It's Anselm not Anslem, and definitely not Aslan.... Anselm's Ontological Argument version 1 + 2

Fides Quarens Intellectum. Anselm was a man of faith, and wrote from a position of faith. Through this Faith Seeking Understanding he would have been writing to put across his Ontological Argument to other people of faith. And this possibly is the most important factor to remember about the argument, as he was starting from the Christian understanding of what the definition of God is. Something that Anselm sought to do with his argument was challenge the fool, who is written about in Psalms 14:1 and 53:1. In both instances it says "The fool says to himself" "there is no God".

Now the first thing to understand is the definition of God that Anselm uses for this ontological argument. For him, God is that than which nothing greater can be conceived (TTWNGCBC). So seeing as this was what Anselm's idea of God was, this also applied to what the Fools idea of God was. So in saying "there is no God" it would seem that the Fool has somewhat contradicted himself in the eyes of Anselm. Indeed as Anselm continues to explain, both existing in reality and in concept is far greater than just existing in concept alone. Which therefore follows that existence of any kind is a great attribute. And as God is that than which nothing greater can be conceived he must therefore fulfil his own definition of being the greatest by existing in both reality and in concept. So, going back to the Fool, it would seem that because he has an idea of God, he is presumably in understanding of the definition of God along with his idea. This is due to the fact that he cannot imagine something and then contest the idea without sharing the same definitions. So because he has an idea of God, by definition this God must exist, for as Anselm explains, God is that than which nothing greater can be conceived.                                                                Which means God exists!

However... Gaunilo had a different idea... For he gave an argument against Anselm's by giving the idea of replacing God with the an island of your dreams, or if you like, that than which no greater island can be conceived. And he seemed to prove Anselm's argument wrong for a while as he correctly said that just because he can imagine a perfect island does not mean that it will exist in reality. As well as this, Gaunilo also stated that "An object can hardly or never be conceived according to the word alone" as the word corresponds to an idea, and while the word may stay the same the idea behind it can be changed endlessly.

BUT! Anselm wasn't so easily proved wrong and came back with a more refined argument. In addition to that, he also reminded Gaunilo that anything that you apply to the island is going to be contingent, as they are all Earthly features, as opposed to attributes of God which are necessary, and cannot ever be understood fully by people. So in order for Anselm to refine it, he asked the question, which is greater; A God who can be though of as not existing? Or, A God who cannot be thought of as not existing? His answer was the second question, because it presents an idea of a God where it is impossible for God not to exist. Furthermore, not only is the second question a description of a greater God, but again a description of a necessary God, therefore proving Gods existence as necessary.