That’s a mouthful! This is Anselm’s main point in his book, Proslogion. His defense for the existence of God has been a debated one since introduced in the 11th century. He was born in 1033 and forced to accept the position of Archbishop of Canterbury in 1093 (though reluctantly).
Anselm was a Realist in the Scholastic schools of the Roman Catholic Church – which is a school that aimed to show universal principles from the world that we live in. For example, one can see that God is intelligent from the order of Creation. God has purpose in Creation from the fact there is a food-chain, etc.
Proslogion is the sequel to his book, Monologion. In Monologion he attempted to show that God is ‘the best and greatest and highest of all things’. In Proslogion he attempts to show that God is ‘something-than-which-nothing-greater-can-be-thought’.
What does this mean? Think of a being that encapsulates the best of everything you can think of – justice, mercy, beauty, power, splendor, majesty. That which you think of is not God. Sorry. God is better than what you just thought of.
It might be argued that merely because you can think of something does not mean that it has to exist. For example, I can think of an beautiful island with white sandy beaches etc. That does not mean it has to exist. Response: This is true, it does not have to exist. However, to exist is greater than not to exist. Therefore, this island is not the greatest island because it does not exist.
In the same way, because existence is better than non-existence, God exists. Thinking of a being that is perfectly just, merciful, powerful, loving, etc. and for him to not exist means that this being is not ‘something-than-which-nothing-greater-can-be-thought’. Make sense?
Further, we know that there is such a being that exists because we have in our mind’s eye an understanding of what right and wrong is. That is, we have a sense of morality. The impossibility for morality to find its way through evolutionary processes of trial and error do not solve the problem of evil. We will get into this later in another discussion of God’s existence and the existence of morality – good and evil.
So before you leave this discussion, try this. Close your eyes and think of ‘something-than-which-nothing-greater-can-be-thought’. When you get to your highest thoughts, realize that God is more than this. And take comfort in the fact that existence is better than non-existence.
You can read more on this argument here .And I will also make it possible to download a three-page summary I wrote of the book that might be helpful.