12. The Argument from the Origin of the Idea of God

This argument, made famous by Descartes, starts from the idea of God and seeks to show that only God himself could have caused us to have an idea of God in our minds.  Dr. Peter Kreeft and Father Ronald Tacelli have outlined this beautifully in the Handbook of Catholic Apologetics. 

1. "We have ideas of many things.
2. These ideas must arise either from ourselves or from things outside us. 
3. One of the ideas we have is the idea of God- an infinite, all-perfect being.
4. This idea could not have been caused by ourselves, because we know ourselves to be limited and imperfect, and no effect can be greater than its cause.
5. Therefore the ideas must have been caused by something outside us that has nothing less than the qualities contained in the idea of God.
6. But only God himself has those qualities.
7. Therefore God himself must be the cause of the idea we have of him.
8. Therefore God exists" (Handbook, pgs. 73-74).