This paper was originally published in E. Margolis & S. Laurence (eds.) Concepts: Core Readings, Cambridge, Mass.: MIT Press. Chapter 1 Concepts and Cognitive Science Stephen Laurence and Eric Margolis 1. Introduction: Some Preliminaries Concepts are the most fundamental constructs in theories of the mind. Given their importance to all aspects of cognition, it's no surprise that concepts raise so many controversies in philosophy and cognitive science. These range from the relatively local Should concepts be thought of as bundles of features, or do they embody mental theories? to the most global Are concepts mental representations, or might they be abstract entities? Indeed, it's even controversial whether concepts are objects, as opposed to cognitive or behavioral abilities of some sort. Because of the scope of the issues at stake, it's inevitable that some disputes arise from radically different views of what a theory of concepts ought to achieve-differences that can be especially pronounced across disciplinary boundaries. Yet in spite of these differences, there has been a significant amount of interdisciplinary interaction among theorists working on concepts. In this respect, the theory of concepts is one of the great success stories of cognitive science. Psychologists and linguists have borrowed freely from philosophers in developing detailed empirical theories of concepts, drawing inspiration from Wittgenstein's dis- cussions of family resemblance, Frege's distinction between sense and reference, and Kripke's and Putnam's discussions of externalism and essentialism. And philosophers have found psychologists' work on categorization to have powerful implications for a wide range of philosophical debates. The philosopher Stephen Stich (1993) has gone so far as to remark that current empirical models in psychology undermine a tradi- tional approach to philosophy in which philosophers engage in conceptual analyses. As a consequence of this work, Stich and others have come to believe that philoso- phers have to rethink their approach to topics in areas as diverse as the philosophy of mind and ethics. So even if disciplinary boundaries have generated the appearance of disjoint research, it's hard to deny that significant interaction has taken place. We hope this volume will underscore some of these achievements and open the way for increased cooperation. In this introduction, we sketch the recent history of theories of concepts. However, our purpose isn't solely one of exposition. We also provide a number of reinterpretations of what have come to be standard arguments in the field and develop a framework that lends more prominence to neglected areas This paper was fully collaborative; the order of the authors' names is arbitrary. 4 Laurence and Margolis of the intellectual geography. Given the vast range of theories at play, it would be impossible to say anything substantive without offending some theoretical scruples. So we should say right now that we don't claim to be completely neutral. As we go along, we try to justify our choices to some extent, but inevitably, in a space as short as this, certain views will receive less attention. Our strategy is to present what we take to be the main theories of concepts and do this in terms of idealized character- izations that provide rather rough yet useful demarcations. Before we begin, however, there are three preliminary issues that need to be men- tioned. Two can be dealt with fairly quickly, but the third-concerning the onto- logical status of concepts-requires a more extended treatment. Primitive, Complex and Lexical Concepts' For a variety of reasons, most discussions of concepts have centered around lexical concepts. Lexical concepts are concepts like BACHELOR, BIRD, and BITE-roughly, ones 2 that correspond to lexical items in natural languages. One reason for the interest in lexical concepts is that it's common to think that words in natural languages inherit their meanings from the concepts they are used to express. In some discussions, con- cepts are taken to be just those mental representations that are expressed by words in natural languages. However, this usage is awkward, since it prohibits labeling as concepts those representations that are expressed by complex natural language expressions. One wouldn't be able to say, for example, that the concept BLACK CAT (corresponding to the English expression "black cat") is composed of the simpler concepts BLACK and CAT; only the latter would be concepts. Yet most of the reasons that one would have to single out BLACK and CAT and the like as concepts apply equally to complexes that have these as their constituents. There may be little differ- ence between lexical concepts and other complex concepts apart from the fact that the former are lexicalized; indeed, on many views, lexical concepts are themselves complex representations. At the same time, it seems wrong to designate as con- cepts mental representations of any size whatsoever. Representations at the level of complete thoughts-that is, ones that may express whole propositions-are too big to be concepts. Accordingly, we will take concepts to be subpropositional mental representations. Two other points of terminology should be mentioned. We'll say that primitive concepts are ones that lack structure. Complex concepts, in contrast, are concepts that aren't primitive. In the cognitive science literature, primitive concepts are sometimes called atomic concepts or features, although this terminology is confused by the fact that "feature" is sometimes used more permissively (i.e., to refer to any component of a concept) and is sometimes used more restrictively (i.e., to refer to only primitive sensory concepts). We'll adopt a permissive use of "feature" and say that unstruc- 1. Throughout, we will refer to concepts by using expressions in small caps. When quoting, we will adjust other people's notations to our own. 2. For present purposes, there is no need to insist on a more precise characterization, apart from noting that the concepts in question are ones that are usually encoded by single morphemes. In particular, we won't worry about the possibility that one language may use a phrase where another uses a word, and we won't worry about exactly what a word is (but for some alternative conceptions, see Di Sciullo and Williams 1987). Admittedly, the notion of a lexical concept isn't all that sharp, but it does help to orient the discussion toward the specific concepts that have been most actively subjected to investigation, for instance, BIRD as opposed to BIRDS THAT EAT REDDISH WORMS IN THE EARLY MORNING HOURS. Concepts and Cognitive Science 5 Lured concepts are primitive or atomic. What exactly it means to say that a concept has, or lacks, structure is another matter. This brings us to our second preliminary point. Two Models of Conceptual Structure Most theories of concepts treat lexical concepts as structured complexes. This raises the issue of what it is for such representational complexes to have structure. Despite the important role that conceptual structure plays in many debates, there has been little explicit discussion of this question. We discern two importantly different models of structure that are implicit in these debates. The first view we'll call the Containment Model. On this view, one concept is a structured complex of other concepts just in case it literally has those other concepts as proper parts. In this way, a concept C might be composed of the concepts X, Y, and Z. Then an occurrence of C would necessarily involve an occurrence of X, Y, and Z; because X, Y, and Z are contained within C, C couldn't be tokened without X, Y, and Z being tokened. For example, the concept DROPPED THE ACCORDION couldn't be tokened without ACCORDION being tokened. As an analogy, you might think of the relation that words bear to phrases and sentences. The word "accordion" is a structural element of the sentence "Tony dropped the accordion" in the sense that it is a proper part of the sentence. Consequently, you can't utter a token of the sen- tence "Tony dropped the accordion" without thereby uttering a token of the word "accordion." The second view, which we'll can the Inferential Model, is rather different. Accord- ing to this view, one concept is a structured complex of other concepts just in case it stands in a privileged relation to these other concepts, generally, by way of some type of inferential disposition. On this model, even though X, Y, and Z may be part of the structure of C, C can still occur without necessitating their occurrence. For example, RED might have a structure implicating the concept COLOR, but on the Inferential Model, one could entertain the concept RED without having to token the concept COLOR. At most, one would have to have certain dispositions linking RED and COLOR-for example, the disposition to infer X Is COLORED from X IS RED. Thus, for any claim that a concept has such-and-such structure-or such-and-such type of structure (see sec. 7)-there will be, in principle, two possible interpretations of the claim: one in terms of the Containment Model and one in terms of the Inferen- tial Model. The significance of these distinctions will become clearer once we present some specific theories of concepts. For now we simply want to note that discussions of conceptual structure are often based on an implicit commitment to one of these models and that a proper evaluation of a theory of concepts may turn on which model is adopted. Concepts as Abstracta vs. Concepts as Mental Representations The third and last preliminary point that we need to discuss concerns a more basic issue-the ontological status of concepts. In accordance with virtually all discussions of concepts in psychology, we will assume that concepts are mental particulars.