[re-post from 07/14/2011]
The central questions of ontology are “what sorts of things fundamentally exist?” and “what is it for something to fundamentally exist?” The answer is usually conceived in terms of a sort of “object” that is a building block, such as atoms, or minds/ideas (idealism), etc. I, however, do not believe individual objects, as usually conceived, fundamentally exist. They exist only superficially. This is exemplified by Gilbert Ryle’s thought experiment “what is wrong with saying there are three things in a field; two cows and a pair of cows?” The commonsense objection would be that the cows “actually” exist, whereas the “pair” is merely a conceptual projection. But why should this be? I can simply respond that the cow is a conceptual projection – it is really a collection of atoms arranged cow-wise. And so on. Individual “objects” are convenient conceptual constructs – they do not have ontological status. We merely use the knife of analysis to divide the world in ways relevant to us as a certain sort of creature.
What, then, do we mean when we say something like “the chair exists?” I think Princeton philosopher Richard Chappell has an excellent answer. The problem is that we use the word “exist” in two different ways. Usually, we are speaking of superficial existence, which makes no ontological claim. It does not assert that chairs are one of the “fundamental sorts of things” that reality is “made of.” Rather, it distinguishes between possible worlds. When I say that the chair exists, I am distinguishing this world from a possible world where that subdivision of reality that we happen to conceptualize as a chair is not there, or, more accurately, is not sufficiently chair-like.
The other sort of existence claim is one of fundamental existence – it is an ontological claim. It is an assertion that the sort of thing described is what reality fundamentally “is.” In other words, a fundamental existence claim deals with what sorts of things make up logically possible worlds, whereas a superficial existence claim serves to differentiate the actual world (or the possible world representing, vis a vis exact correspondence, the actual world), from one or more other possible worlds, both logical and nomological.
The project of ontology, then, is to investigate the sorts of things that make up possible worlds. The sorts of things that make up all possible worlds by definition exist in all possible worlds. Thus, we can logically derive the following: That which exists fundamentally exists necessarily. This fits in with my broader view that one of the main projects of metaphysics is to chart the realm of possibilities.
Rational A Priori 