OPERATIONISM IN PSYCHOLOGY: WHAT THE DEBATE IS ABOUT, WHAT THE DEBATE SHOULD BE ABOUT*
ULJANA FEEST
I offer an analysis of operationism in psychology, which is rooted in an historical study of the investigative practices of two of its early proponents (S. S. Stevens and E. C. Tolman). According to this analysis, early psychological operationists emphasized the importance of experimental operations and called for scientists to specify what kinds of operations were to count as empirical indicators for the referents of their concepts. While such specifica-tions were referred to as “definispecifica-tions,” I show that such definispecifica-tions were not taken to con-stitute a prioriknowledge or be analytically true. Rather, they served the pragmatic func-tion of enabling scientists to do research on a purported phenomenon. I argue that historical and philosophical discussions of problems with operationism have conflated it, both conceptually and historically, with positivism, and I raise the question of what are the “real” issues behind the debate about operationism. © 2005 Wiley Periodicals, Inc.
The term operationism(or operationalism) is commonly associated with the Harvard physi-cist Percy Bridgman (1882–1961), who famously claimed that “in general, we mean by a concept nothing more than a set of operations; the concept is synonymous with the corresponding sets of operations” (Bridgman, 1927, p. 5). While the notion of operationism was never very influential within physics, it gained a fair amount of popularity within psychology and the social sciences (Smith, 1997, p. 668). Even today, the notion of operationism plays an important role in psychol-ogy, with many introductory textbooks on psychological methods devoting a section to opera-tionism. However, over the years there has also been a sporadic but ongoing debate about the na-ture and tenability of psychological operationism. After varieties of this position were first formulated and elaborated on by Stevens (1935b, 1935c, 1936, 1939a) and Tolman (1936/1958f, 1937, 1938/1958d), a number of papers appeared in the Psychological Review (Bergmann & Spence, 1941; Israel, 1945; Israel & Goldstein, 1944; Pennington & Finan, 1940; Waters & Pennington, 1938; Weber, 1940), critically discussing the vices and virtues of this position. This debate culminated in a symposium on operationism, organized by the Psychological Review
(Boring et al., 1945). A decade later, another philosophical symposium was devoted to the issue (Frank, 1956). During the same time period, the notion of operationism underwent certain modi-fications within psychology (Campbell & Fiske, 1959; Garner, Hake, & Erikson, 1956). The no-tion of operano-tionism was once again discussed in the early 1980s (Leahey, 1980, 1981, 1983, who was critical of the position, and Kendler, 1981, 1983, who defended it), and the early 1990s (Green, 1992; Koch, 1992, both of whom were very critical of operationism). Most recently, the journal
Theory and Psychologypublished a positive analysis of the development of operationism (Grace, 2001), followed by several critical commentaries (Bickhard, 2001; Green, 2001; Rogers, 2001).
ULJANAFEESTis a research scholar at the Max Planck Institute for the History of Science in Berlin, where she works on the historical relationship between Gestalt psychology and philosophy of science, and the epistemology of psychological experiments. She received a degree in psychology at the University of Frankfurt (Germany), and a Ph.D. at the Department of History and Philosophy of Science, University of Pittsburgh. This paper is based on parts of her dissertation, entitled “Operationism, Experimentation, and Concept Formation” (University of Pittsburgh, 2003).
Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002 /jhbs.20079 © 2005 Wiley Periodicals, Inc.
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The disagreements between advocates and critics of operationism appear to be largely of a philosophical nature. However, in discussing problems with operationism, proponents of this debate (in particular, critics of operationism) have made certain conceptualand historical as-sumptions—i.e., they have worked with particular notions of what the position of operationism states and what its historical origins were. In this article, I want to question some of these con-ceptual and historical assumptions. To this end, I will draw on case studies of two early opera-tionists, Stanley Smith Stevens (1906–1973) and Edward Chace Tolman (1886–1959). These case studies serve a dual purpose. On the one hand, I use them to provide a conceptual analy-sis of operationism, which is grounded in an analyanaly-sis of the role operationism played in the ex-perimental research of some of its early proponents. On the other hand, I use them to provide evidential support for my thesis that operationism was historically not as closely tied to certain other movements (most importantly, logical positivism) as is assumed by its critics.
ANALYZINGMETHODOLOGY IN THECONTEXT OFINVESTIGATIVEPRACTICE
Critics of operationism have proceeded by pointing out that operationism is fatally flawed, because it has its roots in—and/or is identical with—flawed philosophical positions (e.g., Green, 1992; Leahey, 1980, 1981, 1983; Rogers, 2001), or arises from misunderstandings of such posi-tions (Green, 1992; Koch, 1992). In this article, I will focus on the assumption that operationism is an expression of a logical positivist epistemology and a verificationist theory of meaning.1This
assumption is clearly behind the charge that psychologists have failed to notice that neither of those positions is still en voguewithin philosophy. Varieties of this critique have been formulated both by philosophers and by historians of psychology. For example, the philosopher Fred Suppe writes: “[I]t seems to be characteristic, but unfortunate, of science to continue holding philo-sophical positions, long after they are discredited” (Suppe, 1977, p. 19). In a similar vein, the his-torian Thomas Leahey states that “[p]sychologists . . . persisted (and still persist) in attempting to ‘define’ each theoretical term empirically even after the positivists had given it up for cognitively significant interpretive systems” (Leahey, 1980, pp. 132–133). Interestingly, however, the same historian also asserts that in actual scientific practice psychologists do not provide operational definitions, despite their claims to the contrary. Instead, he observes that “[t]he test maker must persuade the psychological community that his ‘definition’ . . . is a good one. . . . We find that operational definitions are not analytic truths, but are subject to empirical confirmation. This sug-gests that they are not ‘definitions’ at all” (Leahey, 1980, p. 138).
