Patristic/Medieval
Anselm of Canterbury
1033–1109
“That than which a greater cannot be conceived cannot exist in the understanding alone. For, suppose it exists in the understanding alone: then it can be conceived to exist in reality; which is greater.”
Anselm of Canterbury was a Benedictine monk who became archbishop under Norman rule. His presents the argument that God is "that than which nothing greater can be conceived," and that this concept already entails existence in reality. He proceeds from the meaning of the word God, inside prayer and confession, taking the concept itself as his ground. Gaunilo objected at once. Aquinas later refused the inference from concept to existence; Descartes revived a related form. The method is faith seeking understanding. Later philosophy of religion still answers him.
In the Conversation
1 of the Great Ideas