St. Anselm (1033–1109), known as “Anselm of Canterbury,” was a Benedictine monk and the second Norman archbishop of Canterbury. He is famous for his ontological proof for the existence of God in Proslogion, and for his model of satisfaction in the Atonement in his Cur Deus homo.

Anselm’s ontological argument to prove God’s existence amounts to this: Imagine a being that is the greatest being that can be imagined. Such a being exists in the intellect alone. If this greatest being were to exist only in the intellect, a greater one that existed in reality could be imagined. But there cannot exist in reality a greater being than the greatest being that can be imagined. Therefore, that imagined being is the greatest being.

Now, this greatest being would be everything and have every attribute that it is better to have than not to have: living, wise, powerful, true, just, blessed, unchangeable, non-physical, eternal, beautiful, harmonious, sweet, and so forth. That is—and this is the crux of the ontological argument—because being is better than non-being, God will have being, which is to say, he will exist.

Anselm goes on to claim that God, as the greatest being that can be imagined, is simple. Everything that exists is better insofar as it more resembles the creator of all things: namely, God. All created beings, which are created by God, owe their being and well-being to God. But God is independent and has no obligations to his creations.