Objections to the Ontological Argument
The ontological argument is, roughly, the argument that God, being that than which no greater can be conceived, must exist, for if he did not then it would be possible to conceive of an existent God, which would be greater than that than which no greater can be conceived, which is absurd. The ontological argument is the most maligned of the arguments described on this site. It has critics representing all theological positions, including the classical theist Aquinas, the non-classical theist Kant, and the atheist Hume. Few now defend the ontological argument, but it has not been abandoned altogether.
Gaunilo’s Objection to the Ontological Argument: The Perfect Island
The earliest critic of the ontological argument was a contemporary of Anselm’s, the monk Gaunilo of Marmoutier. Gaunilo did not identify any specific fault with the argument, but argued that there must be something wrong with it, because if there is not then we can use its logic to prove things that we have no reason to believe to be true.
For instance, Gaunilo argued, it is possible to construct an argument with exactly the same form as the ontological argument, that purports to prove the existence of the perfect island: the perfect island must exist, for if it did not then it would be possible to conceive of an island greater than that island than which no greater can be conceived, which is absurd.
If the ontological argument works, then, according to Gaunilo, the argument for the existence of the perfect island works too. The two arguments have the same logical form, and so they stand or fall together. The argument for the existence of the perfect island, though, is clearly spurious; we have no reason to believe that the perfect island exists. Gaunilo’s argument must be rejected. Unless the theist can point to some relevant difference between his argument for the existence of God and Gaunilo’s argument for the existence of the perfect island, then, then he will have to abandon the ontological argument for the existence of God.
Responses to Gaunilo
Gaunilo’s objection to the ontological argument has been criticised on several grounds. One problem with it concerns the idea of a perfect island. A perfect island, presumably, is one with an abundance of lush palm trees and pristine beaches. The more of these an island has, the better it is. There is, however, no intrinsic maximum number of trees or beaches that an island could have; for any island that can be imagined, there is another, greater island, with one more palm tree and one more beach. There is, then, no island than which no greater island can be conceived. The concept of the perfect island is incoherent; there can be no such thing.
The concept of a perfect God, on the other hand is not incoherent. Power, knowledge, and the other qualities of God all have upper limits which when reached cannot be passed. There is, then, a difference between Gaunilo’s argument for the existence of the perfect island and Anselm’s argument for the existence of God that advocates of the ontological argument can cite as a reason for rejecting the former without committing themselves to also rejecting the latter.
Kant’s Objection to the Ontological Argument: Existence is not a Predicate
The most influential criticism of the ontological argument is that of Immanuel Kant. Kant thought that because the ontological argument rests on the judgement that a God that exists is greater than a God that does not, it rests on a confusion.
According to Kant, existence is not a predicate, a property that a thing can either possess or lack. When people assert that God exists they are not saying that there is a God and he possesses the property of existence. If that were the case, then when people assert that God does not exist they would be saying that there is a God and he lacks the property of existence, i.e., they would be both affirming and denying God’s existence in the same breath. Rather, suggests Kant, to say that something exists is to say that the concept of that thing is exemplified in the world. Existence, then, is not a matter of a thing possessing a property, existence, but of a concept corresponding to something in the world.
To see this more clearly, suppose that we give a complete description of an object, of its size, its weight, its colour, etc. If we then add that the object exists, then in asserting that it exists we add nothing to the concept of the object. The object is the same whether it exists or not; it is the same size, the same weight, the same colour, etc. The fact that the object exists, that the concept is exemplified in the world, does not change anything about the concept. To assert that the object exists is to say something about the world, that it contains something that matches that concept; it is not to say anything about the object itself.
If Kant is correct in his view that existence is not a property of objects, then it is impossible to compare a God that exists to a God that does not. On Kant’s view a God that exists and a God that does not are qualitatively identical. A God that exists is omnipotent, omniscient, omnipresent, etc. A God that does not exist is omnipotent, omniscient, omnipresent, etc. Both are the same. If this is right, then Anselm’s claim that an existent God is greater than a non-existent God is false—neither is greater than the other—in which case the ontological argument fails.
Responses to Kant
Kant’s criticism of the ontological argument is widely accepted, but there have been a few dissenting voices. Some have insisted that asserting that an object exists can change the way that we conceive of it. If, having read about Socrates in the works of Plato, I discover that he is a real historical figure, i.e. that he exists, then this extra information will change the way that I think about him. Similarly, it is suggested, to say that God is not a mere figment of believers’ imaginations, but actually exists, is to add something to the concept of God. Perhaps, then, Anselm’s comparison between a God that exists and a God that does not is possible, and the ontological argument survives Kant’s criticism.
Whatever you make of the ontological argument, the other arguments for the existence of God are independent of it. The next of them is the first cause argument.