Augustine's apologetic on faith.
1. Think with Assent
2. Hypothetical acceptance
3. Trusting credible authority
4. compulsion of the truth
5. Surrender the will

I doubt
if there is doubt, then there must be knowledge-  truth outside mind
if there is knowledge, then there must be God



norman malcolm
If God doesn't exist, he can't come into existence, his existence would be impossible. If God does exist He can't cease to exist or he would not be God. God's existence is necessary or impossible.
God's existence is not impossible since it is not self contradictory. so God's existence is necessary.

leibniz
Anything that exists has an explanation of it's existence, either in the necessity of it's own nature or in an external explanation

The universe has an explanation for it's existence, and that explanation is grounded in a necessary being.

The universe exists.   Therefore the universe has an explanation for it's existence

Therefore the explanation of the existence of the universe is grounded in a necessary being.

Therefore God, a necessary being exists