However, if psychologists do not, as a matter of fact, operationally define their terms along the model of an outmoded philosophical theory of knowledge and meaning (and I believe that Leahey is right about this), it is not so clear that a critique of those outmoded philosophical the-ories has much relevance to operationism as practiced by psychologists. Thus, we need an analy-sis of what the position really states, such that we can then delineate the grounds on which we want to attack, or defend, it. In this article, I aim to provide such an analysis of operationism, grounded in analyses of the scientific contexts that first gave rise to the emergence of this con-cept. By asking what function this concept played in the investigative practices of its proponents, I follow a trend in the historiography of psychology (e.g., Danziger, 1990) that does not take methodological writings at face value, but tries to gain an understanding of methodologies by asking how these methodologies were applied to, and emerged in the context of, specific
search questions. Some recent commentators on operationism share this focus on investigative practice (Rogers, 2001). However, while raising interesting questions about the emergence and longevity of operationism (see also Rogers, 1989), this author does not offer a detailed analysis of the position itself. Instead, he criticizes defenders of operationism for believing “that grand metatheoretic problems of the positivist project” can be solved by the introduction of a new method (Rogers, 2001, p. 61). The assumption here is that operationism has the very same metatheoretic foundations (and, hence, problems) as the positivist project. It should be empha-sized that not all critics of operationism assume that it was historically closely linked to logical positivism. For example, Green (1992) explicitly denies this. Yet, the suggestion that psychol-ogy would be better off if operationists had taken notice of the decline of logical positivism is a pervasive theme in the critical literature. I will now take a closer look at this suggestion.
TWONOTIONS OF“OPERATIONISM”
Roughly, we can distinguish between two theses that are frequently attributed to opera-tionism, an epistemologicalthesis and a semanticthesis. According to the epistemological the-sis, all knowledge claims have to be reducible to actual or potential observations (see Salmon, 1985). According to the semantic thesis, the meaning of a concept can be exhaustively defined by stating particular operations and their observational results. Both of these theses are com-monly associated with the philosophy of logical positivism. Therefore, I will dub this construal of operationism the “positivist” reading of operationism. In this section, I contrast this reading with my own “methodological” reading of operationism.
Operationism: The Methodological Reading
The thesis of this section is that psychological operationism was never intended as a the-ory of meaning or a thethe-ory of knowledge in the philosophical sense. By this, I mean that psy-chologists did not intend to say, generally, what constitutes the meaning of a scientific term. Nor did they intend to provide a general account of justification for scientific knowledge. This does not mean that semantic and epistemological questions were of no concern. Thus, I believe that in offering operational definitions, scientists were partially and temporarilyspecifying their usage of certain concepts by saying which kinds of empirical indicators they took to be indica-tive ofthe referents of the concepts.2For example, in his psychophysical work on attributes of
tonal experience, the operationist Stanley Smith Stevens started with the prior assumption that discriminatory behavior in response to auditory stimuli could be treated as indicative of audi-tory experience. This assumption is what was behind his “definition” of experience—i.e., that “to experienceis, for the purpose of science, to react discriminatively” (Stevens, 1935c, p. 521). Given, further, a certain methodology for prompting subjects to discriminate according to par-ticular featuresof their auditory experience, this prior assumption enabled Stevens to do empir-ical research on the “density” and “volume” of tones and to show how each of these attributes of experience vary as a function of particular physical stimuli. In a similar vein, in his research on problem-solving behavior in rats, the operationist Edward Chace Tolman, who believed that behavior was dependent on “cognitions” and “demands,” worked with a prior assumption, ac-cording to which the demand for a certain object varies relative to the degree with which the or-ganism has been deprived of that item, and that the vigorousness of searching behavior was, in turn, a function of this. Given these prior assumptions, Tolman took himself to be able to show experimentally how particular desires vary as a function of deprivation.
I will argue in the next section that these types of “definitions” did not have the status that philosophers usually associate with the term—i.e., they did not have the status of a priori knowl-edge or analytical truths. Rather, they were eithertemporary assumptions about typical empiri-cal indicators of a given subject matter, which allowed researchers to get empiriempiri-cal investigations “off the ground”, orthey were presentations of the outcomesof experiments, which were as-sumed to individuate a given phenomenon particularly well. Thus, on my construal, they had a
methodologicalfunction. Regarding the question of whether operationism was intended as an empiricist epistemology, it may be helpful to distinguish between two notions of epistemology. According to the first notion, the aim of epistemology is to provide a theory of what it would take to justify existing systems of knowledge. According to the second, the aim of epistemology is to formulate guidelines for the acquisition of new knowledge. This latter notion of epistemology may also be referred to as “methodology” (I take this distinction from Dingler, 1936/1988). While philosophers are traditionally interested in the former, it is a contention of this article that early psychological operationists, as practicing experimental scientists, were interested in the latter.
On the methodological reading suggested here, an investigation of operational definitions in psychology provides a framework for studying the process of concept formation in an ex-perimental context, or—to use the terminology of Hans-Jörg Rheinberger—of the coming into being of “epistemic things” (Rheinberger, 1997).
Operationism: The Positivist Reading
As is well known, the epistemological and semantic tenets of positivism were, for related reasons, soon recognized as problematic, and were subject to gradual changes and refinements until the 1960s (Carnap, 1936/1937; Hempel, 1950, 1952, 1954; Quine, 1951). In a nutshell, it was recognized that (a) there are statements, which scientists take to be justified, even though it is impossible to exhaustively rephrase them in terms of observation sentences, and (b) there are statements about objects, which we intuitively recognize as meaningful, despite the fact that the concepts that occur in those statements cannot be exhaustively defined in terms of operations and resulting observations. The epistemological recognition led to the insight that a theoretical sentence cannot be verified, but at best confirmed, by observations. This implies that the mean-ings of such statements cannot be reduced to methods of verification. Carnap realized this early on for statements containing disposition terms, stating that such terms can only partiallybe de-fined by observations (Carnap, 1936/1937), and later adding that many terms of a theory are im-plicitlydefined by their place in the theory (Carnap, 1956). In a similar vein, philosophers called into question the notion of explicit definitions as requiring necessary and sufficient conditions of application (Hempel, 1965). The recognition that observations can, at best, confirm scientific statements went hand-in-hand with the introduction of a dichotomy between theory- and obser-vation language, such that sentences in the latter could be used to confirm sentences in the for-mer. This dichotomy, however, was soon called into question by reference to the theory-laden-ness of observation (e.g., Hanson, 1958), and because it relied on the distinction between analytic and synthetic sentences, which was famously and radically attacked by Quine (1951).
