Meditation 3 — Of God: That He Exists

Descartes closes his eyes, turns away from his senses, and takes stock of what he knows with certainty. He is a thinking thing. He seems to perceive clearly and distinctly that the cogito is true — but a nagging worry remains: what if a supremely powerful God (or deceiving spirit) has made him so that he is wrong even about what seems most evident? To settle this he must ask whether God exists, and what God's nature is.

He begins by classifying ideas. Some appear innate (the idea of a thinking thing), some adventitious (the idea of the sun as I see it), some factitious (the idea of a hippogriff I construct myself). Ideas have what he calls objective reality — the degree of being they represent. A stone's objective reality is less than a person's; a person's is less than God's. Whatever the cause of an idea, the cause must have at least as much formal reality as the idea has objective reality. A finite, imperfect cause cannot produce an idea with more objective reality than itself.

Now the key inference: in Descartes's mind there is an idea of God — of an infinite, all-knowing, all-powerful, supremely perfect being. This idea has the highest possible objective reality. He himself is a finite and imperfect being and could not be its adequate cause. Therefore there must be an actually existing being with infinite and perfect formal reality that caused this idea in him. That being is God. And since God is perfect, God is not a deceiver — deception implies imperfection. Therefore Descartes can now trust that whatever he perceives clearly and distinctly is true, because a perfect God has given him faculties reliable when used correctly. The argument is long and difficult. But its effect is decisive: it defeats the evil deceiver hypothesis by replacing the hypothetical deceiver with an actually existing non-deceiving God.