You: If the propositions of your argument are correct, then might not God not be?

Aaron: No, God is necessary. That is the entire point of my argument.

You: But if you cannot prove that God is necessary in the first place, then you cannot use him as the necessary being in the conclusion of the argument. The necessary thing might be a mindless, deistic prime mover for all you know.

Aaron: No, no, no. The very nature of God is proof for his existence.