 One of the troubles with ontology is that it not only isn’t clear what there is, it also isn’t so clear how to settle questions about what there is, at least not for the kinds of things that have traditionally been of special interest to philosophers: numbers, properties, God, etc. Ontology is thus a philosophical discipline that encompasses besides the study of what there is and the study of the general features of what there is also the study of what is involved in settling questions about what there is in general, especially for the philosophically tricky cases. How we can find out what there is isn’t an easy question to answer. It might seem simple enough for regular objects that we can perceive with our eyes, like my house keys, but how should we decide it for such things as, say, numbers or properties? One first step to making progress on this question is to see if what we believe already rationally settles this question. That is to say, given that we have certain beliefs, do these beliefs already bring with them a rational commitment to an answer to such questions as ‘Are there numbers?’ If our beliefs bring with them a rational commitment to an answer to an ontological question about the existence of certain entities then we can say that we are committed to the existence of these entities. What precisely is required for such a commitment to occur is subject to debate, a debate we will look at momentarily. To find out what one is committed to with a particular set of beliefs, or acceptance of a particular theory of the world, is part of the larger discipline of ontology.