other hand, they did help to create the impression among scientists that this one feature is the whole of the empirical philosophy and, also, they have been at least one of the causes for some curious misunderstandings (see section 7). What needs to be said about psychological concepts can, after all these preparations, be said very briefly. The standard behavioristic schema for the definition of our paradigm, 'seeing green', is clearly a definition in use. L reads in this case 'Sis seeing g~een';R is of the (operational) form, 'If R1 then Rz7,where R1 stands for the description of an experimental set-up (with the subject in it), in which the subject's color vision is being tested and Rz for the description of

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a certain kind of behavior which the subject may or may not display. If he does display it then we say, by definition, that he is seeing green; if not, that he is not. I t follows that whenever we are faced with a methodological question about a psychological concept we may profitably ask what becomes of that question in physical theory. If, for instance, it is said, either in criticism or othenvise, that some psychological concepts are symbolic constructs, or fictions, or hypothetical, we shall do well to inquire what sense, if any, it makes to say such things about friction coefficients, electric currents, and magnetic fields. 6 . Defined Concepts not Hypolhetical. Recently we were told (7) that toughminded psychologists still use "words such as 'unobservable' and 'hypothetical' in an essentially derogatory manner [and] that 'fictions' and 'hypothetical entities' are sometimes introduced into a discussion of theory with a degree of trepidation and apology quite unlike the freedom with which physicists talk about atoms, mesons, fields, and the like," while on the other hand there is also a tendency toward "arguing that if neutrons are admissible in physics, it must be admissible for us to talk about, e. g., the damming up of libido." I t will be noticed that the authors mention not only fields but also the particles of atomic theory, i.e., those entities which we tend to visualize as physical objects more or less like tennis balls, only too tiny to be seen and, in this sense, unobservable. If I am right in maintaining that all psychological concepts are, at most, of the logical complexity of 'electric field,' then the elementary particles need not at all be brought into a methodological discussion of psychology. However, they have been brought in; they are best construed in a way that has, in a very special sense of the term, been called hypothetical; attempts have been made to construe psychological concepts in analogy to them. In my opinion, all this adds up to one big confusion. While I shall not ignore it, I shall at least try to keep my own argument straight by relegating a brief discussion of these matters to the last section. For the rest, then, the point seems to be that in physics such concepts as 'electric field' are hypothetical and yet legitimate beyond question and that, therefore, psychologists should also be allowed to introduce concepts of this-in the eyes of some, dubious-status. This, too, is very confusing to me. For, as I shall now try to show, there is no clear meaning of 'hypothetical', except one in 'ivhich the assertion is as obvious as it is non-controversial, in which it \vould make sense to say that either 'electric field' or 'seeing green' are hypothetical. Thus there is no issue; and where there is no issue there is no argument, either pro or con. Before leaving the house in the morning I usually reach into my pockets to check whether I have my watch. If I do not find it, I make the hypothesis (synonym: assumption) that it is in the upper left drawer of my desk. SO I retrace my steps, open the drawer and, as the ease may be, either confirm or disconfirm the hypothesis by direct inspection. Notice, first, that what is hypothetical is not the watch but the statement 'There is a watch in this drawer' and, second, that this watch is not unobservable but merely, at a certain time, unobserved. Some hypotheses, of course, cannot be decided directly; we would have to go too far, or dig too deep, or live too long, or what not. In such cases,

