Anselm’s ontological argument is an a priori proof of God’s existence. Anselm starts with an idea that depends on experience for their justification and then proceeds by purely logical means to the conclusion that God exists. His aim is to refute “the fool who says in his heart there is no God” (Psalms 14:1) this is showing that the ‘fool’ has important features which are; he understands the claim that God exists and he does not believe God exists. Anselm said “an atheist cannot consistently be an atheist”, they want to challenge that God does not exist but by having an understanding concept of God, then he must exist.
Anselm had a clear understanding of an all knowing, all powerful and an all loving God, thus believing God exists. The ontological argument describes God as “a being than which nothing greater can be conceived”, Anselm argued that the greatest possible being must exist otherwise he would not be the greatest possible being, although he must be the greatest possible being in every way including mind and reality. Anselm said atheists can define God even if they don’t believe in him. Rene Descartes said “I think therefore I am”, this means that if you can think about it you do exist, therefore if we think about God; he must exist.
God must have all perfections in order to be the greatest being; existence was perfection is better than existing in the mind rather in reality. Anselm’s a priori argument developed from his previous definition of God as “a being than which nothing greater can be conceived”, Anselm asked which is great: A God who can be thought of as not existing or A God who cannot be thought of as not existing. The answer has to be ‘A God who cannot be thought of as not existing’. So that, Anselm argued in his book Proslogion, proves logically that God’s existence is necessary. There is no doubt that there exists a being than which nothing greater can be conceived”, this is simply saying that no one can think of anything greater than God and therefore God is the greatest possible being. Anselm constructed an analytic argument; the definition of the subject necessarily includes the predicate just as in the earlier sentence about the widow. What is ‘the greatest possible being? ’ Well there is only one answer.
The same is true in this context if you ask ‘What is God? The answer has to be ‘the greatest possible being’, therefore another reason that supports Anselm’s ontological argument. In conclusion Anselm’s argument seems logical enough to have the evidence that God exists but only in our mind and not reality. But if you think about God in your mind then he must exist in reality. God is the greatest possible being and there is nothing greater than him, an atheist or the ‘fool’ can still think of God being all loving, all powerful and all knowing, therefore having a clear understanding of God and proving he exists.