On its face, the notion of ontological commitment for theories is a simple matter. Theories have truth conditions. These truth conditions tell us how the world must be in order for the theory to be true; they make demands on the world. Sometimes, perhaps always, they demand of the world that certain entities or kinds of entity exist. The ontological commitments of a theory, then, are just the entities or kinds of entity that must exist in order for the theory to be true. End of story (compare Rayo 2007: 428).