Nick: Can God create a rock he can't lift? Professor: Thomas Aquinas is not on the syllabus for this class. Nick: Can you answer the question? Professor: Mr. Haas... Nick: If you answer yes, then there exists a rock in the world that God can't lift. Ergo, he's not all-powerful. Answer no, and he can't create such a rock, again, not all-powerful. So, the very idea of an all-powerful god is a human creation and a flawed one, at that.