How do I know that God exists? More particularly, how do I know that he is not a figment of my imagination? I find within myself the idea of the most perfect being, of which I understand that existence is part of his nature. Although I can distinguish between existence and essence, I cannot separate existence from God anymore than I can separate triangularity from a triangle, or a mountain from a valley. I cannot think of God without existence just as I cannot conceive of a mountain without a valley.
There is an important logical difference between the conception of a mountain with a valley and the conception of God together with existence. The fact that a mountain cannot be thought without a valley, does not imply that mountains must exist; it only implies that if a mountain exists, there must be a valley as well.
In the terms of mathematical logic, we could perhaps analyze it, not as an existentially quantified sentence, but as a universally quantified one, Necessarily, for all x and all y, if x is a mountain, and y is a Valley, then there is a relation between x and y. But it need not be the case that a mountain exists. There is nothing contradictory about a flat earth. That is why one uses a universal instead of an existential quantifier. Shouldn’t we say the same thing about God? If I think that God, if He exists, also exists, that doesn’t imply that He exists.
That argument clearly isn’t cogent. As it stands it is a tautology and therefore proves nothing. All it says, one is tempted to say, is that there is an x and x is God. It shows that we cannot conceive of an existing God without conceiving of His existence. Could we conceive of God at all without existence? Descartes holds that we cannot.
Of course, using mathematical logic here is ahistorical. Though Russell read Descartes, Descartes did not read Russell. On a common reading ‘exists’ in Descartes argument functions as a predicate. It is precisely this use that Kant indicted in his purported refutation of what he, perhaps infelicitously, called the Ontological Argument. Existence according to Kant is not a predicate. As we have seen in the paragraph on the objections to St Anselm’s proof however, sometimes one does need to use ‘exist’ as a predicate, or in any case, to say that such and such a thing does exist. However that may be, using an existential quantifier to express the thought that the concept of God involves the concept of existence goes awry. If we merely say that there is an x such that x is God; the existence of God does not follow from an explicitation of the concept, rather God is said to exist. A judgement about God’s existence is put forward here. It therefore misrepresents Descartes’ argument to put it in terms of mathematical logic. It is better therefore to leave mathematical logic to the side here and to continue thinking about Descartes’ arguments for the existence of God in the terms in which he discusses them.
I cannot think of God, Descartes holds, without His existence. Therefore God cannot be separated from existence, so He must exist. God cannot be separated from existence because He is the most perfect being. Since existence is the highest perfection, it is impossible to conceive of God without existence. A non-existing God is logically impossible to conceive of, whereas one could conceive perfectly well of both, say, a horse with wings, and one without.
The objection to this line of reasoning lies to hand. What if the posited proposition, ‘God possesses all perfections’ is not itself necessary? Descartes retorts that if I think of God I necessarily attribute all perfections to Him in the same way as thinking of a triangle implies thinking of a figure with straight sides and three angles.
Moreover I cannot conceive of anything else whose existence is part of its essence.
The big question looming largely is why the professed certainty Descartes ascribes to his concept of God should be any reason for taking the propositions that follow from this concept to be true. Descartes’ proof in the fifth Meditation turns on his concept of truth. It is when we know what Descartes holds truth to be that we are able to understand why it is that he purports to be able to show that God exists by purely a priori argument.
In the third Meditation Descartes states that he considers an idea to be true if he sees it clearly and distinctly. The definitions of these crucial notions can be found in Descartes’ Principles of Philosophy, section 45. For an idea to be clear is for it to be present and accessible to the attentive mind. An idea is distinct if it is clear and sufficiently acutely separated from other perceptions to contain just that which is clear. So if an idea is true, it is present to my mind, I see it for what it is and I can tell it apart with great precision from other ideas. If we return to the third Meditation we see that ideas themselves strictly speaking aren’t true or false. Ideas are true or false only if they pertain to other things than themselves. If I have the idea of a flying horse that idea is not false; it would only be false if I judged that there was such a thing. Truth and falsehood in a strict sense are properties only of judgements. My idea of God is true or false only if I judge that He exists or doesn’t exist.
The judgement that God exists must be true, Descartes holds, since it is clear and distinct. It cannot be the case that I clearly and distinctly perceive an idea which is not by virtue of its being so perceived, true.
Descartes’ exposition of his idea of truth is closely involved with his first proof of God’s existence in the third Meditation. It is this proof that I turn to next. Then I shall discuss if the proofs cohere and how they reflect on the proofs of St. Anselm and St. Augustine.
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