In 1078, Anselm of Bec wrote the most famous proof in Western religious tradition—what we know now as the "ontological argument" for God's existence. Stating that the "idea" and "reality" of God were the same, Anselm provoked enormous controversy through a radical approach: rather than appealing to the Bible, church authority, or the physical senses, he employed the faculties of his mind, crafting a method of logic that paved the way for modern thought.

Larry Witham traces our modern-day conceptions of faith and reason back to Anselm's formidable claim. In attempting to "prove God," Anselm unleashed a medieval debate that culminated in William of Ockham, whose notorious "razor" denied all such proofs, limiting knowledge to "things" only. Scrupulously managing fact and theory, Witham tells the story of this intellectual quest across the Middle Ages and how it inspired the West's "first modern philosopher," René Descartes.

By turns history, biography, and philosophical inquiry, The Proof of God follows one of the seminal arguments of Western belief from its inception to the present.