In Doing without Concepts (Machery Reference Machery2009; hereafter DwC), Machery proposes that heterogeneity in the mental representation of “concepts” is sufficient to render that term useless. As he argues, the term can refer to exemplars, prototypes, and theories. However, it can also refer to defaults (Connolly et al., Fodor et al. Reference Connolly, Fodor, Gleitman and Gleitman2007), aspects (Prasada & Dillingham Reference Prasada and Dillingham2009), Boolean concepts (Feldman Reference Feldman2000; Goodwin & Johnson-Laird Reference Goodwin and Johnson-Laird2010; submitted; Shepard et al. Reference Shepard, Hovland and Jenkins1961), and connections yet to be discovered. Thus, in our view, Machery's taxonomy is too narrow, and it underestimates the degree of heterogeneity that exists in the representation of concepts. It excludes a variety of conceptual phenomena that do not fall within the purview of prototypes, exemplars, and theories. We turn next to describe two examples of such conceptual phenomena – Boolean concepts, and connections expressed by generics.
Boolean concepts – those that are composed out of negation (not), disjunction (or), and conjunction (and) – are an important kind of everyday concept. They occur frequently in the form of laws, rules, or procedures. Indeed, Machery's criteria for individuating concepts are themselves Boolean concepts (see sect. 2 of Machery's Précis of DwC in this issue). A concept does not need to be entirely Boolean in order for it to contain relevant Boolean structure, however. How individuals learn Boolean concepts is still not resolved, but many of the current leading contenders are not based on exemplars, prototypes, or theories (Feldman Reference Feldman2006; Vigo Reference Vigo2009). We have recently proposed an alternative theory, based on mental models, which analyzes the complexity of concepts in terms of the number of distinct possibilities that a concept can be compressed into (Goodwin & Johnson-Laird, submitted). This theory predicts the acquisition of Boolean concepts as well as, if not better than, the other leading contenders, and it too is not based on the representational mechanisms that Machery assumes to be exhaustive in explaining conceptual knowledge.
Recently, we published a paper documenting the occurrence of “conceptual illusions,” in which people think that particular instances of a Boolean concept are possible when in fact they are not, and vice versa (Goodwin & Johnson-Laird Reference Goodwin and Johnson-Laird2010). A typical example is the concept: green and large, or else green, in a context in which all possible objects are either green or not, and either large or small (the “or else” here represents exclusive disjunction). A large percentage of individuals think that an object that is both green and large is possible given this description, which is in fact erroneous. The exclusive disjunction between the two clauses means that the only possible object is one that is both green and small. This error, as well as others like it, is predicted by the mental model theory's principle of conceptual truth. And as far as we can tell, accounts based on prototypes, exemplars, or theories have no way to explain these errors.
Other examples of conceptual phenomena unaccounted for by the taxonomy described in DwC include the connections and relations that link concepts together. Such connections can be concepts unto themselves, and are revealed by generic assertions such as “tigers are striped,” “barns are red,” or “ticks carry Lyme disease,” which express generalizations about kinds of things (Carlson & Pelletier Reference Carlson and Pelletier1995; Gelman Reference Gelman2003; Lawler Reference Lawler1973). All three assertions are true for different reasons, and as such, generics provide a means for studying the types of connections we represent between concepts of kinds and properties. We have found that for statements such as “tigers are striped,” the relation between the kind (“tigers”) and the predicate (“are striped”) can be distinguished from logical, statistical, and causal connections (Khemlani et al., submitted; Prasada et al., submitted). These distinctions could account for phenomena in concept learning and conceptual development without importing any assumptions made by other theories of concepts. Thus, by studying generics, it is possible to discover the conceptual structure of generalizations without assuming the representational structure of the concepts to which they refer. Machery proposes that future research should examine differences between generics, and particularly how they differ from quantified assertions (DwC, p. 200), and we agree wholeheartedly. Unfortunately, the proposals in DwC do not leave room to explore such advances in conceptual organization, as they encourage researchers to couch their work as falling within the domain of three fundamental classes of conceptual representation.
We do not think these phenomena, which point to even greater heterogeneity in the mental representation of concepts than Machery suggests, strengthen Machery's eliminativist argument to do away with concepts. The elimination of the term “concept” in favor of greater specificity tacitly endorses the assumption that prototypes, exemplars, and theories (and whatever else), are all that comprise concepts. It thus presupposes that contingent facts about the mental representation of concepts are the sole criterion for deciding whether “concept” ought to be preserved. But this presupposition ignores the common function that diverse sorts of concept play in representing knowledge and in communication. Concepts represent and convey systematic bodies of information, and they would retain this function regardless of how they are mentally represented. In other words, we think that the question of what counts as a concept needs answering at the computational level, not at the algorithmic one (cf. Marr Reference Marr1982).
Thus, Machery's eliminativist argument is too powerful. It gives no grounds for thinking that the term “concept” is in an especially precarious position. In much the same way that the term organizes a wide array of “memory.” Would Machery have us do away with these terms as well, given heterogeneity in the cognitive processes to which they refer? Perhaps, but we think this is going too far.
In sum, the key functions of concepts are to represent and communicate knowledge, and this general functional property is what argues in favor of preserving the term “concept.” We believe that heterogeneity at the level of mental representation is no obstacle to the further empirical investigation of concepts.
