Essence, Modality, and Identity

Abstract

Suppose that identity-and therefore generalized identity, if it purports to be a bona fide notion of identity at all-not only has all the usual non-modal features (reflexivity, symmetry, transitivity, obeys something akin to Leibniz's Law, and so on), but also holds with necessity. If that is so, it seems that what might be called the identity-based essentialist can easily say why essence implies necessity. As Leech puts it, 'statements of essence are a special case of statements of identity.Statements of identity are necessary. Hence, statements of essence are necessary too ' (p. 13). Yet according to Leech, identity-based essentialism 'just moves the bump in the carpet', since one may now reasonably ask why one should agree that generalized identity implies necessity (p. 14). Why, just because there is no difference between a thing's being Plato versus its being both Plato and human, should it therefore follow that Plato is necessarily human? Leech argues that in order to bridge this new gap one can either account for necessity in terms of essence, or account for essence in terms of generalized identity in the way we envisage-but one cannot do both, 'on pain of circularity' (p. 16).We disagree. In fact, there are a number of safe and non-circular routes from generalized identity to necessity for the identity-based essentialist to choose from. Leech considers only one, which centers around a generalization of the classic proof of the necessity of objectual identity due to Barcan (1947) and Kripke (1971). After laying out the necessary background ( §1), we present a more direct proof that shows why one should agree that generalized identity implies necessity, and argue that neither our proof nor the generalized Barcan-Kripke proof tangles the essentialist up in any circularity ( §2). As we said before, Leech is not alone in worrying about a purported 'gap' between essence and necessity for the essentialist to bridge, although what that gap is, exactly, gets described by different authors in rather different ways, including by Leech. So after dealing with the epistemic challenge of providing reasons to believe that generalized identity implies necessity, we propose several full-blown accounts of necessity in terms of identity, and use them to address a further metaphysical challenge of describing in detail how it is that generalized identities generate necessities ( §3). Thus we conclude that identity-based essentialism deserves serious consideration in discussions of the nature and source of metaphysical modality.