The Ontological Argument is a philosophical reasoning that attempts to prove the existence of God through abstract concepts rather than empirical evidence. It suggests that if we can conceive of a perfect being, then that being must exist in reality, because existence is a necessary attribute of perfection. This argument was notably formulated by Anselm of Canterbury in the 11th century. He posited that the very definition of God as the greatest conceivable being implies that God must exist, as existing in reality is greater than existing only in the mind.