With this simplified overview of the development of positivist philosophy in mind, we can now appreciate that critics of operationism attribute to this doctrine various views that were held (or are commonly thought to have been held) by philosophers of the positivist tra-dition.3First, there is the charge that operational definitions purport to provide necessary and
sufficient conditions of application. This, as was observed in the literature and reiterated by later critics, would lead to “an uncritical multiplication of concepts” (Leahey, 1981; Weber, 1940), and fly in the face of the scientific intuition that one and the same concept can apply in more than one situation, and that it can be applied even in the absence of an empirical con-dition of application (Hempel, 1954). Related to the worry about a multiplication of concepts is the charge that operationists are antirealists about the referents of their concepts—i.e., that one can arbitrarily introduce concepts regardless of whether they refer to something in the world (e.g., Leahey, 1983; Michell, 1999). Second, there is the charge that operationists buy into the analytic/synthetic distinction, believing statements that contain operational defini-tions to constitute a prioriknowledge and thereby be analytically true, in which case “there is nothing left to discover” (Green, 1992, p. 296), and any empirical evidence in support of a definition would be circular, thus robbing it of its explanatory value (Leahey, 1981).
OPERATIONISM INSCIENTIFICCONTEXT: THECASES OFSTEVENS ANDTOLMAN
In this section, I will elaborate on my case studies of Stevens’s and Tolman’s operationisms, showing that the positivist reading does not do justice to their operationisms. In the following sec-tion, this analysis will be complemented with brief historical outlines of how their operationisms originated and what was the nature of their contact with positivist philosophers of science.
Stevens’s Operational Treatment of Consciousness
Stanley Smith Stevens (1906–1973), who is mainly known for his work on psy-chophysics and measurement theory, arrived at Harvard for graduate studies in the fall of 1931. Less than two years later, he defended his dissertation on the perceived attributes of tones. His advisor was E. G. Boring (1886–1968). After a few more years—having worked as a researcher in various other departments at Harvard—he accepted an offer to become an in-structor of psychology. During the second half of the 1930s, he published his four papers on operationism (Stevens, 1935b, 1935c, 1936, 1939a). Since these papers are full of references to his psychophysical work on attributes of tones, I shall begin by outlining this work, as well as the way Stevens uses the notion of “definition” there.
delin-eated a unique pattern of responses to particular combinations of stimulus dimensions, which he treated as evidence for the existence of experienced tonal volume.
In what sense may Stevens be said to be offering definitions? I will begin by looking at his assertion that “to experience is, for the purpose of science, to react discriminately” (1935c, p. 521). Did he mean by this that the expression experiencehas the same meaning as discrimina-tive behavior? Did he mean that the presence of discriminative behavior is always a necessary and sufficient condition for the correct application of the term experience? Based on his re-search, I think that this is clearly not what he has in mind. Rather, Stevens presupposedthat ex-perience of tonal volume or density is phenomenal (and thereby, presumably, that the phenom-enal aspect is an integral part of the meaning of the term). The question, for him, is how to “get at” particular kindsof phenomenal experience in an experimental context. His assertion is that this can only be done via the behavior of the organism—i.e., that in an experiment, discrimina-tive behavior is a necessary condition for attributing conscious experience to an organism. Having devised an experiment that elicits such behavior in a regular fashion, he concluded, “[w]e are justified in saying that volume is a phenomenal dimension of tones” (1934a, p. 406). Now, what about the “definitions” of tonal density and volume that Stevens offered as a resultof his empirical investigation? While Stevens seemed to think that the criteria offered in his definition of tonal volume were sufficient conditions for the applicability of the term, I don’t believe that he took them to be necessaryconditions.4This point is related to the
ques-tion of whether he was an antirealist about the referent of the concept. I believe that the fact that he conducted research on the neurophysiological basis of the experience of tones (see Stevens & Davis, 1936, 1938) shows that he believed the concept of tonal volume to be phys-ically realized. This suggests that (a) he took the term consciousnessto be more than a logical construct or a useful fiction (i.e., that he was not an antirealist about its referent) and (b) he would have been open to the possibility that it might in principle be detectable in more than one way (i.e., that the operational definition he offered was not intended to state necessary con-ditions for the applicability of the term). The status of his “definition,” I would like to suggest, was that of an empirical finding that was taken to confirm the existence of a phenomenon. This leads us to our last question—i.e., whether Stevens took either of those two types of “defini-tions” to be a prioritrue or unrevisable. The answer, I believe, is quite explicit in his own writ-ings. He thought of definitions as factual statements that can be changed5:
[Definitions] take into account the state of factual knowledge at a given time. It is for good reason that the discovery of new related facts may make a revision of the criteria necessary so that we may include or exclude the new observation from the class denoted by the original definition. . . . No concept can be defined once and for all: every concept requires constant purging to keep it operationally healthy. (Stevens, 1935c, pp. 519, 527)
Tolman’s Operationalization of Desires
Edward Chace Tolman (1886–1959) went to graduate school in the joint department of philosophy and psychology at Harvard University, where he received his PhD in psychology in
1915. He taught at Northwestern University for three years and then assumed a position at the University of California at Berkeley in 1918, where he stayed for the rest of his life. In 1932, he published his book, Purposive Behavior in Animals and Men. In the second half of the 1930s, Tolman published three papers in which he outlined his operationism (Tolman, 1936/1958f, 1937, 1938/1958d). Tolman’s operationism has to be seen in the context of his re-search on problem-solving behavior in rats. As is well known, Tolman attributed to rats the ability to form mental maps of their environments. As is less well known, he also assumed that the rat’s behavior is influenced by an internal drive or demand, which is dependent on the state of biological need the rat is in at the time when the problem solving is required. Given that Tolman saw himself as a behaviorist, he recognized that it was problematic to posit the exis-tence of these two types of internal states (cognitive maps and drives), which he called “inter-vening variables.” His operationism was motivated by his desire to justify the practice of ma-nipulating the state of organismic need by providing evidence for the existence of these states. In his first explicit paper on operationism, Tolman (1936) characterized this position as as-serting the existence of a set of intervening variables, certain functions whereby these interven-ing variables are related to particular independent variables (external stimuli), and certain func-tions whereby these intervening variables are related to particular dependent variables (types of behavior).6While his presentation of his position is at times confused, I believe that, based on
his scientific work, the following rational reconstruction can be given: Intervening variables are posited internal entities or phenomena that are assumed to causally intervenebetween stimuli and outward behavior. As in the case of Stevens, we find, strictly speaking, two kinds of “defi-nitions” in the work of Tolman. To illustrate this, let us look at his papers, “An Operational Analysis of ‘Demand’” and “The Determiners of Behavior at a Choice Point” (Tolman, 1937, 1938/1958d). As mentioned above, Tolman started out with a general presupposition about de-mands—i.e., that they can be affected by depriving organisms of particular types of objects (e.g., the hunger demand can be affected by depriving an organism of food) and that this in turn has an impact on behavior. Based on this prior assumption, Tolman conducted what he called a “defining experiment,” as a result of which he offered a mathematical equation of how the in-tensity of food-searching behavior in rats varies as a function of food deprivation.
