Anselm's version of the ontological argument, is perhaps the most famous and arises in, "The Proslogion." Anselm deduces the existence of God, from the concept of God, and therefore his argument is a priori. .
"Proslogion Two," states, "God is that than which nothing greater can be conceived," even the fool, whom Anselm is trying to refute, must have an understanding of the idea God according to Anselm. The fool, "who says in his heart there is no God," (Psalms 14:1) has, "Two important features; he understands the claim that God exists. He does not believe that God exists." However, if the fool accepts the classical theism definition of the God, Anselm believes, "that which exists in reality will always be greater than that which exists purely in intellect." God is, "nothing greater can be conceived," it would not be using reason to then say, that he does not exist. To aid this, Peter Vardy gave the example of an envelope containing £1000. This envelope would evidently be better in reality, rather than simply in our minds, which Anselm believes to also be true of God. This leads to the second part of Anselm's argument, in, "Proslogion 3," and 5 that conclude if it is possible to conceive of a being whose existence is necessary, God must be such a being. If he truly is, "that than which nothing greater can be conceived." Anselm also states, "a being that possesses necessary existence will always be greater than a contingent being," such as ourselves.
The relationship between reason and faith, can bring up difficulties for some believers. However, Anselm was a strong believer in God, and wrote his argument in the form of a prayer to God. He believed we should use our faith, and belief in God in order to truly be able to use reason and understanding, when speaking about God. Anselm believes if we apply logic to the statement, "God is that than which nothing greater can be conceived," anyone would see that God must logically, and necessarily exist.
