This is my very favorite argument for God, because it is so wonderfully sophistic, solipsistic, and (in later formulations) linguistically slapstick:
- If God is defined such that God exists, then God really does exist.
- "God" is defined as a being which, among other things, exists (necessarily)
- Therefore, God exists.
Given the tenuousness of the first premise, I really don't think we ought to waste loads of time on this one.