Liber apologeticus contra Gaunilonem

work by Anselm of Canterbury

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June 30, 2026

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The Liber apologeticus contra Gaunilonem (Apologetic Book Against Gaunilo) is a work by St. Anselm of Canterbury. It serves as a defense of his ontological argument for the existence of God.123

The ontological argument posits that the very concept of a being greater than which nothing can be conceived implies that being's existence. Gaunilo, a monk from Marmoutier Abbey, critiqued this argument in his Liber pro insipiente ("In Defense of the Fool"). He argued by analogy, suggesting that the concept of a "perfect island" does not guarantee its existence. Anselm's work is a response to Gaunilo's objections, further elaborating on the rationality of his assertion that God's existence is logically necessary.231

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St. Anselm of Canterbury
Early life and career
Anselm wrote in reply his Liber apologeticus contra Gaunilonem (“Book [of] Defense Against Gaunilo”), which was a repetition of the ontological argument of the Proslogion. The ontological argument was accepted in different forms by René Descartes and Benedict de Spinoza, though it was rejected by Immanuel Kant.
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Anselm wrote in reply his Liber apologeticus contra Gaunilonem (“Book [of] Defense Against Gaunilo”), which was a repetition of the ontological argument of the Proslogion. The ontological argument was accepted in different forms by René Descartes and Benedict de Spinoza, though it was rejected by Immanuel Kant.
Read More