Actually, it seems I misunderstood Craig's argument myself.
To pin down my own confusion, which I think also highlights an issue with the argument, the issue surrounds "explanation".
Something that exists of its own accord doesn't actually require any explanation. Right?
But, in premise (1), it is considered an explanation that something exists "in the necessity of its own nature".
So then we hit premise (2): If the universe has an explanation of its existence, then that explanation is God.
BUT, hang on. It was here that I injected the theological idea that something always existing in and of themselves requires no explanation.
Which for me actually turned this premise into:
- (2') If the universe has an explanation of its existence not found in the necessity of its own nature, then that explanation is God.
I believe the argument appears to follow because in our heads (at least mine), we are equivocating on what is an "explanation" in premise (1) and what isn't in premise (2). If we switch the role of "universe" and God" around, the argument still appears to work. Which shows it is highly suspect.
- 1. Everything that exists has an explanation of its existence, either in the necessity of its own nature or in an external cause.
2. If God has an explanation of his existence, that explanation is the Universe.
3. God exists.
4. Therefore, God has an explanation of his existence (from 1, 3).
5. Therefore, the explanation of God's existence is the universe (from 2, 4).
Evidently, the missing premises are justification for why the Universe can't just necessarily exist of its own nature.
Otherwise the argument becomes a bit circular in assuming what it is setting out to prove.