We concur with Machery's broad assessment in Doing without Concepts (Machery Reference Machery2009) that the science of concepts has revealed matters to be rather a mess. But we strongly disagree with what Machery takes as the philosophical upshot of that messiness, as expressed in his book's title: that psychologists should scrub “concept” from their lexicon. First, the hybrid option is still live, and if concepts are hybrids, they may well be natural kinds. Second, even if “concept” fails to pick out a natural kind, it may yet be scientifically useful, even on Machery's own terms.
Machery correctly observes that hybrid theorists owe an account of when two bodies of knowledge are parts of the same concept. He proposes that psychologists are committed to the principle that they are genuine parts only if they are coordinated (Machery Reference Machery2009, p. 64), that is, if they generate consistent evaluations of cases. But he adduces some evidence that coordination often fails across parts of putative hybrids: for example, one representation says tomatoes are vegetables; a bit later, the other says they are not (p. 72).
But this coordination condition is too strong, as it would break up bodies of knowledge that psychologists treat as conceptual wholes, namely, sets of exemplars. Contextual shifts, such as those that adjust the perspective of the subject (e.g., from artist to biologist), can, within selective-retrieval models, shift which exemplar is retrieved, even when both exemplars are stored as being about the same thing – and thereby can shift, for particular cases, whether they will be counted as in the target category (see Braisby Reference Braisby, Forbus, Getner and Regier2005). Sets of similarly stored exemplars would thus fail Machery's coordination condition – forcing their dissolution, likely down to individual exemplars. But that's not how psychologists treat such exemplars. His argument against hybrids proves too much.
That the coordination condition is too strong does not remove the need for hybrid theorists to provide an account of conceptual wholes. Here is one proposal, building on machinery used much earlier in Machery's book, when he attempts to distinguish conceptual from background knowledge (pp. 11–12). There, he suggests that a body of knowledge about x is in the concept of x just in case it is “preferentially available when we think, reason, and so on, about x” (p. 11). There is nothing unique to a hybrid that keeps its fans from saying such things about its subconceptual parts. A hybrid theorist could therefore propose that two coreferential representations are parts of the same concept of x just in case each is preferentially available in such a way when we think, reason, and so on, about x. (We note that Machery's account of conceptualization may require some technical tweak for Frege cases; we expect that whatever would do that for his account, would also work for this proposal.) But a failure of coordination is irrelevant to this weaker condition.
Whether this proposal succeeds is an open question, and that is sufficient for our purposes here in contending that hybrids are still a live option. For, if “concepts” picks out hybrids, psychology should probably keep the term, as there will likely be informative generalizations to be made. As Machery argues, empirical research suggests that for most categories we have a prototype, a body of exemplars, and a theory, but not a definition. So, a hybrid theorist would be able to theorize that most concepts partially consist of a prototype, and so on, but not a definition. But we cannot read such generalizations off of Machery's reference-fixing description (p. 12); they are discoveries. So, if concepts are hybrids, “concept” probably picks out a class that supports many informative, useful generalizations.
Even if the above is incorrect about hybrids, “concept” would still have important work to do. As Machery suggests, scientists should keep a term if it plays a useful role (p. 239). “Concept” does that, by efficiently marking out a class that scientists want to make claims or ask questions about, even if it should turn that there are vanishingly few generalizations to be made about something merely in virtue of its being a concept. There are many terms in good scientific standing across various disciplines that play such roles, including, we would suggest, “algorithm,” “sub-atomic particle,” or “nutrient” (and even some specific nutrients, such as “vitamin B”; see Elder Reference Elder1994, p. 259.) None of these categories seems to support many generalizations about their members qua members, yet each is very useful in organizing established knowledge and continuing inquiry in their respective domains. And the same holds for “concept.” For example, the neo-empiricist, friendly to Machery's general take on our conceptual systems, might want to defend the substantive claim that perceptual symbols are a kind of concept. Such a claim would be substantive, to the effect that the delineated class contains some additional sorts of entities. Indeed, Machery himself wonders whether there are other kinds of concepts (p. 249). For example, he writes, “Evidence shows that people have some knowledge about ideals. What is now needed is to determine whether these bodies of knowledge qualify as concepts” (p. 249). This strikes us as a meaningful and important question, and one for which the term “concept” is obviously useful in asking.
So, independent of the question of hybrids, psychologists should keep the term. Even if Machery is right, and concepts are not a natural kind, the potential dangers here would be better addressed through reformation instead of elimination. The practical advice to take away from Machery's arguments may be, not that scientists should get rid of “concept,” but that they should be more careful in understanding that this term likely fails to pick out a very tidy sort of natural kind. Doing so should allow them to steer around the sorts of dangers that Machery (Reference Machery2009) hypothesizes about (e.g., pp. 242–243), without sinking an otherwise fruitful vehicle of inquiry. The psychology of categorization, inference, and so on may be much messier than philosophers and psychologists have hoped. But “concept” is still likely to be a vitally important word for theorizing about that mess.