Once again, we may ask in what sense Tolman can be said to be offering definitions here. First, it seems highly unlikely that Tolman intended his general notion of “demand” (as in-volving some kind of behavior in response to particular kinds of stimuli) to be exhaustive of the meaning of the term in ordinary language. Just as Stevens did not deny the subjective ele-ment of conscious experience, so Tolman did not deny the subjective character of certain men-tal states (see also Tolman, 1958c, 1927/1958b), but rather denied that this subjective feel could serve as a basis for a privileged kind of data in psychology. Thus, as in Stevens’s case, the point of the definition was to get an empirical handle on a phenomenon. Furthermore, when opera-tionalizing hungerin his research, the point, frequently, was not to do research on hunger per se, but to get a grip on this variable, in order to be able to control for this variable when test-ing hypotheses pertaintest-ing to othervariables. For example, in his 1932 book (i.e., before the publication of his operationism papers), Tolman operationalizes hunger in terms of “time since last feeding.” This, then, enabled him to conduct experiments about the question of whether different kinds of food are equally attractive to rats, given the same level of hunger (see Tolman, 1932a, for many examples of this strategy). When Tolman (1937) later provided what he called a “defining experiment” for the notion of “hunger,” he was attempting to legitimate the scientific practice he was already engaged in.
We may now ask what he took the status of this defining experiment to be: Did it provide a definition in the sense of necessary and sufficient conditions of application? Did he take it to refer to a real entity or was he an antirealist? Did he take the definitions to be a prioritrue and unrevisable? With respect to the first two questions, the verdict is mixed. In Tolman’s writ-ings on operationism, we find statements to the effect that a theory is a complex mathematical function, the terms of which are useful fictions. This is also how Tolman has been interpreted by MacCorquodale and Meehl (1948). However, I believe that we see here a certain lip service paid to the philosophy of logical positivism, whose proponents he had met by that time (more about this below). In his earlier work, it is clear that Tolman believed intervening variables to be causally efficacious in the production of behavior. This suggests to me that he took them to be real and that there might, in principle, be more than one way to identify them (i.e., the “defining experiment” does not provide a necessary, but at best a sufficient condition of ap-plication; see also Amundsen, 1983, in support of my claim that Tolman was not an antirealist about the referents of his concepts). With respect to the last question, Tolman was less explicit than Stevens. However, if we look at his writings, we find statements like the following: “[This behavior] will be taken as empirical evidence for, and definition of, immanent expectancy” (Tolman, 1932a, p. 20). This suggests to me that for Tolman (as for Stevens), the line between definition and empirical fact was not cut in stone, and that his “definitions” were working as-sumptions, based on what was known so far.
SOMEHISTORICALORIGINS OFSTEVENS’S ANDTOLMAN’SOPERATIONISMS
In the previous section, I have shown that the “positivist” reading of operationism does not seem to fit the writings or practices of two operationists investigated here. In this section, I will complement these accounts with some aspects of the conditions that contributed to the emergence of these operationisms. The thesis of this section is that both Stevens’s and Tolman’s methodological views about operationism “co-evolved” with their scientific ideas and inves-tigative practices, which preceded their contact with logical positivists.
Stevens and the Psychophysical Tradition
An important factor toward the development of Stevens’s operationism was his advisor, Edwin Boring (1886–1968). Boring was important both in shaping Stevens’s understanding of the history of psychophysics (through his historical work, e.g., Boring, 1929) as well as his the-oretical and methodological views. With respect to the latter, Boring’s The Physical Dimensions of Consciousness(1933) is especially important. About this book, Boring later wrote, “[t]ucked away in my little book was this basic faith in operationism” (Boring, 1952, p. 44).7Stevens was
closely involved in the production of the book.8This book served the dual purpose of
articulat-ing a physicalist methodology for psychology and attemptarticulat-ing to develop a modern-day variety of Wundt and Titchener’s project of investigating elements of consciousness. Let us take a brief look at both of these aspects (for a more detailed account, see Feest, 2002).
7. In this context, Boring also mentions that this “basic faith” in operationism goes back at least to his paper “The Stimulus-Error,” published in 1921. Boring’s 1923 paper, “Intelligence as the Test Tests It,” should also be men-tioned. Both of these articles precede Stevens’s operationism by more than a decade. A detailed historical inves-tigation of the relationship between those earlier papers by Boring is needed to assess Boring’s own claims about the matter.