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like the one about the temperature of the sun after the extinction of man, we often arrive at a decision indirectly from what we observe directly in conjunction with laws we assume to be true. But whatever the hypothesis is about, a watch, a temperature, or what not, it is always about a kind that can be observed. The statement 'There are centaurs' is essentially of the same type as that about my watch; the only difference being that in this case we must, as it were, scan the whole universe before we can be sure that it is false and that, if there were several centaurs, observation of any one of them would provide us with direct confirmation. 'There are centaurs' is often expressed by 'Centaurs exist.' This is the reason that such statements, which illustrate the first meaning of 'hypothesis,' are sometimes called existential hypotheses. However, 'existence' and 'existential' are highly ambiguous philosophical terms. Philosophical realists, for instance, claim that we may from our experience infer the "existence" of an "unobservable" real world and sometimes call this sort of "inference" an existential hypothesis (6). Clearly, existential hypotheses, in the ordinary sense of the term which I have just explained, are not "existential hypotheses" in this controversial, philosophical sense. The second meaning of 'hypothetical' is synonymous with what philosophers mean by 'inductive.' Laws of nature are generalities, i.e., they are of the form 'Whenever A then B, where 'A' and 'B' refer to kinds of situations; e.g., 'Whenever a metal object is heated then its volume increases'. Since we do not and, in principle, cannot test all its instances, a law always asserts more than we have actually observed. Empirical philosophers feel that no matter how well established a law may be in practice, this gap, this difference in certainty between a generality and its instances cannot be bridged. Technically speaking, a law of nature is, therefore, always an assumption or, if you please, a hypothesis. ,And, by the way, as I suggested in the last paragraph, negative existential hypotheses ('There are no centaurs') are in this respect like generalities. This is the second meaning of 'hypothesis' and 'hypothetical' which I can understand. For a third, consider the following situation. The incidence pattern of a new disease may lead pathologists to suspect that ft is caused by a bacillus. Investigations designed to test this "hypothesis" will either confirm or disconfirm it. Confirmation consists in the establishment, within the omnipresent limits of inductive uncertainty, of an empirical law, namely, that in patients showing the clinical syndrome of the new disease certain bacteriological tests always yield positive results. What we thus assume or hypothesize when we entertain a hypothesis in this sense is a law, or a kind of law, not from any of its instances but, rather, from other laws already established; in our illustration, the law that diseases caused by bacilli spread in a certain way. Except for the one to be discussed in the last section, these three are the only clear meanings of 'hypothesis' and 'hypothetical' of which I can think. The right sides of some definitions contain either one or several generalities and negative existential statements. In some definitions this feature appears only after all defined terms have been eliminated from IZ. Whenever it does appear, the truth of R cannot be conclusit~elyestablished by a finite number of

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observations and, since L always means what R means, neither can L, though this latter statement is not explicitly either a generality or a negative existential statement. This is what I had in mind a while ago when I mentioned a sense in which some concepts may indeed be called hypothetical. I have called this sense obvious because it is but another aspect of induction; and I have called it noncontroversial because I am convinced that this is not what people mean when they insist that certain concepts are hypothetical. But if I am right, then there is no other good sense of the term in which any concept could be called hypotheticd.It is time, then, to inquire into the meaning of those who do not agree with this (6, 7'). A little reflection shows that the concepts which these writers single out as hypothetical are all abstract in several meanings of this ambiguous notion: they do not refer to physical objects; they are defined concepts; relational terms, particularly those of space and time, are prominent in their definitions. There is, of course, no objection against using 'hypothetical', in a further meaning, as a label for all or some of these features. But again I believe this is not what these authors intend. What puzzles them and what they wish to express by calling 'electric field' hypothetical is that though they are convinced that electric fields "exist", t h e i cannot "see9' them as they can see chairs, stones, and other physical objects. In other words, they equate 'hypothetical' with 'unobservable'. Now, I have hinted before that 'unobservable' is used by realistic philosophers and that, as they use it, the "real9' chair is as unobservable as an electric field. If this is what is meant, then why confuse the issue by singling out certain "abstract" concepts as hypothetical? On the other hand, it seems obvious to me that as long as one steers clear of such questions and uses 'seeing' and 'observing' with their ordinary meanings, electrical fields, far from being unobservable, are actually seen and observed. For I do not think anybody will deny that we can observe electroscopes and their behavior. Yet these are the only things mentioned in the right side of the definition of 'electric field'. Since, as in all definitions, the left side L and the right side R mean exactly the same, it follows that whenever we see the pattern mentioned in R we also see an electric field. What holds for 'electric field' holds for all other defined concepts; nor do I need to repeat that this includes all psychological concepts. If the right side R of a definition D contains itself a concept C claimed to be "unobservable," one merely has to expand D by substituting for C its definition. By repeating this elimination procedure as often as necessary one can always obtain an R that mentions only characters of the kind that have called immediately observable. I conclude, then, that there is no specific sense in which any defined concept refers to an "entity" whose "existence" we "hypothesize." Since the point is of prime importance, I should not like to leave it without calling attention to a feature of our idiomatic language that lends some specious plausibility to the ,~ mistaken belief that there is such a sense. As I have pointed out b e f ~ r ethe left side of the definition of 'electric field' (and of some other concepts) may be rendered idiomatically by 'There is an electric field at this point'; thus it seems to have the form of an existential hypothesis such as 'There is a watch in this