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In Doing without Concepts (Machery Reference Machery2009; hereafter DwC), Machery proposes that heterogeneity in the mental representation of “concepts” is sufficient to render that term useless. As he argues, the term can refer to exemplars, prototypes, and theories. However, it can also refer to defaults (Connolly et al., Fodor et al. Reference Connolly, Fodor, Gleitman and Gleitman2007), aspects (Prasada & Dillingham Reference Prasada and Dillingham2009), Boolean concepts (Feldman Reference Feldman2000; Goodwin & Johnson-Laird Reference Goodwin and Johnson-Laird2010; submitted; Shepard et al. Reference Shepard, Hovland and Jenkins1961), and connections yet to be discovered. Thus, in our view, Machery's taxonomy is too narrow, and it underestimates the degree of heterogeneity that exists in the representation of concepts. It excludes a variety of conceptual phenomena that do not fall within the purview of prototypes, exemplars, and theories. We turn next to describe two examples of such conceptual phenomena – Boolean concepts, and connections expressed by generics.
Boolean concepts – those that are composed out of negation (not), disjunction (or), and conjunction (and) – are an important kind of everyday concept. They occur frequently in the form of laws, rules, or procedures. Indeed, Machery's criteria for individuating concepts are themselves Boolean concepts (see sect. 2 of Machery's Précis of DwC in this issue). A concept does not need to be entirely Boolean in order for it to contain relevant Boolean structure, however. How individuals learn Boolean concepts is still not resolved, but many of the current leading contenders are not based on exemplars, prototypes, or theories (Feldman Reference Feldman2006; Vigo Reference Vigo2009). We have recently proposed an alternative theory, based on mental models, which analyzes the complexity of concepts in terms of the number of distinct possibilities that a concept can be compressed into (Goodwin & Johnson-Laird, submitted). This theory predicts the acquisition of Boolean concepts as well as, if not better than, the other leading contenders, and it too is not based on the representational mechanisms that Machery assumes to be exhaustive in explaining conceptual knowledge.
Recently, we published a paper documenting the occurrence of “conceptual illusions,” in which people think that particular instances of a Boolean concept are possible when in fact they are not, and vice versa (Goodwin & Johnson-Laird Reference Goodwin and Johnson-Laird2010). A typical example is the concept: green and large, or else green, in a context in which all possible objects are either green or not, and either large or small (the “or else” here represents exclusive disjunction). A large percentage of individuals think that an object that is both green and large is possible given this description, which is in fact erroneous. The exclusive disjunction between the two clauses means that the only possible object is one that is both green and small. This error, as well as others like it, is predicted by the mental model theory's principle of conceptual truth. And as far as we can tell, accounts based on prototypes, exemplars, or theories have no way to explain these errors.
Other examples of conceptual phenomena unaccounted for by the taxonomy described in DwC include the connections and relations that link concepts together. Such connections can be concepts unto themselves, and are revealed by generic assertions such as “tigers are striped,” “barns are red,” or “ticks carry Lyme disease,” which express generalizations about kinds of things (Carlson & Pelletier Reference Carlson and Pelletier1995; Gelman Reference Gelman2003; Lawler Reference Lawler1973). All three assertions are true for different reasons, and as such, generics provide a means for studying the types of connections we represent between concepts of kinds and properties. We have found that for statements such as “tigers are striped,” the relation between the kind (“tigers”) and the predicate (“are striped”) can be distinguished from logical, statistical, and causal connections (Khemlani et al., submitted; Prasada et al., submitted). These distinctions could account for phenomena in concept learning and conceptual development without importing any assumptions made by other theories of concepts. Thus, by studying generics, it is possible to discover the conceptual structure of generalizations without assuming the representational structure of the concepts to which they refer. Machery proposes that future research should examine differences between generics, and particularly how they differ from quantified assertions (DwC, p. 200), and we agree wholeheartedly. Unfortunately, the proposals in DwC do not leave room to explore such advances in conceptual organization, as they encourage researchers to couch their work as falling within the domain of three fundamental classes of conceptual representation.
We do not think these phenomena, which point to even greater heterogeneity in the mental representation of concepts than Machery suggests, strengthen Machery's eliminativist argument to do away with concepts. The elimination of the term “concept” in favor of greater specificity tacitly endorses the assumption that prototypes, exemplars, and theories (and whatever else), are all that comprise concepts. It thus presupposes that contingent facts about the mental representation of concepts are the sole criterion for deciding whether “concept” ought to be preserved. But this presupposition ignores the common function that diverse sorts of concept play in representing knowledge and in communication. Concepts represent and convey systematic bodies of information, and they would retain this function regardless of how they are mentally represented. In other words, we think that the question of what counts as a concept needs answering at the computational level, not at the algorithmic one (cf. Marr Reference Marr1982).
Thus, Machery's eliminativist argument is too powerful. It gives no grounds for thinking that the term “concept” is in an especially precarious position. In much the same way that the term organizes a wide array of “memory.” Would Machery have us do away with these terms as well, given heterogeneity in the cognitive processes to which they refer? Perhaps, but we think this is going too far.
In sum, the key functions of concepts are to represent and communicate knowledge, and this general functional property is what argues in favor of preserving the term “concept.” We believe that heterogeneity at the level of mental representation is no obstacle to the further empirical investigation of concepts.