Boring’s book had the aim of rejecting psychophysical dualism in its ontological and
methodological variety. Ontologically, I believe we can attribute to Boring some kind of mind/brain identity theory. By asserting the existence of conscious experience, but stating that it is identical with brain states, he distanced himself from both traditional substance dualism and from behaviorism. Here, I will focus on the methodologicalaspect.9Boring wanted to
re-ject the notion that psychology required a different methodology from other sciences. In argu-ing this, he distanced himself from Titchener’s introspectivism (see Borargu-ing, 1929). Borargu-ing’s 1933 book was, in part, an attempt to reject Titchener’s methodological dualism and replace it with a single, physicalist conception of scientific method. “Historically science is physical sci-ence. Psychology, if it is to be a science, must be like physics” (Boring, 1933, p. 6). For Boring, this meant that experience was a theoretical entity, to be inferred on the basis of behavior: “There is no way of getting at ‘direct experience,’ because experience gives itself up to science indirectly, inferentially, by the experimental method” (Boring, 1933, p. 6). Two years later, Stevens used a very similar formulation in arguing for his view that if “experience” was to be a scientific concept, it had to be amenable to the operational procedure, rather than being ac-cessed by some more “immediate,” introspective means: “Operationism requires that we deal only with the reportable aspects of experience. Operational psychology knows precisely noth-ing of unreported consciousness” (Stevens, 1935b, p. 327).
Having talked about the origins of Stevens’s methodologicalcommitments, let us now look at the origins of his theoreticalcommitments. Here, I believe we can make out two strands. On the one hand, Stevens’s research was in the psychophysical tradition, going back to Fechner’s at-tempts to measure experience as a function of physical stimuli (Fechner, 1860).10Stevens saw
himself as carrying forth this research, while explicating quite clearly the underlying assump-tions about empirical indicators of conscious experience. This need for explication was, I be-lieve, prompted by the heightened methodological awareness of the problematic status of con-sciousness as an object of scientific study in the aftermath of behaviorist critiques. The other strand, once again, takes us back to Boring’s book of 1933, Dimensions of Consciousness. It was an explicit goal of this book to further develop Titchener’s notion of dimensions of conscious-ness, albeit stripped of Titchener’s dualism: “My book was a move away from Titchener, but it also served to make his dimensionalism clear” (Boring, 1961, p. 53). What Boring was refer-ring to in the latter part of the sentence here was Titchener’s structuralism—i.e., the project of studying the mind by dissecting it into its basic parts (Boring, 1933, also referred to this project as “mental chemistry”). Given the focus of early experimental psychology on the study of sen-sation, it is not surprising that there was some psychological debate about sensations as basic el-ements of the mind (see Boring, 1933, 1942). According to Boring (and cited by Stevens), sci-entific interest in attributesof sensation goes back to Wilhelm Wundt (1893, Chapter 10), who characterized sensation in terms of attributes (quality and intensity), without, however, giving a systematic account of this analysis.11Külpe (1893) gave a more systematic treatment of
attrib-utes, distinguishing between quality, intensity, and duration (for all senses), and adding exten-sionfor the senses of vision and touch. In addition, there were attempts to introduce mental
el-9. Stevens rejected Boring’s idea that substance dualism could be disproved on scientific grounds. In his private note-book of early 1933, he mentions a discussion he and Boring had about this (HUG (FP)-2.45, Box 1).
10. More recent predecessors dealing specifically with auditory experience were Helmholtz (1863) and Stumpf (1883,1890).
ements other than sensations.12The Titchenerian tradition of American psychology later ruled
out images and feelings as basic elements of consciousness, thereby equating consciousness with sensation (for a more detailed account, see Boring, 1933). The structuralist focus on sen-sations as basic elements of consciousness came under attack with the rise of Gestalt psychol-ogy. Boring attributed to Titchener a theoretical response to this state of affairs, which, however, Titchener never fully worked out. According to this view, consciousness is to be described in terms of four basic dimensions (quality, intensity, extensity, and protensity; see Titchener, 1929), with each sense modality having different attributes that can be classified under these dimen-sions.13It was this idea that Boring wanted to argue for in his 1933 book.
Unfortunately, Boring’s book was a flop and only sold 105 copies in the first 17 years (cf. Boring, 1961, p. 53). According to Stevens, this lack of success was, in part, due to the fact that Boring had not been able to provide experimental evidence for his claim that conscious ex-perience has certain attributes, or dimensions. At that point in time, Stevens’s work on tonal at-tributes, which would have demonstrated this point, had not yet been completed: “[S]ome of the research that [Boring] was directing [i.e., Stevens’s own research] was soon to clarify the relation between tonal sensation and its four attributes: pitch, loudness, volume, and density” (Stevens, 1968, p. 597). The relevance of Stevens’s research on tonal attributes to Boring’s work on dimensions of consciousness can also be gathered from the fact that Boring made this work a central point of reference in his 1935 article “Attributes of Sensation” (Boring, 1935). The relevance of Stevens’s operationism to his experimental work on tonal attributes, in turn, can be inferred from the fact that Stevens devoted a whole section of his paper “The Operational Definition of Psychological Concepts” (Stevens, 1935c) to the discussion of tonal attributes. Thus, my thesis is that the emergence of Stevens’s operationism was closely related to his psychophysical work on tonal attributes, which in turn raised methodological issues about how to conceptualize and measure such attributes.
Tolman’s Notions of Instincts and Instrumental Reasoning
Important cues as to the origins and enabling conditions for Tolman’s operationism can be found in the nature of the intervening variables that he proposed (i.e., “demands” and “cogni-tions”). In this section, I argue that (a) attempts to get a scientific grip on “demand” concepts go back to the mid-1920s and can be traced back even farther to his student days, and (b) his answer as to how to investigate (i.e., operationalize) the referents of such concepts is closely related to his notion of “cognition,” which also had an interesting development within his thought.14
Within Tolman’s work, we find reference to bothof these variables (albeit under different names) as early as 1925 (e.g., Tolman, 1925/1958h). Tolman believed that any given action is always going to be determined by both of these types of intervening variables, where the for-mer provides the motivating force for a behavior and the latter enables the organism to repre-sent knowledge about the world. Tolman needed to conceptualize these notions such that they could be experimentally teased apart (e.g., by holding one constant and observing the effect on the other, which obviously required some prior assumptions as to what are typical causes and effects of such internal states). Equally important, however, he needed to come up with some behavioristically respectable account of why it was permissible to appeal to such “mentalistic”
12. For example, Külpe tried to find elements of (imageless) thought, and Titchener argued that there were three classes of mental elements: sensations, images, and feelings (Titchener, 1910).
