Gaunilo or Gaunillon (fl. 11th century) was a Benedictine monk of Marmoutier Abbey in Tours, France. He is best known for his contemporary criticism of the ontological argument for the existence of God which appeared in St Anselm's Proslogion. In his work In Behalf of the Fool, Gaunilo contends that St Anselm's ontological argument fails because logic of the same kind would force one to conclude many things exist which certainly do not. An empiricist, Gaunilo thought that the human intellect is only able to comprehend information provided by the senses.