Possible Worlds

In many cases, philosophers consider something possible if it hasn't been shown to be impossible.  So much the better for asserting possibly God exists.  But suppose we wanted to confer support on that proposition anyhow.  As any good theist should be, we aren't satisfied with relying on the prevalent attitudes among philosophers.  Can we show that possibly God exists?  Sounds easy enough, doesn't it?  I mean come on, all these arguments for God's existence...at least cumulatively they should give us a remote possibility.

This is where philosophical language is tricky if we don't pay close attention.  There is a difference between asserting what's possible to be known, and asserting what's possible period.

For example:
It's possible that it will rain today.
It's impossible for Clark Kent to jump over a tall building in a single bound.

These are normally taken to be a statements about the actual world given what we know.  In the first case, given what we know about weather systems, we maintain that rain is epistemically possible.  In the second example, given what we know about the laws of physics, we might intend to say that this feat is physically impossible.  There are other forms of possibility that philosophers talk about.

We wouldn't say that it's logically impossible for Clark Kent to clear a tall building.  But we would say that it's logically impossible for 2+2=5.  Thus, in that sense, it is possible for Clark Kent to jump over a tall building in a single bound.  Perhaps the laws of nature could have been different such that this would be permitted (interestingly, some have argued that he laws of nature could not have been different).  Assuming we think the laws of nature might have been different, we could say that it's metaphysically possible for Clark Kent to make his jump.

So to which kind of possibility do we refer when we say that God's existence is possible?  Metaphysical possibility ... or is it broadly logical possibility?  It depends on who you ask.

And thus, as far as I can see, a posteriori arguments for God's existence won't help the theist show that God exists is metaphysically possible.  I'm honestly not sure (and this is a statement about my ignorance) how one would go about showing that something is metaphysically possible.  Perhaps this is why philosophers tend to assume it unless shown otherwise?  We can show that something is conceptually incoherent and thus logically (and I will assume this entails metaphysically) impossible.  But how do we show something is metaphysically possible if it isn't already subsumed under what's physically possible?  Does this require mere conceptual analysis?