  The power and appeal of basic possible world semantics is undeniable. In addition to providing a clear, extensional formal semantics for a  formerly somewhat opaque, intensional notion, cashing possibility as  truth in some possible world and necessity as truth in every such  world seems to tap into very deep intuitions about the nature of  modality and the meaning of our modal discourse. Unfortunately, the  semantics leaves the most interesting — and difficult —  philosophical questions largely unanswered. Two arise with particular force: 