Since I cannot think of God but as existing, existence is inseparable from God and therefore God exists. There is a funny way that Descartes is using existence here. Later we will look at it more clearly with Kant but let us just see what objections we can raise right now at a more elementary level. When we say that we have an idea of a mountain and a valley, we are not saying that we have an idea of something that exists in the world yet, but exists in itself. Try to think of a mountain that does not exist. To say that it does not exist is saying that it is nothing. You cannot say that there is a mountain that does not exist, because then you are saying that there is something that is nothing. If there is nonexistence then there is no thing, therefore there cannot be something that is nothing. So the idea of existence is tied intimately to whatever thing that we can conceive, and is not just a special case with God. Had Descartes seen it this way, he may have tried to wiggle his way out using his clear and distinct clause. God is special because I clearly and distinctly perceive the idea of God, and that is the only the idea I clearly and distinctly perceive, so the argument still works for God. We"ll see whether this holds up or not.
Kant's argument against the ontological is based in predication. When we make a statement like "God is omnipotent" we have two parts, a subject and a predicate. The subject is God and the predicate is omnipotence, the subject is some object and the predicate is some property. The linking word "is" is saying that the subject has this property. Let us look at the idea of a triangle. When we say "triangle," we mean a thing that has three angles equal to two right angles. The triangle is the subject and having three angles equal to two right angles is a property of the subject. If I say that a triangle does not have three angles then there is a contradiction.
