Well lets begin there and if you think we've begun dealing with an impossible God, let me know. Here's the argument in simple expression:
- God's existence is possible.
- If God's existence is possible, then God exists in some possible world.
- If God exists in some possible world, then God exists in all possible worlds.
- If God exists in all possible worlds, then God exists in the actual world.
- If God exists in the actual world, then God exists.
Notes:
Premise (2) is just a technical explanation of the meaning of premise (1). A "possible world" is what philosophers mean by a "hypothetical situation".
This argument depends on a right understanding of "possibility" (which we've discussed in other posts). If something is logically possible then it is not necessarily false.
This argument also depends on a right understanding of "God". "God" is a logically necessary being. If he exists, then he
must exist and it would be inconceivable for him to
not exist. His non-existence would be just as inconceivable as 2+2=5.
If a logically necessary being exists in some possible world, then he exists in all possible worlds because that's what it means to be a necessary being.
So if it's possible for God to exist, then God certainly exists.