By far the most influential critique of the ontological argument is that of Immanuel Kant. Kant, himself a theist, argued that the ontological argument illicitly treats existence as a property that things can either possess or lack. According to Kant, to say that a thing exists is not to attribute existence to that thing, but to say that the concept of that thing is exemplified in the world. The difference, and its significance for the ontological argument, are described below.
Most statements of the form “S is p” are true if and only if there is something in the world that is picked out by the name S, and the thing picked out by the name S satisfies the description “is p”.
Thus God created the heavens and the Earth is true if and only if there something in the world that is picked out by the name God, and that thing created the heavens and the Earth. This analysis is simple, but it works for most statements of the form “S is p”.
Similarly, most statements of the form “S is not p” are true if and only if there is something in the world that is picked out by the name S, and that thing satisfies the description “is not p”.
“God exists” (or “God is existent”) appears to be of the form “S is p”; it appears to attribute a property, existence, to a subject, God. “God does not exist”, meanwhile, appears to be of the form “S is not p”; it appears to deny a property, existence, to a subject, God. If the above analyses of statements of these forms applies to attributions of existence and non-existence, then “God exists” would be true if and only if there is something in the world that is picked out by the name God and that thing satisfies the description “exists”. “God does not exist”, meanwhile, would be true if and only if there is something in the world that is picked out by the name God and that thing satisfies the description “does not exist”.
There are immediate problems with both of these analyses, however. Consider first the analysis of the truth-condition of “God exists”: there is something in the world that is picked out by the name God and that thing satisfies the description “exists”. The second clause of this analysis appears to be redundant. “There is something in the world that is picked out by the name God and that thing satisfies the description exists” says nothing more than “There is something in the world that is picked out by the name God. Why do we need the addition “and that thing satisfies the description exists”? Already, then, there is a clue that “God exists” is rather different in logical form to “God created the heavens and the Earth”.
Next consider the analysis of truth-condition of “God does not exist”: there is something in the world that is picked out by the name God and that thing satisfies the description “does not exist”. In order for “God does not exist” to be true, then, God would have to both exist (in order to be picked out by the name God) and not exist (in order to satisfy the description “does not exist”). Clearly this could never be the case; nothing can both exist and not exist. If existence is a property that can be attributed to subjects like any other, then “God does not exist” can never be true, and God’s existence is necessary.
This may not seem to be a problem for the advocate of the ontological argument; after all, classical theism holds that God is a necessary being. However, what holds for attributions of non-existence to God also holds for attributions of non-existence to anything else. “The tooth-fairy does not exist”, on the analysis suggested above, is true if and only if there is something in the world that is picked out by the name The tooth-fairy, and that thing satisfies the description “does not exist”. Again, “Middle Earth does not exist” is true if and only if there is something in the world that is picked out by the name Middle Earth, and that thing satisfies the description “does not exist”. Neither of these statements, and no other statements like them, could ever be true. What we have here is an ontological argument for the existence of everything!
Clearly, attributions of existence and non-existence are not to be treated in the same way as attributions of other properties. An alternative analysis of statements of the form “S exists” or “S does not exist” is required, one that does not require something to both exist and not exist in order for “S does not exist” to be true. We have already encountered the alternative analysis of “S exists”; to get it, we simply drop the redundant clause “and that thing satisfies the description exists”. “S exists”, then, according to the proposal, is true if and only if there is something in the world that is picked out by the name S. Similarly, “S does not exist” is true if and only if there is not something in the world that is picked out by the name S. Existence and non-existence are thus seen not as a matter of things possessing or lacking a property, but as concepts corresponding or not corresponding to the world.
This, though, presents a problem for the ontological argument. For the ontological argument rests on a comparison between, on the one hand, a God that exists, and, on the other, a God that does not. A God that exists, the ontological argument assumes, is better than a God that does not.
If, as has been argued here, existence is not a property that objects possess or lack, but a correspondence between a concept and the world, then this is comparison is illicit. For in that case, God existing is a matter of the concept of God being exemplified, and God not existing is a matter of the concept of God not being exemplified. In both cases, though, the concept of God that either is or is not exemplified is exactly the same.
The comparison on which the ontological argument rests is therefore a comparison between two identical concepts of God, one exemplified, and the other not. As these two concepts of God are identical, they cannot be contrasted, and so no conclusion can be drawn from any such contrast. The ontological argument therefore fails, because its assumption that an existent God is greater than a non-existent God is false; the two are equal in greatness, because they are identical.
Topic: Ontological arguments: Existence is not a real predicate