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desk'. Logically the left side of this or any other definition does not have this form; and it does, therefore, not really assert the existence of some thing, of the unobservable kind called 'electric field', in the sense in which 'There is a watch in this desk' asserts the existence of some thing of the observable kind called ' ~ a t c h ' . ~ 7. Defined Concepts not Constructions. Ever since Betrand Russell a t the turn of the century first recognized its significance, the device of clarifying the status of many concepts by first construing them as defined and then clarifying the logic of their definitions has played a major role in all empiricist or, if you please, positivist philosophizing. Criticism, both methodological and epistemological, has in the main followed two lines. The one insists that this mode of analysis makes many concepts or, rather, their referents hypothetical. What needs to be said on this head I just finished saying. The other major objection feels that our analysis distorts the nature of things by making many concepts or, again, their referents constructions. The connotations of 'construction' in this context are arbitrariness, artificiality, and subjectivity. The charge of arbitrariness is probably caused by the freedom we actually have in defining concepts; what it overlooks is that it is a matter of fact, not of choice, linguistic or otherwise, whether a defined concept is exemplified and, if exemplified, useful. The charge of artificiality harks back to the controversies about the status of so-called analytical introspection, which divided psychologists at the time of Wundt and Brentano; it overlooks that while introspective analysis is one thing, linguistic analysis is another, entirely different thing. But it is the third of these charges, the one I labeled subjectivity, which I wish first to explain and then to refute; partly because it has recently reappeared in a very lucid and, therefore, to me very attractive paper (6) on our subject. So I shall make the general point in the special form suggested by its authors. Briefly summarized, their argument proceeds in three steps. First, they warn that the stress on the scientist's manipulations must not mislead us into the belief that he actually creates through these manipulations what he "operationally" defines. In terms of that common-sense realism which we all share and which is not a philosophical position, the edge of the table is there and has a definite length, whether or not we manipulate yardsticks in order to ascertain it, just as we all have our B-coefficients though nobody will ever care to compute them. Nor is, in the case of the edge, this manipulation, if we perform it, that of the artisan who made the table. This emphasis is, in my opinion, very just and, obvious as it seems, not quite unnecessary. Of course, if one puts the matter as plainly as our authors do and as, borrowing their illustration, I just did, then it becomes patently absurd to say that we make or construct what we operationally define. Yet there is a certain pattern of verbalizing, on the philosophical level as it were, this "operational" feature, which does leave the impression that we make or construct whereof we speak, in some unclear philosophical This is not to say that genuine 'There are'-statements (existential hypotheses) may not occur in R . But after expansion one sees that these are all about particulars or about kinds that are immediately observable. For a more technical treatment of this point see (9).

