Gaunilo of Marmoutiers

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Gaunilo proposed a perfect island in his critique of Anselm's ontological argument

Gaunilo (or Gaunilon) of Marmoutiers was an 11th-century Benedictine monk, a contemporary of St. Anselm. He is primarily known for his criticism of Anselm's ontological argument for the existence of God, especially in his On Behalf of the Fool. Gaunilo's rebuttal of Anselm's argument gets its name from the fools of Psalm 14:1 and Psalm 53:1, who say in their hearts that there is no God, to whom Anselm refers as he develops the argument in his Proslogion. Unfortunately, little is known about Gaunilo and no other writings of him exist present day.

Anselm claimed to prove the existence of the greatest conceivable being, and he called that being God. A God that does not exist could not be that than which no greater can be conceived, because He could be imagined to exist, which would be greater. Therefore, according to St. Anselm, the concept of God necessarily entails His existence. Gaunilo criticised Anselm's argument by using the same reasoning to prove the existence of the greatest conceivable island. Gaunilo invited his readers to think of the greatest, or most perfect, conceivable island. As a matter of fact, it is likely that no such island actually exists. However, his argument would then say that we are not thinking of the greatest conceivable island, because the greatest conceivable island would exist, as well as having all those other desirable properties. Note that this is merely a direct application of Anselm's own premise that existence is a perfection. Since we can conceive of this greatest or most perfect conceivable island, then it must exist. While this argument seems absurd, Gaunilo claims that it is no more so than Anselm's. Philosophers can prove that the ontological argument is unsound by comparing both arguments. St Anselm's argument is as follows:

1. The Perfect Being (God) is defined as that than which nothing greater can be conceived
2. It is greater to exist in reality instead of merely as an idea
3. If the Perfect Being did not exist, then you could have an idea of an even greater being
4. So the Perfect Being must exist in reality (God exists).

Gaunilo's argument is as follows:

1. The Lost Island is defined as the greatest conceivable island
2. It is greater to exist in reality instead of merely as an idea
3. If the Lost Island did not exist, then you could have an idea of an even greater island, which did exist
4. So the Lost Island must exist in reality.

If any of these arguments are sound, it seems, they must all be sound. But, these arguments are not all sound; the perfect island cannot be found as it does not exist, and so there is something wrong with the logic of these arguments. Each of these arguments uses the same logic. They must therefore all be unsound. The fact that there is no perfect island shows that the logic of the ontological argument for God's existence is flawed. Such objections are known as "Overload Objections"; they do not claim to show where or how the ontological argument goes wrong, they simply argue that if it is sound, then so are many other arguments of the same logical form which we do not want to accept, arguments which would overload the world with an indefinitely large number of things like perfect islands, etc. Gaunilo's objection to the ontological argument was 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. St Anselm replied to Gaunilo's criticisms by arguing that the concept of 'that than which nothing greater can be conceived' cannot be applied to an island, or any other object, in the way in which he applied it to the definition of God. Anselm defends his proof by saying they only apply to God and not any other objects or beings. Also, a necessary being would be the greatest conceivable existence and qualify as the greatest of all possible beings. Only God exists necessarily. It seems that Gaunilo's criticisms against St. Anselm's version of the ontological argument were unsuccessful in ruling out this argument for the existence of God, although they certainly raised doubt about the logical structure of Anselm's proof.