Do most philosophers treat possible worlds as "real" ontological entities? That seems a bit extravagant to me. But here's the dilemma. If we take possible worlds as mere constructions, or "useful fictions", as I'm inclined to do, then we cannot use them to ground metaphysical possibility. For in constructing these "worlds", we must choose and impose a framework of contraints (e.g. the laws of classical logic, or of physics) regarding what we will allow in them. But that makes modality inherently relational: P is possible or not according to framework F; but there is no 'absolute' or transcendant framework which allows us to say that P is possible, simpliciter.
So suppose instead that there is such a transcendent framework, as provided by the set of "objectively real possible worlds". We can then say that P is metaphysically possible (i.e. possible simpliciter) iff P is true in some ORPW.
But, given that all we have epistemic access to is the actual world, how could we know anything about these possible worlds or their contents? How are we supposed to know what set of constraints they are governed by? How could we even guess? What's the basis for this wild metaphysical theorising?
Further, what does it even mean to say that something is metaphysically "possible", or that "the world could have been that way"? I can't make any sense of it. There's the way things are, actually, and then there's the way things are in other possible worlds, but what's the connection?
In what sense are other possible worlds supposed to be really possible? What does it mean to say, for example, "the universe could have been such that Kerry got elected instead"? Are we saying that our world could have been a different possible world? Isn't this utterly nonsensical?
Or perhaps it isn't a claim about the identity of these worlds, but rather, about which of them got actualized. The claim might be understood as: "Our world happens to be actual. But it need not have been. Any other possible world might have been actualized instead -- e.g. the one where Kerry became president." I'm not sure this makes any more sense though. What does that "might" mean, after all? Presumably it's a claim about metaphysical possibility -- so does that mean there is another possible world wherein the Kerry-world is actualized?
I'm so very confused. Please help!