The story
Anselm of Canterbury (1033 to 1109) was an Italian-born monk and then prior of the abbey of Bec in Normandy when he wrote the Proslogion in 1077 to 1078. His biographer Eadmer says the argument came to him after long sleepless effort, during the night office of prayers. He defines God as that than which nothing greater can be conceived. Even a fool who says in his heart that there is no God understands this phrase, so God exists in his understanding. But a being that exists only in the mind is less than one that also exists in reality. If God existed only in the mind, we could conceive of something greater, which contradicts the definition. So God must exist in reality.
A fellow monk, Gaunilo of Marmoutiers, objected that one could use the same reasoning to prove the existence of a perfect lost island. Anselm replied that the argument works only for a being than which none greater can be conceived, not for an island, whose perfection can always be exceeded. The label ontological argument, meaning an argument from the concept of being, was attached much later, by Kant.
Aquinas rejected the argument, saying we cannot know God's essence well enough to infer existence. Descartes revived a version in 1641, Leibniz repaired it, and Kant objected that existence is not a property that makes a thing greater. In the twentieth century, Kurt Gödel wrote a modal version, and Alvin Plantinga defended another.
Why it mattered
- It started the long tradition of arguments from the idea of God, taken up by Descartes, Leibniz and modern logicians.
- Kant's reply that existence is not a predicate became a landmark in modern philosophy.
- It marks the revival of rigorous argument in Latin theology that led to scholasticism.
Sources
- Anselm of Canterbury Stanford Encyclopedia of Philosophy
- Ontological Arguments Stanford Encyclopedia of Philosophy
- Ontological argument Britannica
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