The “theory” approach to concepts, one of three that Machery endorses in Doing without Concepts (2009), reflects a widespread view in psychology that is typically taken to be promising but in need of further development (e.g., Carey Reference Carey1985; Gopnik & Meltzoff Reference Gopnik and Meltzoff1997). According to this approach, concepts constitute or are embedded within intuitive theories about the world. However, both philosophers and psychologists have been quick to point out that the notion of an intuitive theory is underspecified, and that appeals to scientific theories run the risk of substituting one mystery for another (Laurence & Margolis Reference Laurence, Margolis, Margolis and Laurence1999). Machery is aware of these concerns, but he identifies the locus of the theory view's commitments not in the notion of an intuitive theory or in appeals to scientific theory, but in explanation. For an advocate of the theory approach, concepts store “knowledge that can explain the properties of the category members,” so “much hangs on the notion of explanation” (Machery Reference Machery2009, p. 101).
Machery is right to focus on the central role of explanation for theory-based approaches to concepts. In a set of influential papers that kick-started theory theorizing, theories were defined as “any of a host of mental explanations” (Murphy & Medin Reference Murphy and Medin1985, p. 290) and characterized in terms of “laws and other explanatory mechanisms” (Carey Reference Carey1985, p. 201). Categorization and category learning were described as “special cases of inference to the best explanation” (Rips Reference Rips, Vosniadou and Ortony1989, p. 53), with a concept invoked “when it has a sufficient explanatory relation to an object” (Murphy & Medin Reference Murphy and Medin1985, p. 295). But such appeals to explanation were not proposed against a backdrop of psychological theories of explanation. Rather, they predominantly appealed to what Machery calls a “folk understanding of explanation” (2009, p. 102), contributing to the concern that theory-based approaches to concepts are underspecified.
What to do? One option would be to develop psychological theories of explanation, with our folk understanding as a guide. A second option would be to ground psychologists' appeals to explanation in philosophical theories of scientific explanation. Given the analogy between science and cognition that motivates many proponents of the theory approach, this seems like a natural move. But it is not the one Machery advocates. In fact, Machery cautions that “philosophical accounts of scientific explanation would probably be useless for spelling out the psychological notion of theory” (2009, p. 102).
I want to suggest that Machery is wrong to dismiss the psychological value of theories of explanation from the philosophy of science and to neglect recent advances that move the psychology of explanation beyond “folk understanding.” Scientists are, after all, psychological creatures, and there is every reason to expect the aspects of human cognition that shape everyday explanations to play a role in science. Scientists and everyday cognizers also face similar problems and have similar goals: They confront limited data, and from this they must construct a representation of the world that supports relevant predictions and interventions.
But there is another reason to expect a close correspondence between philosophical and psychological accounts of explanation, one that stems from the philosophical methods typically employed. Here, in uncharitable caricature, is how theory development often proceeds: Philosopher P1 proposes theory T1 of explanation; philosopher P2 quickly generates putative counterexample C, a specific case in which T1 makes one prediction about what is explanatory, but philosopher P2's intuition demurs. The philosophical community pronounces one way or the other, based largely on shared intuitions about C, so T1 stands (for now) or gives way to a new theory. This is not the most efficient way to collect data, and it would not pass muster for an experimental psychologist; but to the extent philosophers are like everyday folk, one would expect convergence between philosophical theories and descriptively adequate accounts of everyday intuitions.
In fact, a growing body of experimental work suggests that theories of explanation from philosophy can usefully inform the psychology of explanation and bear a close correspondence to everyday judgments (for reviews, see Keil Reference Keil2006; Lombrozo Reference Lombrozo2006). While there is no consensus on a theory of explanation in philosophy, different strands of theorizing seem to capture different aspects of the psychology of explanation. For example, some studies on the role of explanation in category learning have drawn on subsumption and unification accounts of explanation (e.g., Williams & Lombrozo, in press), while others on categorization and inference are consistent with causal theories (e.g., Rehder Reference Rehder2003b; Reference Rehder2006). Empirical research on the cognitive significance and consequences of different kinds of explanations – specifically, functional versus mechanistic explanations (Kelemen Reference Kelemen1999; Lombrozo Reference Lombrozo2009; under review; Lombrozo & Carey Reference Lombrozo and Carey2006; Lombrozo et al. Reference Lombrozo, Kelemen and Zaitchik2007) – has its roots in Aristotle, but can trace a path to contemporary philosophers such as Daniel Dennett.
