The classic ontological argument for the existence of God was put forward by Saint Anselm of Canterbury, a Benedictine monk, in the 11th century. It goes something like this: God is by definition an absolutely perfect being. We can’t conceive of any greater being. God has all the perfections—knowledge, goodness, power, and so on. But existence is a kind of perfection, too! An existing God is clearly greater than a nonexistent God. So if God doesn’t exist, he is imperfect. Since God is perfect by definition, God must exist!
