Anselm claims God is a necessary existence, because he is too great not to exist. He must exist both in intellectu and in reality in order to be truly great. It is a logical contradiction to claim that God does not exist, because he has the characteristic of necessary existence. Anselm’s argument was not a new one – In Psalm 14 we read, “The fool says in his heart, there is no God.” He uses the analogy of the painter. The painter can imagine what he wants to paint, but the painting does not truly exist until he paints it. In the same way, God cannot only exist in the mind.
Furthermore, Anselm uses God’s perfection to prove his existence as part of the ontological argument. God is the ultimate perfect, and to be truly perfect he must exist in both mind and reality. He can’t be perfect if he does not exist. He effectively defines God into existence. If this was applied in the world this would be absurd, a criticism Gaunilo picked up on. Gaunilo was a theist, but critical of the ontological argument. He argued that he could just as easily imagine the perfect holiday island, but that does not mean it exists in reality. Anselm countered his argument by asserting that an island is subjective in its perfection, but God is not. The exchange between the two is a good example of reductio ad absurdum – trying to reduce each other’s arguments to absurdity.
Moving on, another philosopher that used the ontological argument was Descartes. Descartes argued that God’s existence is part of his very nature as a perfect being. God cannot be separated from existence in the same way a triangle can only have three sides, or else it ceases to be a triangle. He also argued that for him, an imperfect being, to be able to imagine God, a perfect being, must be the result of the perfect being implanting the ideas in his mind, because he would not be able to conceive of God on his own. His argument centres more on God’s necessary perfection than existence.
There are a few modern philosophers that have given their own slant on the ontological argument as well. These include Platinga and Malcom. Platinga argued the possible worlds theory: if there are any number of possible worlds, God must rationally exist on at least one of them. If God possess the qualities of maximum greatness and perfection on this world, he must logically possess these characteristics on all worlds. Our world is a possible world, so therefore God must exist. Malcom follows on and argues that God cannot be contingently existent (relying on something else), so he must be either necessary or impossible. We cannot say that God is totally impossible unless we have existed in all times and all places to verify that God is nowhere to be found. He is not impossible, therefore he must be necessary. If he is necessary, he exists.
To conclude, the ontological argument – when understood – is a very logical argument that continues to be used by scholars today. It may not be the most effective for convincing the atheist, but it serves its primary purpose of assuring the theist of their faith.