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sense of 'make' and 'construct' which fully justifies the charge of subjectivity. Historically, this pattern stems from Hegelian idealism; in contemporary thought it persists in Deweyan instrumentalism; its (partly wholesome) influence on the development of psychology becomes apparent in Dewey's reflex arc paper of 1896, which was the opening shot of functionalism. Rereading this cIassical document, the contemporary psychologist, who has not read it since his salad days, if he read it then, will appreciate this allusion to the general history of thought which I cannot take time to expand. Be that as it may, in spite of some superficial similarities, positivism is not instrumentalism; that is why I can so heartily agree with the first step in our authors' argument. Perhaps, this is also the best place to make a terminological point. I t is in order to avoid these "constructionist" connotations that I no longer use the currently fashionable 'empirical construct' as a synonym for 'defined concept.' Second, the authors remind us of some obvious truths. Psychology, like all other sciences, seeks to discover laws. A law, typically of the form 'Whenever A then B', connects at least two different variables; psychological laws, in particular, connect variables of the two kinds called stimuli and responses. In their actual work behaviorists, like all other psychologists, try to find and sometimes do find such laws. However, and this is the third and crucial step of the argument, this is not, according to our authors, what the behaviorist says he does when he advocates his "operationist" philosophy. Take, for instance, the laboratory situation which I have used for a schematic definition of 'seeing green.' What is being manipulated or operationally defined, our authors insist, is the stimulus situation and the stimulus situation only; the behavioristic account errs, therefore, in trying to constitute the response, too, in terms of these operations. If this could actually be done, the response would be nothing but the stimulus all over again, in violation of the obvious requirement that a law must connect a t least two variables. To show the fallacy in this argument, assume that after a bag of potatoes, called S, has been put in the place of the subject in the aforement-ionedlaboratory situation, we are asked to determine the truth or falsehood of 'S is seeing green'. Since this sentence is the left side L of our definition in use, we turn our attenion to the right side R, which as we remember is of the form 'If RI then Rz'. RI describes a situation which we can manipula,tively realize. In fact, we already began realizing it when we put S in the place usually reserved for more conventional subjects; now we fully realize it by uttering certain instructions, turning on some switches, etc. Our authors are quite right in insisting that when we have done all this we are through manipulating. But they overlook that after we have realized what is mentioned in R1 we decide that S is seeing green if and only if we observe that what Rq mentions actually takes place without any further doing of our own. In the case of the potato bag, for instance, we will arrive a t the conclusion that it is not seeing green. So I don't know in what sense it could be said that the behaviorist account errs because it omits the response, futilely trying to reconstitute it in terms of the stimulus. Yet one can, I believe, with some confidence identify our authors' frame of reference and, in this sense, under-

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stand their argument. Responses as they conceive them are, I submit, typically and fundamentally the subject's conscious contents, in the case a t hand a socalled sense datum. Behaviorism does not literally concern itself with such response^^^; SO our authors are led to believe that the behavioristic analysis cannot, in principle, account for the response. What is thus under attack is not so much the current "operationist" formulation but, rather, the very core of behaviorism itself. If this interpretation is correct, then there is still some point in including in a paper like this the topic which I shall take up next. 8. Other Minds. Everybody believes that the subject of our experiment in color vision has a green sense datum; or, as I shall briefly say, everybody believes in a common-sensical way that other minds exist. Hardly anybody nowadays takes seriously Watson's occasional extreme statements which seem to deny this homely truth. The position one can defend and which I , for one, am prepared to defend is this. (a) Though he ignores, literally speaking, his subjects' minds, the behaviorist can, in a certain sense, say about them everything anybody could conceivably have the occasion or the desire to say. (b) If he wanted to, he could also without violating his meaning criterion quite literally speak about other minds. (c) If he does not choose to do so, it is because such statements are and always will be scientifically useless; except, perhaps, in a provisional and heuristic sense which is, of course, not controversial. To begin with (a), our definition of 'seeing green' shows that we, too, can say a person is seeing green whenever a '(mentalistic" theorist thinks that this is the case. What goes for 'seeing green' goes for all other mentalistic formulations. To deny that the behaviorist can in this sense know and say everything about other minds-provided only his science is as well developed as, in principle, it could be-is to cling to the belief that some mental states do not have phsyical correlates. The evidence that there are no such states is, of course, overwhelming. But, then, no fact of this kind is ever completely beyond doubt. Speculative philosophers wishing to hope against hope are, therefore, free to do so; only, I should not care to argue with them. On the other hand, I am, as a philosophical analyst, very much interested in another argument, in connection with (b), which insists that what has been said so far does not yet square completely ~ with common sense. "To be sure," so this argument goes, "you can s a what other people say, but you do not really mean what they mean; so it is all but a clever verbal trick. Take again your definition of 'seeing green'. You yourself insist that all you mean, when you assert L, is R. What common sense means and wishes to assert in the same situation is expressed by 'If R then L1', which is not a definition, where Ll says that there is something green, namely, the subject's sense datum, and where, therefore, 'green' is the same undefined concept that appears in the description of the stimulus in R." This argument, I believe, has force; my answer is, therefore, that 'If R then L1' is indeed meaningful according to the meaning criterion for sentences (section 3). T o show this, assume that I serve as the observer in our experiment and that my statement R has been analyzed "down" to my contents. In this language all proper names refer to so-called sense data and 'green' to a quality of such data. In this Ian-

