Anselm

Anselm is famous for his ontological argument for the existence of God. An ontological argument for the existence of God argues that, by God’s very nature, He necessarily exists.

Ontological Argument

1. By definition, God is the greatest imaginable being.
2. Assume, for reductio, that God does not exist.
3. Then we can the imagine something exactly like God, call it Schmod, except that we imagine Schmod exists.
4. Something that exists is greater than something that does not exist.
5. So, Schmod is greater than God.
6. But that’s a contradiction since God is by definition the greatest imaginable being.
7. Hence, God exists.

Gaunilo's Objection

Gaunilo will show that Anselm’s argument is no good by showing that an exactly parallel argument gets us an absurd conclusion.

1. By definition, The Perfect Island is the greatest imaginable island.
2. Assume, for reductio, that The Perfect Island does not exist.
3. Then we can the imagine something exactly like The Perfect Island, call it The Perfect Island 2, except that we imagine The Perfect Island 2 exists.
4. Something that exists is greater than something that does not exist.
5. So, The Perfect Island 2 is greater than The Perfect Island.
6. But that’s a contradiction since The Perfect Island is by definition the greatest imaginable island.
7. Hence, The Perfect Island exists.

Have we now proven that the perfect island exists? Surely not! But if this argument does not work, then Anselm’s doesn’t, since they have exactly the same structure.