Twenty-five basic theorems in situation and world theory

object that actually exists but is uninstantiated. (p. 121) No one has gone further to develop the idea that there are two conceptions of possible worlds than van Inwagen in [1986]. He says: . . . Lewis did not content himself with saying that there were entities properly called ‘ways things could have been’; nor did he content himself with implying that ‘possible world’ was a heuristically useful stylistic variant on ‘way things could have been’. He went on to say that what most of us would call ‘the universe’, the mereological sum of all the furniture of earth and the choir of heaven, is one among others of these ‘possible worlds’ or ‘ways things could have been’, and that the others differ from it “not in kind but only in what goes on in them” (Lewis [1973], p. 85). And to suppose that the existence of a plurality of universes or cosmoi could be established by so casual an application of Quine’s criterion of ontological commitment has been regarded by most of Lewis’s readers as very exceptional indeed.