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We concur with Machery's broad assessment in Doing without Concepts (Machery Reference Machery2009) that the science of concepts has revealed matters to be rather a mess. But we strongly disagree with what Machery takes as the philosophical upshot of that messiness, as expressed in his book's title: that psychologists should scrub “concept” from their lexicon. First, the hybrid option is still live, and if concepts are hybrids, they may well be natural kinds. Second, even if “concept” fails to pick out a natural kind, it may yet be scientifically useful, even on Machery's own terms.
Machery correctly observes that hybrid theorists owe an account of when two bodies of knowledge are parts of the same concept. He proposes that psychologists are committed to the principle that they are genuine parts only if they are coordinated (Machery Reference Machery2009, p. 64), that is, if they generate consistent evaluations of cases. But he adduces some evidence that coordination often fails across parts of putative hybrids: for example, one representation says tomatoes are vegetables; a bit later, the other says they are not (p. 72).
But this coordination condition is too strong, as it would break up bodies of knowledge that psychologists treat as conceptual wholes, namely, sets of exemplars. Contextual shifts, such as those that adjust the perspective of the subject (e.g., from artist to biologist), can, within selective-retrieval models, shift which exemplar is retrieved, even when both exemplars are stored as being about the same thing – and thereby can shift, for particular cases, whether they will be counted as in the target category (see Braisby Reference Braisby, Forbus, Getner and Regier2005). Sets of similarly stored exemplars would thus fail Machery's coordination condition – forcing their dissolution, likely down to individual exemplars. But that's not how psychologists treat such exemplars. His argument against hybrids proves too much.
That the coordination condition is too strong does not remove the need for hybrid theorists to provide an account of conceptual wholes. Here is one proposal, building on machinery used much earlier in Machery's book, when he attempts to distinguish conceptual from background knowledge (pp. 11–12). There, he suggests that a body of knowledge about x is in the concept of x just in case it is “preferentially available when we think, reason, and so on, about x” (p. 11). There is nothing unique to a hybrid that keeps its fans from saying such things about its subconceptual parts. A hybrid theorist could therefore propose that two coreferential representations are parts of the same concept of x just in case each is preferentially available in such a way when we think, reason, and so on, about x. (We note that Machery's account of conceptualization may require some technical tweak for Frege cases; we expect that whatever would do that for his account, would also work for this proposal.) But a failure of coordination is irrelevant to this weaker condition.
Whether this proposal succeeds is an open question, and that is sufficient for our purposes here in contending that hybrids are still a live option. For, if “concepts” picks out hybrids, psychology should probably keep the term, as there will likely be informative generalizations to be made. As Machery argues, empirical research suggests that for most categories we have a prototype, a body of exemplars, and a theory, but not a definition. So, a hybrid theorist would be able to theorize that most concepts partially consist of a prototype, and so on, but not a definition. But we cannot read such generalizations off of Machery's reference-fixing description (p. 12); they are discoveries. So, if concepts are hybrids, “concept” probably picks out a class that supports many informative, useful generalizations.
Even if the above is incorrect about hybrids, “concept” would still have important work to do. As Machery suggests, scientists should keep a term if it plays a useful role (p. 239). “Concept” does that, by efficiently marking out a class that scientists want to make claims or ask questions about, even if it should turn that there are vanishingly few generalizations to be made about something merely in virtue of its being a concept. There are many terms in good scientific standing across various disciplines that play such roles, including, we would suggest, “algorithm,” “sub-atomic particle,” or “nutrient” (and even some specific nutrients, such as “vitamin B”; see Elder Reference Elder1994, p. 259.) None of these categories seems to support many generalizations about their members qua members, yet each is very useful in organizing established knowledge and continuing inquiry in their respective domains. And the same holds for “concept.” For example, the neo-empiricist, friendly to Machery's general take on our conceptual systems, might want to defend the substantive claim that perceptual symbols are a kind of concept. Such a claim would be substantive, to the effect that the delineated class contains some additional sorts of entities. Indeed, Machery himself wonders whether there are other kinds of concepts (p. 249). For example, he writes, “Evidence shows that people have some knowledge about ideals. What is now needed is to determine whether these bodies of knowledge qualify as concepts” (p. 249). This strikes us as a meaningful and important question, and one for which the term “concept” is obviously useful in asking.
So, independent of the question of hybrids, psychologists should keep the term. Even if Machery is right, and concepts are not a natural kind, the potential dangers here would be better addressed through reformation instead of elimination. The practical advice to take away from Machery's arguments may be, not that scientists should get rid of “concept,” but that they should be more careful in understanding that this term likely fails to pick out a very tidy sort of natural kind. Doing so should allow them to steer around the sorts of dangers that Machery (Reference Machery2009) hypothesizes about (e.g., pp. 242–243), without sinking an otherwise fruitful vehicle of inquiry. The psychology of categorization, inference, and so on may be much messier than philosophers and psychologists have hoped. But “concept” is still likely to be a vitally important word for theorizing about that mess.