Gaunilo (fl. 11th century)
(fl. 11th century)
Soon after St. Anselm circulated his Proslogion, it was the target of a vigorous rejoinder by an otherwise unknown Benedictine monk named Gaunilo. Although Guanilo's "Reply on Behalf of the Fool" raises a number of objections to the ontological argument, by far the best known is the Lost Island reductio, an argument intended to be exactly parallel to Anselm's that generates an obviously absurd conclusion. Gaunilo proposes that instead of "that than which nothing greater can be thought" we consider "that island than which no greater can be thought" (2001, p. 31). We understand what that expression means, so (following Anselm's reasoning in the ontological argument) the greatest conceivable island exists in our understanding. But (again following Anselm's reasoning) that island must exist in reality as well; for if it did not, we could imagine a greater island—namely, one that existed in reality—and the greatest conceivable island would not be the greatest conceivable island after all. Surely, though, it is absurd to suppose that the greatest conceivable island actually exists in reality.
In order to defend himself against Gaunilo's criticism, Anselm would have to show why Gaunilo's argument about the island is not in fact analogous to his own argument about that than which nothing greater can be thought. Yet although his "reply to Guanilo" asserts more than once that the island example fails, he does not explain why it fails. The usual reply given on Anselm's behalf (and indeed often attributed to Anselm himself) is that the notion of a greatest conceivable island is incoherent; however great an island might be, one could always conceive of a greater. (For a reading of the argument that endorses a response of this sort, see Klima 2000.)
Gaunilo's reply does have its defenders, however, most notably Nicholas Wolterstorff, who argues that Anselm "realized the 'tellingness' of [Gaunilo's] points. … The sign of his realization, however, is not concession; Anselm does not concede. The sign is rather bluster" (Wolterstorff 1993, 87).
Gaunilo. "Reply on Behalf of the Fool." In Proslogion, with the Replies of Gaunilo and Anselm. Translated by Thomas Williams, 27–33. Indianapolis: Hackett, 2001.
Klima, Gyula. "Saint Anselm's Proof: A Problem of Reference, Intentional Identity and Mutual Understanding." In Medieval Philosophy and Modern Times, edited by G. Hintikka, 60–88. Dordrecht, Netherlands: Kluwer, 2000.
Wolterstorff, Nicholas. "In Defense of Gaunilo's Defense of the Fool." In Christian Perspectives on Religious Knowledge, edited by Stephen Evans and Merold Westphal, 87–111. Grand Rapids, MI: Eerdmans, 1993.
Thomas Williams (2005)