Published online by Cambridge University Press: 05 June 2012
Saul Kripke, Naming and Necessity, 2nd edn (Oxford: Blackwell, 1980), lecture III; and H. Putnam, ‘Meaning and Reference’, Journal of Philosophy, 70 (1973), pp. 699–711.
Saul Kripke's arguments against description theories of names inaugurated a revolution in the philosophy of language. One of the first acts of that revolution was an application of similar arguments against a similarly descriptive theory of another sort of expression – so-called natural-kind terms. Kripke himself claimed that natural-kind terms are rigid designators. In this he was supported by the semi-independent work of Hilary Putnam. Kripke and Putnam together are acknowledged as the creators of a new theory of such terms. This chapter focuses on the work by these two philosophers in which they first proposed that new theory.
But what are natural-kind terms? They differ from proper names in this: whereas proper names pick out individuals, natural-kind terms pick out kinds. Favourite examples are ‘tiger’ and ‘water’. But natural-kind terms form a grammatically variegated class. Although they're all terms for kinds in some sense, they may be terms for kinds of object (like ‘tiger’, ‘mammal’, ‘fish’, ‘whale’) or for kinds of stuff (like ‘water’, ‘gold’, ‘aluminium’). It's generally assumed that this difference is not important for the issues which Kripke is concerned with. What does matter is that the kinds in question are natural kinds. So what makes a kind natural? There are two broad conceptions of nature which seem to be at play in the focus on natural-kind terms.