Possible Worlds for Modal Primitivists

Among the most remarkable developments in metaphysics since the 1950’s is the explosion of philosophical interest in possible worlds. This paper proposes an explanation of what possible worlds are, and argues that this proposal, the interpreted models conception, should be attractive to anyone who thinks that modal facts are primitive, and so not to be explained in terms of some non-modal notion of “possible world.” I articulate three constraints on any acceptable primitivist explanation of the nature of possible worlds, and show that the interpreted models conception meets the three constraints. 1 Possible Worlds and Modal Primitivism Among the most remarkable developments in metaphysics since the 1950’s is the explosion of philosophical interest in possible worlds. But what are those possible worlds? Perhaps a clue is provided by the fact that every instance of the schema (SC) it is possible that φ iff there is a w such that w is a possible world and ‘φ’ is true at w. is widely assumed to be true. (SC) reveals a systematic correspondence between certain modal facts and facts regarding the existence of possible worlds. To some philosophers, (SC) and associated claims held out the hope of providing an explanation in non-modal terms of those modal facts which can be expressed by idioms representable in quantified modal logic. Some even proposed that all modal facts could be explained in terms of facts about which possible worlds