In the course of the Third Meditation, Descartes constructs an argument for the existence of God that starts from the fact that he has an idea of an infinite being. The argument is intricate. It invokes the metaphysical principle that “there must be at least as much reality in the efficient and total cause as in the effect of that cause” (7:40). This principle is put forward as something that is “manifest by the natural light” (7:40), which itself is described as a cognitive power whose resu