Even if we assume that existence can be seen to be a predicate that something can have, I believe that the ontological argument fails in proving that existence is a predicate of God. Like Hume has argued, the whole basis of the ontological argument, especially in Descartes’ more rational format, in attempting to prove the existence of God using an a priori argument is faulty. I take the view that the existence of things can only be proved empirically, it isn’t possible to take the idea of God in one’s mind, apply pure logic to the idea and then come to a conclusion based entirely in the external, observable universe. God exists in the mind, but you can say no more than that without evidence.
Moreover, existence cannot be seen to be a predicate of God because, more generally, existence is not a predicate. I argue this because, as Hume and Kant have written, having an idea of something and then having it exist changes nothing about the nature of the thing. In fact “whatever we conceive, we conceive to be existent” (Hume, Treatise on Human Nature). Therefore, unlike describing a bird as blue, describing it as existing changes nothing about our perception of or in fact the bird itself at all.
Some, however, may argue that existence can be seen to be a predicate because having an object exist does change the way we conceive it. For example, some may, after reading Plato, insist that our perception of Socrates is changed if we learn that Socrates existed. Similarly, to conceive of God existing and not just a mere figment of many believers’ imagination adds something to the concept of God. However, I would argue that it doesn’t, and this is simply a misuse of language. Although I accept that