Explain the approach to proving the existence of God taken by Anselm’s ontological argument.

Anselm's Ontological argument, ontological meaning concerned with being or existence, makes an argument for the existence of God based not on a posteriori reasoning like other arguments for the existence of God, but rather on a priori reasoning, relying on a logical conclusion following a number of definitions. This argument is reliant on the acceptance of two definitions; that God is "that than which nothing greater can be imagined" and that things that exists are better than things that do not. The inductive leap from the first definition to the second is a reasonable, logical, progression, as proven in an example of the difference between £100 that doesn't exist, and £50 that does. In this scenario the £50 would be seen as the better option to take because it really exists and is useful in the real and practical world, just as a God that exists would indeed be better than a God that does not exist.For many people it is the first definition that they struggle with. Although Anselm refers to the fool (atheist) in Psalms to appeal to the fact that anyone can imagine "that than which nothing greater can be imagined", this does not mean that they have a belief in such a being. Definitions do not imply faith, and as such many people have taken issue with this assumption. Anselm, however, does make a point in this argument that his purpose is not to convert someone to a belief in God, but rather explain why it is necessary for the God he believes in to exist, and thus he would not have felt the need to make a point of proving an existence of the being he describes in the first definition. Therefore, perhaps Anselms argument should not be judged on it's ability to convert, but rather on it's logic from a point assuming that the first definition is already true.