How Medieval Philosophers Attempted to Prove the Existence of a God

Historical analysis and comparison of theories from St. Anselm and Ibn-Sina

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St. Anselm

“Even the fool is forced to agree that [something god-like] exists in his mind, since he understands this when he hears it, and whatever is understood is in the mind. And surely that [something god-like] cannot exist in the mind alone.”

In this passage, Anselm is claiming that it is a truth — by definition — that God is the highest being imaginable and that the notion of an all-powerful, all-knowing deity exists as an idea in our minds. Anselm continues his proof:

“Suppose it exists in the mind alone: then it can be conceived to exist in reality; which is greater…Therefore, if that [something god-like] exists in the understanding alone, the very being, [something god-like], is one that which a greater can be conceived. But obviously this is impossible. Hence, there is no doubt that there exists a being, [something god-like], and it exists both in the understanding and in reality.”

Put this way, Anselm’s claim makes sense: a being that exists as an idea in mind and also exists as an idea, in reality, is inherently higher than a person that exists only as an idea. Therefore, the argument states that if God only exists as an idea, then our imaginations can think of something greater than god. However, this is contradictory to the fundamental concept of God, who, by nature, is all-powerful and is the greatest. Therefore, according to Anselm’s ontological argument, God exists.

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Avicenna

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