Possible Worlds, The Lewis Principle, and the Myth of a Large Ontology

It is a commonplace of modal metaphysics that belief in possible worlds not only burdens one with a large ontology but also raises metaphysical problems concerning their existence and identity conditions and epistemological problems concerning the justification of one’s belief in them. In this paper, we challenge this commonplace and show that belief in possible worlds doesn’t necessarily burden one with a large ontology or with the metaphysical and epistemological problems noted. We argue specifically for the claim that the most fundamental existence principle of world theory is not only true in small models, but is derivable from analytically true principles. If this is so, it puts the lie to the view that a commitment to possible worlds entails a commitment to a large ontology. Moreover, the particular theory we use to support our claims precisely addresses the metaphysical problems about the existence and identity of worlds and offers a solution of the epistemological problem of justifying belief in worlds.