Gaunilo of Marmoutiers - The "Lost Island" Refutation

The "Lost Island" Refutation

Anselm claimed his ontological argument as proof of the existence of God, whom he described as that being for which no greater can be conceived. A god that does not exist cannot be that than which no greater can be conceived, as existence would make it greater. Thus, according to St. Anselm, the concept of God necessarily entails His existence. He denies Gaunilo a Godless epistemology.

Gaunilo criticised Anselm's argument by employing the same reasoning, via reductio ad absurdum, to "prove" the existence of the mythical "Lost Island", the greatest or most perfect island conceivable: if the island of which we are thinking does not exist, it cannot be the greatest conceivable island, for, to be the greatest conceivable island, it would have to exist, as any existent island would be greater than an imaginary one. This, of course, 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, it must, by Anselm's way of thinking, exist. While this argument is absurd, Gaunilo claims that it is no more so than Anselm's.

Philosophers often attempt to prove the ontological argument wrong by comparing Anselm's with Gaunilo's. The former runs thus:

1. God is that being than which no greater can be conceived.
2. It is greater to exist in reality than merely as an idea.
3. If God does not exist, we can conceive of an even greater being, id est one that does exist.
4. Therefore, God must indeed exist in reality.
5. Therefore, He exists.

Gaunilo's argument runs along the same lines:

1. The Lost Island is that than which no greater can be conceived.
2. It is greater to exist in reality than merely as an idea.
3. If the Lost Island does not exist, one can conceive of an even greater island, id est one that does exist.
4. Therefore, the Lost Island exists in reality.

If one of these arguments is sound, it has been asserted, they must both be sound. By Gaunilo's reckoning, however, one (and, therefore, the other, too) is unsound. The Lost Island does not exist, so there is something wrong with the logic that proves that it does. Because the argument proves true in one case that which is patently false (the Lost Island), it is fair to ask whether it may fairly be regarded as proving true the other case. The fact that there is no perfect island is put forth by Gaunilo as showing that Anselm's argument for God's existence is flawed.

Such objections are called overload objections: they do not claim to show where or how the argument goes wrong; they merely argue that, if it is unsound in one application, it is unsound in all others. Simply put, they are arguments that would overload the world with an indefinitely large number of things, like perfect islands.