78 Pacific Philosophical Quarterly 79 (1998) 78–97 0031–5621/98/0100–0000 © 1998 University of Southern California and Blackwell Publishers Ltd. Published by Blackwell Publishers, 108 Cowley Road, Oxford OX4 1JF, UK and 350 Main Street, Malden, MA 02148, USA. Abstract: J. L. Mackie’s famous claim that Locke ‘anticipates’ Kripke’s Causal Theory of Reference (CTR) rests, I suggest, upon a pair of important misunderstandings. Contra Mackie, as well as the more recent accounts of Paul Guyer and Michael Ayers, Lockean Real Essences consist of those features of an entity from which all of its experienceable properties can be logically deduced; thus a substantival Real Essence consists of features of a Real Constitution plus logically necessary objective connections between them and features of some particular Nominal Essence. Furthermore, what Locke actually anticipates is the most significant contemporary challenge to the CTR: the qua-problem. 1. Locke’s ‘Anticipation’ of Kripke Near the outset of the Third Book of An Essay Concerning Human Under- standing, Locke draws a crucial distinction between what he calls a Real Essence, the “unknown Constitution of Things, whereon their discoverable Qualities depend”, and a Nominal Essence, “that abstract Idea, which the General, or Sortal Name stands for”, that is, the set of necessary and sufficient conditions for the application of a term (III iii 15). On this account, the Real Essence of gold is whatever features of its constitution are in fact responsible for its properties, while its Nominal Essence is the set of ideas of observable qualities, such as ‘heavy’, ‘yellow’, ‘malleable’, REFERENCE AND NATURAL KIND TERMS: THE REAL ESSENCE OF LOCKE’S VIEW BY P. KYLE STANFORD