One reason to appreciate this richer, philosophically informed psychology of explanation is because it has implications for Machery's heterogeneity hypothesis. In particular, the two distinct summary representations that Machery recognizes – theories and prototypes – can be understood as embodying different kinds of (potentially) explanatory structure. Machery recognizes this point, and in fact rejects philosophical accounts of explanation, such as Salmon's statistical relevance model, in part because allowing statistical relationships to play a role in explanation would “blur the distinction” between theories and prototypes (Machery Reference Machery2009, p. 102). But perhaps the fact that explanations are sensitive to causal and statistical relationships is a reason to endorse such accounts. Evidence suggests that explanations are sensitive to multiple kinds of knowledge – about causal structure and functional relationships (Lombrozo & Carey Reference Lombrozo and Carey2006), about statistical regularities (Hilton & Slugoski Reference Hilton and Slugoski1986), and about principled generic knowledge (Prasada & Dillingham Reference Prasada and Dillingham2006). These are precisely the kinds of knowledge that Machery suggests concepts contain.
Recognizing the “heterogeneity” of explanatory structure does not eliminate the heterogeneity of concepts, but it does suggest a path to unifying concepts by appeal to explanation. It also pushes back Machery's concerns about natural kinds and elimination from concepts to explanation: What are the distinct kinds of explanatory relations, and do they as a class support relevant generalizations that suggest “explanation” is a natural kind and a valuable theoretical term for a mature psychology? Perhaps these are the questions we should be asking.
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The “theory” approach to concepts, one of three that Machery endorses in Doing without Concepts (2009), reflects a widespread view in psychology that is typically taken to be promising but in need of further development (e.g., Carey Reference Carey1985; Gopnik & Meltzoff Reference Gopnik and Meltzoff1997). According to this approach, concepts constitute or are embedded within intuitive theories about the world. However, both philosophers and psychologists have been quick to point out that the notion of an intuitive theory is underspecified, and that appeals to scientific theories run the risk of substituting one mystery for another (Laurence & Margolis Reference Laurence, Margolis, Margolis and Laurence1999). Machery is aware of these concerns, but he identifies the locus of the theory view's commitments not in the notion of an intuitive theory or in appeals to scientific theory, but in explanation. For an advocate of the theory approach, concepts store “knowledge that can explain the properties of the category members,” so “much hangs on the notion of explanation” (Machery Reference Machery2009, p. 101).
Machery is right to focus on the central role of explanation for theory-based approaches to concepts. In a set of influential papers that kick-started theory theorizing, theories were defined as “any of a host of mental explanations” (Murphy & Medin Reference Murphy and Medin1985, p. 290) and characterized in terms of “laws and other explanatory mechanisms” (Carey Reference Carey1985, p. 201). Categorization and category learning were described as “special cases of inference to the best explanation” (Rips Reference Rips, Vosniadou and Ortony1989, p. 53), with a concept invoked “when it has a sufficient explanatory relation to an object” (Murphy & Medin Reference Murphy and Medin1985, p. 295). But such appeals to explanation were not proposed against a backdrop of psychological theories of explanation. Rather, they predominantly appealed to what Machery calls a “folk understanding of explanation” (2009, p. 102), contributing to the concern that theory-based approaches to concepts are underspecified.
