Unlike my attack on Quine’s argument for natural kinds realism, my problems with Kripke’s natural kinds realism did make it into my dissertaion. My focus there wasn’t on natural kinds; it was, instead, on Kripke’s general theory of non-connotativity of certain terms (and natural kind terms are among them). But, at least for Kripke, non-connotativity of natural kind terms and natural kinds realism are closely tied, so the same argument will do for both. For those of you who aren’t terribly excited about the idea of looking up my dissertation, I’ll put a somewhat abridged version of my argument here.
Kripke’s Original Argument
Kripke’s argument for natural kinds realism is, essentially, this: We don’t specify, through anything like definition, the extensions of our natural kind terms. For example (his example), there’s no set of concepts associated with the term “tiger” that uniquely picks out all and only tigers. Indeed, tigers could turn out to have none of the attributes associated with our concepts of them. Although they, for example, appear to eat meat, be related to cats, and be striped, these could (though it’s exceptionally implausible–it’s not impossible, and that’s all he needs) turn out to have none of these attributes. The apparent relation to cats could be a result of our inadequate understanding of genetics, the stripedness could be an optical illusion, and the meat-eating could in fact be something very different (perhaps–remember, we’re allowing the implausible here–tigers’ claws convert the creatures they kill into 100% textured tofu, so they never consume an iota of meat).
(Kripke has another argument, about water, that goes in the other direction–that something can have all the properties we conceptually associate with a kind without being a member of the kind. I’ll cover that in a separate post.)
How do natural kind terms get their extensions? Well, Kripke wants to present, as opposed to a conceptual model, a causal model. The initial referent of “tiger” (or, more likely, some linguistic ancestor of “tiger”) was a tiger because of something that Kripke called a “baptismal event”–generally an ostention (“I shall call that thing [pointing] a tiger”) but possibly an *initial* description (“I shall call the creature that mauled this water buffalo a tiger”). At any rate, in all likielihood, this baptismal event picked out only a single object, or possibly a small number of objects. The relationship of that term to other tigers is that other tigers are part of the same natural kind. The extent of that natural kind is a scientific fact to be discovered, not a definitional one to be stipulated. And the relationship of our term “tiger” to tigers is that there’s the right sort of “causal chain” between the initial term’s usage and our current usage of “tiger.”