Abstract: This book is a study of the concept of necessity. In the first three chapters, I clarify and defend the distinction between modality de re and modality de dicto. Also, I show how to explain de re modality in terms of de dicto modality. In Ch. 4, I explicate the concept of a possible world and define what it is for an object x to have a property P essentially. I then use the concept of an essential property to give an account of essences and their relationship to proper names. In Ch. 6, I argue that the Theory of Worldbound Individuals—even when fortified with Counterpart Theory—is false. Chapters 7 and 8 address the subject of possible but non-existent objects; I argue here for the conclusion that there is no good reason to think that there are any such objects. In Ch. 9, I apply my theory of modality to the Problem of Evil in an effort to show that the Free Will Defense defeats this particular objection to theism. In Ch. 10, I present a sound modal version of the ontological argument for the existence of God. Finally, in the appendix, I address Quinean objections to quantified modal logic.

Keywords: Counterpart Theory, de dicto, de re, essence, essentialism, free will, modal logic, modality, necessity, ontological argument, Plantinga, possible worlds, proper name