One of the first arguments made was by St. Anselm of Canterbury, a Christian philosopher, and theologian. Anselm said that if you are going to think about God, your mind obliges you to think about a being than which no greater can be thought of, this is known as the ontological argument. Ontology is the category of philosophical systems that deals with the nature of being, becoming, existence, or reality, as well as the basic categories of being and the relations between them all. This is an arguable idea when put in the context of theism because it is what you must think when you think about God and in itself does nothing in relation to the argument of whether or not God exists. This means that if someone was to think of the greatest possible meal, but in reality they ate out of a garbage can, what they ate out of the garbage can is greater than the meal that they had dreamed up because it is reality, and in Anselm’s idea, reality trumps non-reality, and so if God is supremely perfect, and the greatest possible thing, then He must exist since He cannot be greater than something that exists, if he does not. What Anselm is saying is that you must think of God as that which nothing greater can be thought of, or the supreme being. The major flaw in the ontological argument is that it assumes that God exists, or rather that one would have to assume that God exists.