ABSTRACT
One of the most central and fundamental concepts at the heart of western philosophy has been the concept of essence. The essence of a thing is what it is: not just what it happens to be, but what it has to be in order to be the thing it is, or the kind of thing it is. This idea has its origin in the awareness that there are limits to how much something can change and still be the same thing, or the same kind of thing. The essence of a thing (or kind) is what cannot change without the thing turning into something else: it is what is necessary for it to be what it is. One way of specifying the essence of a thing is to list the conditions (or properties) that individually are necessary, and that together are sufficient, for the thing to be what it is. Since we are dealing with what a thing is, with what it is in its innermost being, as it were, the concept of essence tends to be a realist one: essences are thought of as existing independently of our perceptions, our language, and our understanding. They are a part of reality that we must discover. In medieval Scholastic terminology, the realist claims that essences are de re, ‘of the thing’ itself.