13. The distinction between dimensions and attributes is not completely clear. Boring admits that “[t]he dimensions of consciousness are the immediate successors to the old attributes of sensation” (Boring, 1933, p. 23).
notions at all. This is particularly apparent in his writings about demands. This question, for him, had two aspects: (1) what criteria could be used when describinga behavior as purposive (this was related to his notion of “molar” behavior) and (2) on what grounds might it be per-missible to explain a behavior by appeal to an internal motivating state (see Tolman, 1925/1958a; 1926). In his development of how he dealt with these questions, it is important to recognize the impact of McDougall’s notion of instinct. In fact, I believe that Tolman’s think-ing about demands has to be viewed as an attempt to put McDougall’s notion of “instinct” on an objective, behavioral footing. Tolman had first come across McDougall’s work in a seminar he took with one of his Harvard professors, Ralph Barton Perry (1876–1957), while he was a graduate student there (Tolman, 1952). Perry’s own attempts to develop a scientific notion of “value” are also significant here (see Perry, 1926). In his articles leading up to this work (Perry, 1918, 1921a, 1921b, to which Tolman, 1920, 1922, appealed), Perry explicitly endorsed both a doctrine of behaviorism and the notion that behavior has to be scientifically explained by ap-peal to beliefs and desires. Lastly, one of Tolman’s other Harvard mentors, Edwin B. Holt (1873–1946), has to be mentioned, who—among other things—focused on the issue of how it is possible to describe purposive behavior in objective (nonteleological) terms (1915).15
Tolman thought of demands as providing the drives that motivate biological organisms to engage in instrumental reasoning. His notion of “cognition,” thus, was one of instrumental rea-soning. According to Tolman’s theory of purposive behavior, environmental features are cog-nitively represented in terms of how they can be used or manipulated in order to attain certain goals.Or, to use Tolman’s own terminology, environmental features are represented as “means-objects,” which figure in “cognitive postulations” (or hypotheses) as to what would happen if the object were to be manipulated in a certain way(Tolman, 1932a). Thus, for Tolman, cogni-tive representations are always formed relacogni-tive to certain goals(e.g., the goal to get to the food) and they involve expectations as to the outcomes of hypothetical actions(e.g., “if I were to take the left lane, this would get me to the food”). I believe that we can make out a variety of fac-tors that may have enabled Tolman to move toward this view.
One such factor was Robert Yerkes’s (1876–1956) research on primate intelligence. In 1916, Yerkes published a monograph, The Mental Life of Monkeys and Apes, based on research carried out in the spring of 1915, in which he reported several experiments that he conducted with orang-utans, which (while quite ambiguous) he took to demonstrate their capacity for instrumental rea-soning. It is known that Tolman took a class on comparative psychology with Yerkes at Harvard around 1915.16 Another important intellectual stimulation was German Gestalt psychology.
During his early career, Tolman undertook two visits to Germany (one after his first year of grad-uate school, in 1911, and one in 1923), where he stayed with Kurt Koffka, though each of these stays was only brief.17In his later work, Tolman emphasized the importance of Kurt Lewin’s
no-tion of objects having a certain “valence” (see Tolman, 1952, but see also Tolman, 1932a, 1932b), but also his notion of molar behavior as being more than the sum of physiological processes, as well as his usage of the expression sign-gestalts, indicates his closeness to certain Gestalt psy-chological ideas, though he took this latter notion to be broader than theirs, in that it emphasized the relationship between perception and action. For example, a chair might be mentally repre-sented as “that chair, if placed against the wall, can be stood upon like a stepladder to reach this
15. See Feest (in press) for a more detailed account of the impact of Perry and Holt on Tolman, and a discussion of how Tolman’s treatment of drives was located in the instinct debate of the 1920s.
16. It may also be speculated that Wolfgang Köhler’s research on primate intelligence, conducted on Tenerife around the same time, may have had an indirect impact on Tolman, as Köhler and Yerkes were corresponding (Ash, 1995; Kohler, 1917).
picture” (Tolman, 1933/1958e, p. 80). Two other important figures to be mentioned here are Egon Brunswik (1903–1955) and David Krech (1909–1977). Tolman met Brunswik while on sabbati-cal in Vienna in 1933/1934 (after the publication of his Purposive Behavior, but before the pub-lication of his papers on operationism), and they published a paper together (Tolman & Brunswik, 1935). According to Tolman’s own account, Brunswik “gave me new insight into the essentially achievement character of behavior” (Tolman, 1952). Apart from significant differ-ences between the two, it seems to me that Brunswik’s impact consisted of underscoring an el-ement that was already present in Tolman’s thinking—i.e., the notion that all behavior is based on hypotheses about the nature of the environment, which may or may not be correct. The major new insight that Tolman picked up here (which had, of course, been implied by his previous work) was the notion that all knowledge is fallible. Tolman recognized that this idea was simi-lar to his own notion that behavior is guided by sign-gestalts. Since sign-gestalts were essen-tially hypotheses about the outcomes of hypothetical manipulations, there was always a chance that they might notlead to the desired outcomes (i.e., that they were mistaken). In their joint publication, Tolman and Brunswik spelled out these basic ideas in more detail, essentially stat-ing that both with respect to perception as well as action, the organism faces a degree of uncer-tainty, which the organism copes with by trying to come up with hypotheses that maximize the probability of success. The notion that sign-gestalts are hypotheseshad already begun to appear in the context of Tolman’s experimental work shortly before his encounter with Brunswik. In particular, it was tied to work that he conducted with his student Isodore Krechevsky (Krechevsky, 1932a, 1932b; Tolman & Krechevsky, 1933).18This (and more) work was later
summarized in Tolman’s article on cognitive maps in rats (Tolman, 1948).
