Abstract

Philosophers have been referring to the “Kripke–Putnam” theory of naturalkind terms for over 30 years. Although there is one common starting point, the two philosophers began with different motivations and presuppositions, and developed in different ways. Putnam’s publications on the topic evolved over the decades, certainly clarifying and probably modifying his analysis, while Kripke published nothing after 1980. The result is two very different theories about natural kinds and their names. Both accept that the meaning of a naturalkind term is not given by a description or defining properties, but is specified byits referents. From then on, Putnam rejected even the label, causal theory of reference, preferring to say historical, or collective. He called his own approach indexical. His account of substance identity stops short a number of objections that were later raised, such as what is called the qua problem. He came to reject the thought that water is necessarily H2O, and to denounce the idea of metaphysical necessity that goes beyond physical necessity. Essences never had a role in his analysis; there is no sense in which he was an essentialist. He thought of hidden structures as the usual determinant of natural kinds, but always insisted that what counts as a natural kind is relative to interests. “Natural kind” itself is itself an importantly theoretical concept, he argued. The paper also notes that Putnam says a great deal about what natural kinds are, while Kripke did not. Moreover, a theory about names of natural kinds is to some extent independent of a theory of natural kinds themselves, to the extent that one can accept the one and reject the other, even when both are advanced by the same philosopher.