Descartes Ontological Argument for God (Meditations on First Philosophy)
1. Truth must be something we can trust beyond a doubt to be true
2. Our very act of thinking proves our existence to be truth (Congnitus Ergo Sum)\
3. Man can only understand something that he has previously conceived
4. Man can only conceive something he has previously experienced or can extrapolate from experience
5. Infinite is inherently inconceivable to finite beings, because of the inherently contradictory nature
6. God is an infinite being
7. Therefore, the idea of God cannot have originated from man, it must have come from God
8. In order to implant the idea God must exist
Note: this only proves the existence of an infinite power that can interact at a intellectual level with man, not necessarily that God is a flesh and blood being