The (first) Cartesian argument for God’s existence can be summed up quite simply but understood only in the context of the larger work. As Descartes writes in the third meditation, on page 101, “By the word ‘God’ I mean an infinite substance, eternal, immutable, independent, omniscient, omnipotent, and that by I myself and all other existent things, if it is true that there are other existent things, have been created and produced. But these attributes are such—they are so great and so eminent—that the more attentively I consider them, the less I can persuade myself that I could have derived them from my own nature. And consequently we must necessarily conclude from all that I have previously said that God exists.” Descartes here explicitly gives us his definition of the God he is working with: infinite, immutable, eternal, independent, omniscient, omnipotent, and the creator of everything. Notably, Descartes does not include goodness in this list. The concept of perfection, says Descartes, does not admit of deception, because all deception is a sort of lessening. We may assume that Descartes therefore subsumes goodness under the banner of perfection, something which, while not listed in the description in Meditation III, is essential to the proof in Meditation V.
Descartes’ first and most substantial proof is a form of the classic ontological argument. It rests mainly on the assumption that the magnitude of reality of the effect cannot exceed the magnitude of reality of the cause. Thus, if we have the clear and distinct idea, or effect, of an infinite being with so many “great” and “eminent” properties that we do not possess, then the cause must be at least equal to the magnitude of reality of that effect, which seems to be infinite. The idea of a thing having more or less reality than another thing is somewhat alien to readers today, but basically signifies how perfect or independent a thing is.For example, if my copy of the Meditiations were burned in a fire, the other students’ copies would survive. The copies are independent of one another. However, if my copy of the Meditations were to burn, the whiteness of the cover would not survive, because the whiteness is dependent on the substance. The “accident” of whiteness is thus less perfect than the “substance” of the book. We can say, therefore, that because the whiteness of the book has less of an independent existence than the substance of the book, it is less real.
But more than a strange conception of a thing having more reality than another thing, there underlies Descartes’ argument the assertion that the concept of the infinite predates our concept of the finite. Without this assertion, we could simply say that God is an amalgamation of other concepts, like a unicorn or Gary Busey. As Descartes writes on page 101,
And I must not imagine that I do not conceive infinity as a real idea, but only through the negation of what is finite in the manner that I comprehend rest and darkness as the negation of movement and light. On the contrary, I see manifestly that there is more reality in infinite substance than in finite substance, and my notion of the infinite is somehow prior to that of the finite, that is, the notion of God is prior to that of myself. For how would it be possible for me to know that I doubt and that I desire—that is, that I lack something and am not all perfect—if I did not have in myself any idea of a being more perfect than my own, by comparison with which I might recognize the defects of my own nature?So we see here a two-part argument for the positive conception of the infinite: infinite substances are more real than finite substances; and the fact that there seems to exist some sort of standard by which to measure imperfection. Descartes does not attempt to prove either of these claims. But he achieves, through the argument resting on these two assertions, a basis for believing in a cause of his ideas, namely, God. Added to this, by way of the natural light, is the fact that God is not a deceiver, and Descartes has a mechanism for reasonably believing the content of his sense perception.
The statement that God is not a deceiver is somewhat akin to the statement that God is good, but it is not equivalent. God could very well not be a deceiver and still be totally unconcerned with human life. So Descartes has yet to remove himself from the generic monotheistic conception of God, and remains at this point a deist. At the end of the third meditation he allows himself a moment to reflect on the magnificence of the God he has just proved, the possessor of so many great properties and attributes. This God is, if one may say, a god of milk and water. Descartes is very careful to keep a broad enough conception of God that he does not offend the reigning Roman Catholic Church, but keeps God at enough of a distance to allow free and autonomous reign to the rationalism and humanism that prevailed in the intellectual circles of the time.
But what about the second proof? Descartes uses the concept of clear and distinct ideas to once again demonstrate God’s existence. He writes on page 120,
It is certain that I find in my mind the idea of God, of a supremely perfect Being, no less than that of any shape or number whatsoever; and I recognize that an actual and eternal existence belongs to his nature no less clearly and distinctly than I recognize that all I can demonstrate about some figure or number actually belongs to the nature of that figure or number. Thus, even if everything that I concluded in the preceding Meditations were by chance not true, the existence of God should pass in my mind as at least as certain as I have hitherto considered all the truths of mathematics. . .In this argument Descartes adds to his conception of God that God is a necessary being, or that God’s existence is a necessary part of God’s essence. This echoes very closely Saint Anselm’s response to Gaunilo’s objections to his ontological argument. So Descartes now has a sort of shortcut to trust in sensory perception, by reasoning that a clear and distinct idea of God has a property of necessary existence, and that a God containing all perfection would not be a deceiver, and thus one can trust the senses.
Throughout all this, Descartes never makes any statements about God being personal or interacting in any historical or direct way with the world or with human beings. While it could be concluded that such concerns are not relevant to the task of the Meditations, the conception of God as it stands in the Meditations is too close to a deist one to be ignored. Descartes does not say that God does not intervene in nature, perhaps fearing reproof from the Church, but it is not a stretch to assume that this is what he believes.
Bibliography
http://oregonstate.edu/instruct/phl302/philosophers/descartes-god.html