What to do? One option would be to develop psychological theories of explanation, with our folk understanding as a guide. A second option would be to ground psychologists' appeals to explanation in philosophical theories of scientific explanation. Given the analogy between science and cognition that motivates many proponents of the theory approach, this seems like a natural move. But it is not the one Machery advocates. In fact, Machery cautions that “philosophical accounts of scientific explanation would probably be useless for spelling out the psychological notion of theory” (2009, p. 102).
I want to suggest that Machery is wrong to dismiss the psychological value of theories of explanation from the philosophy of science and to neglect recent advances that move the psychology of explanation beyond “folk understanding.” Scientists are, after all, psychological creatures, and there is every reason to expect the aspects of human cognition that shape everyday explanations to play a role in science. Scientists and everyday cognizers also face similar problems and have similar goals: They confront limited data, and from this they must construct a representation of the world that supports relevant predictions and interventions.
But there is another reason to expect a close correspondence between philosophical and psychological accounts of explanation, one that stems from the philosophical methods typically employed. Here, in uncharitable caricature, is how theory development often proceeds: Philosopher P1 proposes theory T1 of explanation; philosopher P2 quickly generates putative counterexample C, a specific case in which T1 makes one prediction about what is explanatory, but philosopher P2's intuition demurs. The philosophical community pronounces one way or the other, based largely on shared intuitions about C, so T1 stands (for now) or gives way to a new theory. This is not the most efficient way to collect data, and it would not pass muster for an experimental psychologist; but to the extent philosophers are like everyday folk, one would expect convergence between philosophical theories and descriptively adequate accounts of everyday intuitions.
In fact, a growing body of experimental work suggests that theories of explanation from philosophy can usefully inform the psychology of explanation and bear a close correspondence to everyday judgments (for reviews, see Keil Reference Keil2006; Lombrozo Reference Lombrozo2006). While there is no consensus on a theory of explanation in philosophy, different strands of theorizing seem to capture different aspects of the psychology of explanation. For example, some studies on the role of explanation in category learning have drawn on subsumption and unification accounts of explanation (e.g., Williams & Lombrozo, in press), while others on categorization and inference are consistent with causal theories (e.g., Rehder Reference Rehder2003b; Reference Rehder2006). Empirical research on the cognitive significance and consequences of different kinds of explanations – specifically, functional versus mechanistic explanations (Kelemen Reference Kelemen1999; Lombrozo Reference Lombrozo2009; under review; Lombrozo & Carey Reference Lombrozo and Carey2006; Lombrozo et al. Reference Lombrozo, Kelemen and Zaitchik2007) – has its roots in Aristotle, but can trace a path to contemporary philosophers such as Daniel Dennett.
One reason to appreciate this richer, philosophically informed psychology of explanation is because it has implications for Machery's heterogeneity hypothesis. In particular, the two distinct summary representations that Machery recognizes – theories and prototypes – can be understood as embodying different kinds of (potentially) explanatory structure. Machery recognizes this point, and in fact rejects philosophical accounts of explanation, such as Salmon's statistical relevance model, in part because allowing statistical relationships to play a role in explanation would “blur the distinction” between theories and prototypes (Machery Reference Machery2009, p. 102). But perhaps the fact that explanations are sensitive to causal and statistical relationships is a reason to endorse such accounts. Evidence suggests that explanations are sensitive to multiple kinds of knowledge – about causal structure and functional relationships (Lombrozo & Carey Reference Lombrozo and Carey2006), about statistical regularities (Hilton & Slugoski Reference Hilton and Slugoski1986), and about principled generic knowledge (Prasada & Dillingham Reference Prasada and Dillingham2006). These are precisely the kinds of knowledge that Machery suggests concepts contain.
Recognizing the “heterogeneity” of explanatory structure does not eliminate the heterogeneity of concepts, but it does suggest a path to unifying concepts by appeal to explanation. It also pushes back Machery's concerns about natural kinds and elimination from concepts to explanation: What are the distinct kinds of explanatory relations, and do they as a class support relevant generalizations that suggest “explanation” is a natural kind and a valuable theoretical term for a mature psychology? Perhaps these are the questions we should be asking.