 Because the term “essentialism” recurs with different meanings in discussions of human nature and because some of the theoretical claims thus summarised are assumed to be Aristotelian in origin, it is worth spending a moment here to register what claims can be singled out by the expression. The first, purely classificatory conception just discussed should be distinguished from a second view that is also frequently labelled “essentialist” and which goes back to Locke’s concept of “real essence” (1689: III, iii, 15). According to essentialism thus understood, an essence is the intrinsic feature or features of an entity that fulfils or fulfil a dual role: firstly, of being that in virtue of which something belongs to a kind and, secondly, of explaining why things of that kind typically have a particular set of observable features. Thus conceived, “essence” has both a classificatory and an explanatory function and is the core of a highly influential, “essentialist” theory of natural kinds, developed in the wake of Kripke’s and Putnam’s theories of reference.