Anselm of Canterbury was the first to attempt an ontological argument for the existence of God, which is an attempt at an a priori proof for His existence. The following is Anselm’s argument:
- God is that than which nothing greater can be conceived.
- God may exist in the understanding.
- To exist in reality and in the understanding is greater than to exist in the understanding alone.
- Therefore, God exists in reality.
Frankly, this argument always annoyed me because I knew it was fallacious but couldn't really find the fallacy. In Bertrand Russel's words, "The argument does not, to a modern mind, seem very convincing, but it is easier to feel convinced that it must be fallacious than it is to find out precisely where the fallacy lies." The argument is simple and it has the facade of following logically from one step to the other, but as I will demonstrate it simply does not.
The fallacy behind this simple, concise little argument is a use-mention error in the second proposition (2). The use-mention error is a type of category error where you fail to make the distinction between the concept and that which the concept is referring. In the second proposition, Anselm is not talking about God (the alleged being), but "God" (the concept of the alleged being).
What Anselm did was try to demonstrate the existence of God through the existence of "God." They are in fact two separate things (which Anselm equivocates), and thus the argument does not follow.