Anselm Insisted His Critic's Reply Be Bound With His Own Book

Around 1077, while still prior at the Norman abbey of Bec, Anselm of Canterbury wrote the Proslogion — a short book containing what would become the ontological argument. God, he argued, is "that than which nothing greater can be conceived." If such a being existed only in the mind, you could conceive a greater one that also existed in reality, which is a contradiction. So the being must exist.

The argument irritated a Benedictine named Gaunilo, at Marmoutier Abbey near Tours. Within a year, he wrote a tract called Pro Insipiente — "On Behalf of the Fool," a reference to Psalm 14's atheist. His move was to substitute an island for God. Imagine the most perfect island conceivable, he said. By Anselm's logic, denying its existence is a contradiction, since a non-existent island would lack a property the most perfect island must have. The island doesn't exist; therefore something is wrong with the argument.

Anselm wrote a reply, the Responsio. He insisted Gaunilo's parody missed the point: the move only works for a being whose nature requires existence, and an island's doesn't. Whether that defense holds is still debated nine centuries later.

What is unusual is what Anselm did next. He directed that future copies of the Proslogion be bound with both Gaunilo's objection and his own reply, all three texts traveling together. Most medieval authors who answered critics did not preserve the critic's text. Anselm did. The Latin manuscript tradition obliged, and modern editions still print all three side by side.

The exchange became a template: an argument, an objection from a colleague who wasn't trying to be charitable, a reply, all kept legible. Gaunilo's tract survives only because Anselm wanted it to.