Therefore, God might have been greater than he is. Therefore, God is NOT the being than which none greater is possible. Therefore, the being than which none greater is possible is NOT the being than which none greater is possible. Therefore, God exists in reality as well as in the understanding. Someone can conceive of X, but X does not exist.
Someone can conceive of X, and X exists.
With an introduction and brief commentary. From the Clemens and Alcuin Joint Libraries at St. John's University. Ontological Arguments A general discussion of the many forms that the ontological argument has taken, and various objections to each.