The Definitional Conception of Essence

An essential property of a thing tells us about the real definition of that thing. In this dissertation, I argue that a real definition states conditions on the identity of things and explains how they differ from other individuals or members of other kinds. I then apply this account to show that some essential properties are discovered by science. I also argue contrary to reductionist accounts of essence and show that several of Kit Fine's applications of the notion of essence to ontological dependence and to the reduction of modality, are spurious. Finally, I argue that the real definition of each human person accounts for their personal identity over time.