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guage I now formulate L1 as follows: 'There is something that is green and different from a,' 'a' being the proper name of the datum I receive from the stimulus and which, by assumption, is the only green datum I have at the time. It should be clear that L1 asserts, no matter how roughly and schematically, the existence of the subject's mind. Also, it is easily seen and, by transcription into a formal language, as easily proved that Ll is grammatically correct and except for the meaningful concept 'green' contains only structure words. Thus L1 is meaningful and so is, therefore, since R is meaningful, also 'If R then L1'. I may, therefore, whenever I assert R, also assert the "corresponding" sentences 'L1' and 'If R then hil.' The facts are so that this will never lead either to a contradiction or to any other difficulty. Only, the facts also are so that all the evidence I shall ever have for statements of these two types will always be completely described in the corresponding R-statements. But this is exactly what (c) maintains. The common-sense statements about other minds are not, according to the formulation I have given to the meaning criterion, meaningless; but they are, except perhaps heuristically, scientifically useless. 9. T h e Locus of Psychological Concepts. I turn now from the mind to the body. For the apprehension that the way in which positivists construe psychology is either incomplete or othenvise one-sided is, I fear, not limited to advocates of the mind whose intellectual roots, if they are psychologists, are, as one would expect, in the phenomenological tradition. I t is my impression that, at the other extreme, psychologists whose main interest lies in the area known as physiological psychology sometimes suspect us of an antiphysiological bias. The best way to face this issue is to face the question "What is the locus of defined psychological concepts?" where 'locus' means, literally, a place in space and the range of concepts extends from those used by Hull and Tolman to such mentalistic ones as 'seeing green.' The answer my physiological friends want to hear in most cases is9 quite obviously: "In the brain." Or, as I had better say, this is the kind of answer they expect; for nobody asks nowadays a methodologist to take a stand on such scientific matters of fact as those at issue between central and peripheral theories. Correspondingly, no competent positivist believes that the validity and value of what he has to say depends on such issues of, relatively speaking, scientific detail. So I shall consider this anslver, "In the brain," without prejudice and simply as a way of speaking. Nonliterally and on the level of scientific common sense as it were, I would say, then, that I , too, would give this answer. But I hurry to add that the whole virtue of logical analysis consists in that literalness which exhibits the precise meaning of what common sense justly believes but, more often than not, inaccurately and misleadingly states. In this sense both question and answer need analysis and restatement. Consider the statement which says that a certain physical object 0 is heavy. Since 0 , being a physical object, has a topographical locus, and since the character 'heavy' is predicated of 0 , 0's heaviness or, as one usually says, gravity has in this indirect sense a topographical locus. But to ask further where in 0 its gravity resides is, literally, a meaningless question. This is so in spite of the fact (which caused me to choose this illustration) that \Ire all incline to say that

