Abstract

This paper will look at three closely interrelated questions about necessary a posteriori identities, in particular concerning natural kinds. First-ly, what is the semantic phenomenon responsible for a posteriori necessities in general, and theoretical identity statements concerning natural kinds in particular? I will argue that rigidity, as it is usually defined, cannot do the job for theoretical identity statements. Rather, a posteriori necessities are grounded in a semantic phenomenon that I have in earlier work called actuality-dependence. Secondly, what is the basis for this semantic phenomenon? In other words, what makes a given expression actuality-dependent, and thereby fit for appearing in a posteriori necessities? I will argue that actuality-dependence is grounded in our linguistic patterns and dispositions of application and interpretation. Thirdly and finally, what does this tell us about what essences are, and how we possess knowledge of them? I will claim that the view I am proposing gives direct support to a conferralist view of essences, at least when it comes to natural kinds. Moreover, the explanation of a posteriori necessities does not rely on independent essentialist premises; however, it does rely on essentialist beliefs or expectations on the part of ordinary speakers.