When considering God as "a substance that is infinite, eternal, immutable, independent, supremely intelligent, supremely powerful, and which created both myself and everything else," the Meditator realizes that the idea of God must have far more objective reality than he has formal reality: God is an infinite substance whereas he is only a finite substance. Since the idea of God cannot have originated in himself, he concludes that God must be the cause of this idea and must therefore necessarily exist.
The Meditator counters the argument that he might conceive of an infinite being through negation, that is, through conceiving of it in contrast to his own finite being. Doubts and desires come from an understanding that we lack something, and we would not be aware of that lack unless we were aware of a more perfect being that has those things which we lack.
While he can doubt the existence of other things, he cannot doubt the existence of God, since he has such a clear and distinct perception of God's existence. The idea has infinite objective reality, and is therefore more likely to be true than any other idea.
The Meditator then entertains the possibility that he may be supremely perfect, that all his deficiencies are potentialities within him, and that he is slowly improving toward perfection. If perfection is a potentiality within him, then it is plausible that the idea of God could be conceived in him without any outside cause. The Meditator rejects this possibility for three reasons: first, God is all actual and not at all potential; second, if he is constantly improving, he will never attain that perfection where there is no room for improvement; and third, potential being is not being at all: the idea of God must be caused by something with infinite actual being.
If the Meditator could exist without God, he would have come to be out of herself, or from his parents, or from some other being less perfect than God. If he derived his existence from himself, there is no reason that he should have doubts and desires. He also cannot escape this reasoning by supposing he has always existed and never had to come into being. There is no reason that he should continue to exist unless there is some force that preserves him, that creates him anew at every instant. As a thinking thing, he should be aware of that power of preservation though it came from within him.
If his parents or some other imperfect being created him, this creator must have endowed him with the idea of God. If this creator is a finite being, we must still ask with respect to it how it came to possess the idea of an infinite God. We can trace this chain back through countless creators, but we must ultimately conclude that the idea of God can originate only in God, and not in some finite being.