Anselm's Ontological Argument

Anselm's Ontological Argument suggests that the very concept of a greatest, most perfect being—God—implies its existence. He reasons that if we can conceive of such a being, it must exist in reality because existing in reality is a greater perfection than existing only in the mind. If God existed only as an idea, then a greater being—one that exists both in the mind and in reality—could be imagined. Since that would be a contradiction, the argument concludes that God necessarily exists in reality, given the concept alone.