natural kind a category of entities classically conceived as having modal implications; e.g., if Socrates is a member of the natural kind human being, then he is necessarily a human being. The idea that nature fixes certain sortals, such as ‘water’ and ‘human being’, as correct classifications that appear to designate kinds of entities has roots going back at least to Plato and Aristotle. Anil Gupta has argued that sortals are to be distinguished from properties designated by such predicates as ‘red’ by including criteria for individuating the particulars (bits or amounts for mass nouns) that fall under them as well as criteria for sorting those particulars into the class.
Quine is salient among those who find the modal implications of natural kinds objectionable. He has argued that the idea of natural kinds is rooted in prescientific intuitive judgments of comparative similarity, and he has suggested that as these intuitive classifications are replaced by classifications based on scientific theories these modal implications drop away. Kripke and Putnam have argued that science in fact uses natural kind terms having the modal implications Quine finds so objectionable. They see an important role in scientific methodology for the capacity to refer demonstratively to such natural kinds by pointing out particulars that fall under them. Certain inferences within science – such as the inference to the charge for electrons generally from the measurement of the charge on one or a few electrons – seem to be additional aspects of a role for natural kind terms in scientific practice. Other roles in the methodology of science for natural kind concepts have been discussed in recent work by Ian Hacking and Thomas Kuhn.
See also COUNT NOUN, ESSENTIALISM , PHI- LOSOPHY OF SCIENCE , QUALITATIVE PREDI – CAT. W.Har.