Explain the Ontological Argument from Anselm's perspective.

St Anselm’s ontological argument is a deductive, priori, analytic argument which seeks to establish the existence of God by understanding the attributes of God in the sense of classic theism. Anselm wrote his Proslogion as a prayer originally, but it later became an argument for God by establishing his attributes. Anselm wrote his argument in two parts.

Anselm’s first part defined God as ‘that than which nothing greater can be conceived’ because if something greater existed, then that would be God, as God is a perfect being and can’t be improved upon. Anselm refers to the fool in Psalm 14:1 in his argument, ‘the fool said in his heart ‘there is no God.’ Anselm went on to say that fool understands God exists but he does not believe he exists. Anselm tries to disprove the fool by saying anyone who understands what is meant by God existing, must have a knowledge of him. Whatever is understood must exist even if a person chooses to dismiss it. Anselm points out the difference between an object in ‘ones understanding’ and to ‘understand’ that something exists. By using his definition of God, he argues that if God exists as a conceptual basis (in intellectu) then a greater being could exist both in mind and reality (in re). For example, if you are hungry, a real pizza is better than a fake one. There could be nothing greater than this being so it must exist and be called God. Anselm uses the logic of reductio ad absurdum which worked by proving the alternatives to God is absurd. Suppose God only exists in a person’s understanding, then God could be greater by existing in reality, meaning a greater God is possible, one which exists in reality.  

Part two of his argument looks at Gods existent being necessary (not dependant on anything else) rather than contingent (dependant on other factors).  Anselm started by suggesting that there is no possibility for God not to exist. He returned to his early definition of God, and suggested to be thought of as not existing would be inferior to thinking of something which must always exist. So therefore, Anselm concluded that God must necessarily exist.

Anselm argues that God exists because not only is God that than which nothing is greater can be conceived but he is a being with a necessary existence, if he were contingent, we’d imagine a necessary God. God is necessary and cannot not exist. This is the difference between the fool and the believer. The fool knows of ‘God’ but does not know God himself. Whereas the believer understands God is the ‘greatest being that can be conceived’ and he can’t be thought of as not existing.