With this overview, I hope to have given some plausibility to my thesis that Tolman’s op-erationism was an attempt to legitimate his talk about intervening variables, and that his views on how to conceptualize these variables went back to his student days. Furthermore, I think that his views about cognitive representations in rats (conceived as hypotheses as to what would happen if the object in question were manipulated) were similar to his own practice of opera-tionalizing concepts—i.e., as referring to hypothetically posited objects, which, if experimen-tally manipulated in a certain way, are expected to behave a certain way (thereby confirming hypotheses about the existence of such objects).
The Impact of Positivism
The above outlines of the origins of Stevens’s and Tolman’s operatonisms are not intended to be exhaustive. For example, I have neglected to mention a variety of factors that may have contributed to my main actors’ intellectual development.19Furthermore, by pointing to the
con-texts in which certain methodologies originatedI have not thereby provided an analysis of why they were adopted. For example, while claiming that the basic tenets of these two varieties of operationism were similar, I have only hinted at possible explanations for whythese positions ended up looking so similar (namely, by reference to the methodological distrust of traditional introspectivism and mentalism, which both of these scientists had adopted from behaviorism), despite the very different origins and research interests of their proponents.
While my historical outlines were supposed to show (among other things) that these opera-tionisms were already being contemplated before the scientists in question encountered
sentatives of logical positivism, this is not to deny that both Stevens and Tolman did indeed en-counter representatives of logical positivism, and that this had an impact on how they formulated their operationisms. I believe that those references were largely rhetorical, aimed at backing up their views by appealing to cutting-edge philosophy of science. Let us begin with Stevens. Herbert Feigl, a member of the Vienna Circle, was at Harvard in 1930, but this was before Stevens’s time. While it has been asserted that Feigl brought Bridgman’s operationism to the at-tention of Harvard psychologists (see Green, 1992; Moyer, 1991), this is contradicted by Boring’s own retrospective account, according to which both he and Stevens were unaware of Bridgman’s operationism when they were working on the Consciousnessbook (Boring, 1961). At any rate, if Feigl (via Boring) left any traces in Stevens’s thinking, this is not reflected in Stevens’s early note-books of 1932 and 1933. Hardcastle (1995) has made the case that Stevens’s knowledge of German was limited and that he was therefore unlikely to have been exposed to logical positivism before Carnap’s 1934 contribution to the journal Philosophy of Science(Carnap, 1934). However, by the mid- to late 1930s, Stevens did know positivist philosophers of science, got involved with the Unity of Sciencemovement in the late 1930s, and explicitly related his operationism to this movement in his 1936 paper.20But this strikes me as an ex postadoption of terminology, rather
than reflecting a genuine impact on the content of his own operationism.
With respect to Tolman, I would like to make a similar point. As I showed in the case study, the essential components of Tolman’s operationism were already implicit in his writ-ings from at least the mid-1920s onward. The remaining question is what prompted him to articulate this position as an explicit doctrine in the mid- and late 1930s. An obvious answer, which Tolman confirmed in his 1937 paper, is that in the 1930s he came across S. S. Stevens’s and Bridgman’s formulations of operationism. Another obvious suggestion is that while in Vienna, Tolman got acquainted with members of the Vienna circle, and possibly read Carnap’s “Psychology in Physical Language” (Carnap, 1932). There is good reason to believe that Tolman attended meetings of the Vienna Circle, based on his friendship with Brunswik, as well as the fact that Schlick had been a visitor at the Philosophy Department at Berkeley a couple of years earlier. Also, Tolman was approached to present a paper at the 1936 Unity of Sciencecongress, but was unable to attend (the paper he had planned to pres-ent was his 1937 paper on operationism). However, I would like to make the case that he was only adopting a label for a position that was already fairly consolidated and that differed from the kind of position that is usually associated with positivism.
EPISTEMOLOGICALPROBLEMS WITHOPERATIONISM
The aim of my historical case studies was to argue that operationism in psychology was not identical with, nor was it significantly influenced by, an empiricist epistemology or a ver-ificationist theory of meaning. According to this analysis, both scientists in question wanted to legitimate their research on “mentalistic” topics by providing empirical criteria of application for their concepts.21These empirical criteria of application were “definitions” insofar as they
specified features that these authors took to be indicative of their purported subject matter— thereby enabling them to do research on that subject matter—but they were not intended to ex-haustively provide the meanings of the concepts in question, or to be unrevisable. However,
20. Stevens presented a paper, entitled “On the Problem of Scales for the Measurement of Psychological Attitudes,” at the Fifth International Congress for the Unity of Science, which was held at Harvard University in September 1939 (see Stadler, 1997, p. 431).
while my analysis may imply that psychological operationism cannot have inherited the spe-cific problems of empiricism and verificationism, it does not imply that it does not have prob-lems of its own. The problem I want to discuss here is that of circularity.
The issue is that it would be circular to justify the validity of a concept by reference to the operations that led to its introduction.22This was one of the problems that
behav-iorists had made out in traditional mentalism. As argued above, operationism was, in part, an attempt to deal with this problem. So, if operationism cannot avoid circularity (as has been suggested by critics), it would have failed to meet this goal (this problem is also pointed out by Green, 1992, p. 300). One possible way of avoiding circularity would be to provide evidence for a given thing (e.g., Stevens’s tonal density and volume or Tolman’s demand) by showing that it can be detected by different means(i.e., different experimen-tal operations). If I am correct in my contention that both Stevens and Tolman were real-ists about the referents of their concepts, then it is plausible to assume that they would have believed this to be permissible. Indeed, by the mid-1940s, this was explicitly allowed by proponents of operationism (Boring, 1945). But none of the early operationists were able to provide criteria that would settle how to determine that two operations do indeed
“get at” the same object (i.e., operationalize the same concept). I believe that part of the appeal of operationism was its cautionary aspect, in that it advised scientists not simply to assume that one and the same concept applies under very different circumstances (i.e., when different operations are used).23
A related problem is that—given the assumption that the cognitive system is very com-plex, and given all the assumptions that go into an experimental setup—one may be skeptical of whether a particular experiment really individuates any onecognitive process in pure, un-contaminated form (or at all, for that matter). In other words, did Tolman really have grounds for assuming that his “defining experiments” on demands, even if such a cognitive entity re-ally exists, acture-ally reflected demands, rather than being the output of a complex interaction of any number of cognitive processes that are required when the rat performs in a maze? As described by Grace (2001), both of these problems were addressed by subsequent method-ological developments within psychology. On the one hand, the convergent/discriminant op-erations (or multitrait-multimethod) approach suggested correlating the results of different tests of the same purported phenomenon, and of similar tests about different purported phe-nomena (Campbell & Fiske, 1959). On the other hand, the converging operations approach suggested designing experiments that would specifically test alternative hypotheses to ac-count for the data (Garner et al., 1956).
