A widespread assumption in the literature on concepts is that concepts form a unified, or singular, natural kind, as opposed to a set of different natural kinds. That is, advocates of different accounts disagree on which kind of thing constitutes concepts, but they agree that there is only one such kind of thing (with different instances for each category).
In recent years, two young philosophers,
Dan Weiskopf and
Edouard Machery, have completed Ph.D. dissertations questioning this assumption, independently of each other. Dan graduated from Washington University in St. Louis roughly at the time I went there for my PNP postdoc (2003). I met him and learned about his work.
In the fall 2004, I co-taught a course on concepts with Sam Scott, who at the time was the other Wash U PNP postdoc. Sam did some ground-breaking empirical work on non-referring concepts, so he knows a lot more than I did about the psychological literature on concepts.
I wanted to learn more about Dan’s work and discuss it in class, so I asked Dan for a copy of his
paper in progress, which is now available on his website. Unfortunately, the paper may not have been ready at the time. At any rate, he didn’t send it to me. But during the course, Sam and I discovered Edouard’s paper,
Concepts Are Not a Natural Kind, which at the time was forthcoming in Philosophy of Science (it is now published).
Since we didn’t have Dan’s paper, we decided to read and discuss Edouard’s paper instead. We were not entirely satisfied with Edouard’s argument, but we liked the conclusion—concepts split into different natural kinds—and we thought we could find better arguments. So we wrote a paper of our own.
Our paper, entitled “
Splitting Concepts”, is now officially forthcoming in Philosophy of Science.
In our paper, the argument I most care about is what we call the “argument from language”. Its conclusion is that there are at least two different kinds of concept, which may be called linguistic concepts (those that explain linguistic abilities) and non-linguistic concepts (those that explain cognitive abilities we have in common with non-linguistic animals and babies). I think this conclusion may have some appealing philosophical payoff:
Many philosophers like to point out that there are dramatic cognitive differences between linguistic and non-linguistic creatures. Language seems to carry with it a lot of cognitive power. If you combine this observation with the two common assumptions that linguistic abilities are explained by concepts and that concepts are a singular natural kind, you face a dilemma. Either non-linguistic animals and babies have concepts or they don’t. If they do, you should explain why they are not as smart as we are even though they have concepts. If they don’t, you should explain why they are as smart as they are even though they have no concepts. Either way, you need a different theory of cognition for non-linguistic animals and babies as you do for linguistically competent human beings. Needless to say, philosophers have explored both options, but I’ve never been satisfied with either of them. Alternatively, you could try to downplay the cognitive differences between linguistic and non-linguistic creatures, but that doesn't sound very appealing either. Now there is a better way out: reject the assumption that concepts are a singular natural kind. Animals and babies have one kind of conceptual mental representations. Then, babies develop a new kind of conceptual representation—linguistic representations. Once linguistic representations are in place, humans are well on their way to surpassing the intelligence and inferential power of other animal species.
Of course, this is little more than a slogan at this point. Perhaps some day it will turn into a theory.