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0's gravity resides in its center of gravity C. What is meant by this inaccurate statement is precisely expressed by the rules that tell us how to determine @ and by those lam-s that tell as in which respects O behaves as would a very small object, with the same mass as 0 , if it were placed at C. As always, d a t holds for physics holds for psychology. 'Seeing green' or 'having a certain habit strength' are predicated of organisms. Since organisms are physical objects in space, their seeing green or their having a certain habit strength are, in this indirect sense, localized. But, to be sure, this is not what my physiological friends want to hear; they are interested in what one usually calls the neurological basis, to be precisely and specifically determined within the organism, as the laxs of physics precisely and specifically determine an object's center of gravity. I conclude, therefore, that as in the case of physics they are looking for laws; in particular, for 1a.lr.s of the type 'Whenever A then B9where 'A' stands, in our illustration, for 'S sees green' and sB'is the description of what happens in certain parts of S's organism whenever he sees green. If we believe that suclt laws will eventually be found for all psychological concepts, we entertain a hypothesis, in the third sense of the t e r n (section 6), the one I have illustrated by the hypothesis that a certain syndrome is caused by a bacillus. Now I am so far from being antiphysiological that I don't mind saying that not to entertain this hypothesis, at least in a general manner, is tantamount to believing in ghosts. But, having said that much I must also insist on two more things. First, the meaning and the usefulness of such a concept as, say, habit strength does not depend on looking for or having found the kind of lan- about it in which physiological psychologists are, quite legitimately, interested. Second, 'A is B' or 'A is the locus of 13' are very misleading ways of expressing what is correctly expressed by 'Whenever h then B.' In my earlier illustration nobody would dream of saying that the syndrome is the bacillus or that the bacillus is the locus of the syndrome. Yet this is exactly as one uses his words when he says that S's seeing green is a state of his brain or that habit strength as, say, Hull defines it, has a physiological locus, This should convince everybody that this way of speaking is, to put it mildly, not very helpful. One reason I have dealt with this point at some length is that the authors of a paper (7) I have mentioned before propose to call sonze psychological concepts hypothetical in an existential sense. As fas I understand them, these are simply the concepts about \\-hose physiological correlates they are more sanguine than about those of some others. Concerning such use of 'hypothetical,' I shall merely ask t~ o questions. First, do we in our earlier illustration call the syndrome itself hypothetical because n-e expect it to be caused by a bacillus, or as long as we haven't found that bacillus? Second, don't we expect to find eventually the physiological correlates for all psychological concepts? As for their use of 'esistential', our authors are apparently influenced by that sort of philosophy (5) that considers the elementary particles of physics as unobservable hypothetical entities in a realistic sense; the mistaken analogy is then between these particles on the one hand, and, on the other, those as yet unobserved brain states which are studied in physiological psychology. This brings me to my last point.

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10. Minds and Particles. No good purpose, either methodological or epistemological, is served by construing any psychological concept in analogy t o the elementary particles of physics. To show this it is not necessary to bring in protons and mesons; the logical heart of the matter can be discussed by means of an illustration as simple and archaic as Newton's corpuscular theory of light. The basic idea of this theory is contained in the following statement: "Whenever you see a ray of light, assume that there is in its place a beam of little objects (particles) smaller and faster than we could ever see and which obey the laws of mechanics." This s e n t e n c e 1 shall abbreviate it 'Whenever E, assume H'contains three key phrases. I have italicized them and shall make my points by explaining them. To begin with the obvious, the scientific gist of the theory is contained in the last of these phrases, which stipulates that the particles obey the laws of mechanics. Consequently, one can translate a statement El of optics into a statement HI about particles, apply to these particles the laws of mechanics, and retranslate a new statement H z thus obtained into a statement Ez. The net result, 'Whenever El then Ez,' does not mention particles and has the form of a law of optics. If this law actually holds, then the theory works t o that extent; a law of optics has been "derived" from mechanics. For instance, the rectilinear propagation of light in a homogeneous medium follows in this fashion from the law of inertia. Turning to the second phrase, which stipulates that the particles are smaller and faster than we could ever see, we notice first that 'H' is a hypothesis in the first meaning of the term (section 6), i.e., it is a 'There are'-statement like 'There is a watch in this desk' or 'There are Centaurs.' The next question, then, is whether the kind of things it mentions is observable in the sense in which 'watch' and 'centaur' are the names of observable kinds. Now it seems that this question must immediately be answered in the negative since me introduced the particles as smaller and faster than we could ever see. However, if we take, as we must, our criterion literally, then this answer is, perhaps, not unavoidable. Technically, the question is merely whether we can define dimensions as extreme as those of the particles in terms of characters that do refer to immediately observables. If a few points are stretched, this probably can be done. One who wants to argue this case could say, for instance, that if 'inch' is a meaningful concept then so is 'a trillionth of an inch', since $he latter adds to the former only a purely arithmetical, and that means logical, idea. Let us call this interpretation the Jirst way of construing the particles. If it is adopted, 'H' becomes meaningful without further ado; and instead of writing 'Whenever E, assume H' one can simply write 'Whenever E then H.' We notice the similarity between 'Whenever E then H' and 'Whenever R then LIy,the statement we encountered in section 8. And just as the meaningfulness of this latter statement reveals the basis of the common-sense belief in the existence of other minds, so the former may be cited by those who feel the urge to say that particles are as real as chairs. Notice, though, that I did not say 'real' but merely 'as real as chairs'. For what realistic philosophers mean when they speak of the real, unobservable object is something different, which can and must be thrashed out in terms of such ordinary physical objects as stones