I do not intend to go into the details of these methods or whether they successfully deal with the problems just outlined, let alone whether psychologists today can generally be said to apply them correctly. Rather, the point of this section was to isolate what I take to be a problem that critics of operationism might legitimately be concerned about. However, as mentioned earlier, in response to Grace’s article, several authors suggested that there is something deeply wrong with operationism, which cannot be fixed by superficial
method-22. By the notion of validity, psychologists mean that a concept or test refers to what it is thought to refer to. This is different from the notion of validity in logic.
ological innovations. In the following section, I will discuss the questions of what this de-bate might be about.
WHATIS THEDEBATEABOUT—WHATSHOULDITBEABOUT?
Let us start with the charge that operationism—contrary to its own assertions—is not metaphysically neutral (Bickhard, 2001; Green, 1992, p. 314). I believe that this charge is di-rected at the positivist rejection of metaphysics, and the idea of a neutral observation language. Once again, it might be helpful to keep in mind the difference between the positivist and the operationist project. Positivists attempted to formulate an epistemology that was metaphysi-cally neutral (e.g., Carnap, 1931). Operationists (on my construal) attempted to formulate a methodology for an empirical psychology, which was sensitive to problems with introspec-tivism and mentalism, and which forced psychologists to explicate their prior assumptions about how to interpret observations. Kendler (1981) also emphasizes this point when he argues that when there is a disagreement between empirical psychologists about a given phenomenon, it may turn out that the disagreement is not about the empirical results, but about how to oper-ationalize the concept.
Let us turn to a second, related critique of operationism—that it implies a particular no-tion of what it means to be scientific, which in turn has an impact on how psychological phe-nomena are conceptualized and what kinds of psychological phephe-nomena can be scientifically investigated at all. According to this critique, the charge is not merely that operationism is not metaphysically neutral, but that it promotes a particularmetaphysical picture. One version of this charge is that operationism is intricately tied to quantitative and experimental methods— i.e., an understanding of psychology as a natural science. For example, Leahey (1983) argues that a naturalistically conceived psychology (which operationism—according to him—stands for) cannot account for the phenomenon of intentionality. What I take him to be saying here is that operationism is incapable of employing qualitative or hermeneutic methods, which would do more justice to the psychological subject matter. The first of these two assertions does not strike me as self-evidently true, but it certainly warrants further discussion. More importantly, though, I would like to argue that operationism is not committed to any particular notion of the subject matter of psychology. While it is true that Stevens and Tolman (as we have seen) were indeed proponents of a quantitative and experimental method in psychology, I believe that this coincidence is historically contingent. To put it quite bluntly, all empirical psychologists have to operationalize their concepts.And all empirical psychologists have to argue for their results by laying open both their conceptual presuppositions and their empirical data. Viewed this way, the issue seems to be whether psychology can be an empirical science at all.
One last critique of operationism is that psychologists frequently confuse definitions and facts—i.e., they think that operational definitions can substitute for theoretical work about the referent of the concept. In this vein, Christopher Green quite appropriately points out that “al-though operational definitions might have a role to play in piloting nascent “al-thought about a given phenomenon, they cannot ultimately replace the fruits of hard, rigorous thought” (Green, 1992, p. 315). While agreeing with this assessment, I believe that he is expressing a critique of certain widespread research practices, not of operationism per se.24
Summing up this section, I believe the debate mistakenly focuses on the tenability of op-erationism, where in fact it should be about the question of preconditions for psychology as an empirical science and about the question of whether psychologists exhibit the requisite thoughtfulness in their research. Insofar as there is agreement that psychology can be an em-pirical science, the debate should then be about what are adequate concepts and how (not whether) to operationalize them, and how (not whether) to validate them. This task is far from trivial, and it may turn out that the gaps between different (e.g., qualitative vs. quantitative) ap-proaches within psychology cannot be bridged. However, I believe that the gap, ultimately, is not one between proponents and opponents of operationism.
CONCLUSION
In this article, I have provided a conceptual analysis of the notion of operationism in psychology. This analysis was based on a historical investigation of the operationisms of two early proponents, S. S. Stevens and E. C. Tolman. Two construals of operationism were introduced, a “positivist” and a “methodological” reading. It was argued that while critics of operationism frequently assume a positivist reading of this position, an analysis of the ways in which operationism was applied in Stevens’s and Tolman’s research suggests a methodological reading, according to which operational definitions have a pragmatic role to play in psychological research, but are not taken to be necessarily true or unrevisable. This analysis was further backed up by a historical study of the origins of both Stevens’s and Tolman’s operationisms, which revealed that neither one of them had any significant contact with proponents of positivism in philosophy, until the substance of their position was already in place. I then presented an analysis of some epistemological problems with operationism, and the ways in which methodological writings in the 1950s tried to address these problems. Lastly, I claimed that the current debate about operationism is really about a couple of deeper points of contention, and I suggested that these should be addressed in-dependently of the issue of operationism.
ACKNOWLEDGMENTS
I would like to thank Bob Olby who first encouraged me to pursue this project in a graduate class I took with him in 1998. I also thank the members of my dissertation com-mittee, especially my advisor, Peter Machamer, and my friend Stephanie Koerner. Thanks to audiences at the 2003 ESHHS-meeting and at the Max Planck Institute for the History of Science as well as to two anonymous referees for helpful remarks. I am grateful to Nancy Innis for sharing information about Tolman with me. Last but not least, many thanks to Ray Fancher and to the members of the Wiley production department.
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