The modal unity of anselm's proslogion

Anselm claimed that his Proslogion was a "single argument" sufficient to prove "that God truly exists," that God is "the supreme good requiring nothing else," as well as to prove "whatever we believe regarding the divine Being." In this paper we show how Anselm's argument in the Proslogion and in his Reply to Gaunilo can be reconstructed as a single argument. A logically elegant result is that the various stages of Anselm's argument are validated by standard axioms from contemporary modal logic.