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and chairs, without confusing the issue by appeals either to the prestige or to the complexity of science. In other words, even if the particles could be construed in the first way, it would still not follow that they are real in the sense in which some philosophers think that they are. Aside from its own difficulties, the first way of construing the particles is, in fact, extremely clumsy and unsatisfactory, because it does not provide us with efficient tools to clarify the numerous peculiarities and logical difficulties of the theory of matter.6 Fortunately, there is a second way of construing the particles, which I have in my schema indicated by the word 'assume.' I t is with reference to this second way of construing them that the particles are sometimes called hypothetical entitites and the theories in which they occur models. This is the fourth intelligible meaning of the term 'hypothetical'. There would be no point in giving here a detailed account of this second way and for a few hints to be helpful the matter is much too intricate. The gist of it is that upon this construction 'Whenever El assume H' is no longer a definition but, rather, the schema of another logical technic, also known as the partial interpretation of a calculus. Having said so much about physics I can again be very brief about psychology. The first way of construing the particles introduces nothing logically new. It is, therefore, hard to see what could be gained by insisting on the analogy between psychological concepts and the particle notion. If, on the other hand, the analogy is pressed too hard then it is either unnecessary or misleading. If it is intended to insure the existence of other minds, the idea being that I know of your data as I know of particles, then we have seen (section 8) that this can be achieved much more simply. Thus the analogy is for this purpose unnecessary. If it is meant to suggest a direct or functional similarity between brain states on the one hand and the microstructure of all matter, whether brains or stones, on the other, then it is clearly misleading. As far as the second way of construing the particles is concerned, I cannot, of course, here go through a list of all psychological concepts in order to prove that there is not a single one among them that cannot be satisfactorily construed as a defined concept, i.e., without use of those elaborate technics. As I have said before, I believe that this is in fact so. But it is well known that one cannot, in a certain sense, prove a negative case. So I shall rest mine until I am shown that I am mistaken. To say that it is not necessary to construe our subjects' conscious contents or, if you please, their unconscious wishes as we construe the particles of physics is one thing. To say that it cannot be done is another thing. I see no reason why it could not be one; and I am sure that if it is done carefully one can avoid the confusions that beset the careless way of talking about this possibility. But, For a detailed discussion of particle theory see (4) and the references there given. T o mention just one point, it does not make sense t o say t h a t the elementary particles are in all respects like physical objects since we actually "see" or "observe" them individually, e.g., by watching a scintillation screen. The statement 'A particle is a t this place,' made on such an occasion, is the left side of a very complex definition whose right side describes the experimental set-up. The name of a physical object, on the other hand, is typically a logical simple.

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4 repeat, there is no question, either methodological or epistemological, about a psychological concept that cannot be answered without this complicated exercise. And I would also argue that we do not understand any such question fully if we do not, among all possible answers, recognize the one which is simplest.

State University of Iowa REFERENCES 1. Bergmann, G., "Logical I'ositivism" in V. Ferm (ed.), A History tems, 1950, New York, pp. 471-482 2. ---, "Semantics" ibid., pp. 483-492

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Philosophical Sys-

3. ------- , Remarks on Realism. I'h~los. Sci., 1946, 13, 261-273. 4. ------- , T h e Logic of Quanta. drner. J . Physics, 1947,15, 397-408,497-508. 5. Feigl, H., Existential Ilypotheses. Philos. Sci., 1950, 17, 35-62. 6. Israel, H. and Goldstein, B., Operationism in Psychology. Psychol. Rev., 1944, 51, 177188. 7. MacCorquodale, K. and hfeehl, P. E., On a distinction between hypothetical con.structs and intervening variables. Psycho$. Rev., 1948, 55, 95-107.