I really feel that isn't a good example. As far as I know, only humans post on the internet, so it's safe to assume I'm human. All humans are mammals. All humans and mammals have brains, so it's safe to assume I have a brain. What would you say to a person of another faith to convince them you're right and they're wrong? The Deist arguement is the most convincing to me. They argue that God exists, but he only created the universe and never intervened in this world. He only observes. How could you prove that this is not true?