t for dreaming is that if it’s possible that we are dreaming, we cannot have empirical beliefs. It is possible that we are dreaming, so we can’t have certain knowledge regarding empirical beliefs. To further illustrate his skepticism regarding empirical beliefs, he proposes the purely theoretical "evil demon" argument. In it he argues that if it is possible that we are deceived by an evil god, then we cant know anything with certainty. Since it is possible that we are being deceived by an evil god, then we cannot know with certainty. These arguments were made to establish that it is possible that either through perceptual error or cognitive dysfunction, we may be deceived and not know with certainty. In light of his newfound credo of doubt and skepticism, he finds himself questioning his very existence. If in fact it is possible that an evil god is tricking him, could it also be possible that he doesn’t really exist at all? To prove his existence he uses the maxim of "Cogito ergo sum", or "I think therefore I am". The only thing that could not be doubted is that he thought something, even if it was thinking he was dreaming or being tricked, or thinking that he didn’t have a body. This was what he saw as the first true principle and the basis for any further inquiry. This led him to suppose that the essence of being was thinking, and furthermore, that the mind was separate from the body.This was a foundation, but it had one problem. It only proved that he existed. He had no way to show that his surroundings, including other people, existed. Descartes realized for this and other reasons that he needed to prove God’s existence. God could be the only guarantee that our clear and distinct ideas are true, and that we are not being tricked by an evil demon. For this, Descartes was happy enough to use a version of Anselm’s ontological proof to argue that the idea of a perfect God must have a caus...
