Natural Kind Terms, Rigidity and the Path towards Necessity

Abstract

According to S. Kripke, two important similarities between natural kind terms and proper names are that both types of expressions are rigid designators and that they appear in identity statements that are necessary if true ; Kripke denominates these types of statements containing natural kind terms “theoretical identities”. Nevertheless, Kripke claims that the latter similarity follows from the former. In this paper the author has a threefold aim. Firstly, he contends that it can be held that natural kind terms are rigid designators. Secondly, he argues that the conception of natural kind terms as rigid designators hinders the establishment of the truth of theoretical identities and hence of their necessity. Thirdly, he disputes some of Kripke’s claims of a metaphysical character to support the truth and necessity of theoretical identities.