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...