St. Anselm of Canterbury

Therefore, Lord, you have given understanding to faith, grant me that I may come to understand (as much as You think best) that You exist, as we believe, and that You are what we believe You to be. Now, we believe You to be a being than which none greater can be thought. Or is it possible that such a being does not exist, since the fool has said in his heart: there is no God (Ps. xiii)? And yet when that very fool hears what I am saying, namely, a being-than-which-none-greater-can-be-thought, he understands what he hears, and what he understands in his understanding — even if he does not understand that such a being exists. For it is one thing for a being to be in the understanding, and another thing to understand that a being exists. When a painter thinks over in advance what he is going to make, this is in his understanding; but he understands that what he has not made does yet exist. However, when he has painted it, he both has in his understanding what he has made and he also understands that it exists. — The Proslogion, Chapter II

St. Anselm of Canterbury (ca.1033–1109) was a Benedictine monk and one of the most influential theologians of the Middle Ages. He was archbishop of Canterbury (1093–1109) and known as the Father of Scholasticism chiefly due to The Proslogion, which presents the ontological argument (that is, based on reality or “being”) for the existence of God. In 1720 he was proclaimed a Doctor of the Church — a place of honor held by a select number of men and women who made significant contributions to the development of Church teachings.