Abstract

I begin by introducing the ideas of possible worlds, books on worlds, and essential properties. A possible world is a broadly logically possible state of affairs that is maximal. Furthermore, for any possible world W and proposition p, let the book on W be the set S of propositions such that p is a member of S if W entails p. Finally, an object x has property P essentially if and only if x has P and has it in every world in which x exists. I use the above three concepts to give a sound argument for the conclusion that human persons are essentially immaterial.