In Meditation Three of Descartes' Meditations on First philosophy he makes the argument that an omnipotent and infinite god exists. In this paper I'll reconstruct Descartes argument and evaluate its validity based on the soundness of its premises. Descartes' proof for the existence of god is: 1.) I think, therefore I am. 2.) I can not be mistaken about the ideas that I have. 3.) There must be at least as much formal reality (i.e., object of the idea) in the cause of an idea as there is objective reality (i.e., the idea it's self) of a perfect idea. (Otherwise something would come from nothing.) 4.) I have an idea of a perfect infinite being. 5.) Since I am imperfect. I do not have enough formal reality to be the cause of my idea of my idea of the perfect being. (My idea of perfection is the most objectively real idea I have.)
6.) There for the only possible formal cause of my idea of a perfect being is god, and I am not him.
Therefore, God must exist
Premise numbers one and two, can not be doubted. Although really not discussed much in Meditation three, they are essential for the rest of Descartes arguments. Premise number three shows that there can never be more objective reality in the effect than there is formal reality in the cause. Here is an analogy to explain the difference Descartes makes between formal reality, objective reality, and help to explain premise three. As an example we'll use a picture of my grand mother. A picture can be looked at for it's formal reality (as a chemical representation of her on a piece of paper), or for it's objective reality (as a representation of my grandmother). This might bring up the question,