This dissertation is a defense of a logical criterion of ontological commitment, an argument for neutral commitment pluralism, a defense of a useful paraphrase relation, and an examination of nihilism.
Roughly, a criterion of ontological commitment tells us what must exist for a theory to be true. Chapter one defends a logical, rather than modal, criterion of ontological commitment and argues for neutral commitment pluralism. Roughly, neutral commitment pluralism is the thesis that a good criterion of commitment does not choose any particular logic for determining commitments, but instead uses different ones, and so yields a variety of verdicts on the commitments of a given theory.
It seems as though we can sometimes “paraphrase away” ontological commitments. Consider ‘I got caught in traffic’. It initially seems committed to a thing, traffic, with catching powers. How else could that sentence be true? Well, if we paraphrase it using a different sentence that makes no mention of traffic (perhaps ‘My car moved slowly because the road was crowded’) our paraphrase may (somehow!) show that the initial sentence was never committed to traffic in the first place. Chapter two explains a paraphrase relation that is useful for avoiding commitment.
Nihilism, the theory that there is nothing, is particularly salient in this context. One might think that nihilism has no commitments at all (its truth does not require that anything at all exist). But it turns out that nihilism and some principles concerning truth and predication jointly imply that something exists (i.e., imply that nihilism is not true). As a result, that argument against nihilism can be used to answer why there is something rather than nothing, and a modal version of it can be used to answer why there must be something rather than nothing. Chapter three deals with those arguments in depth and defends a distinction between existence in vs. at a world. Chapter four addresses some implications of the existence in/at distinction for metaontology generally and ontological commitment in particular.