In a Sentences Commentary written about 1250 the Franciscan Richard Rufus subjects Anselm's argument for God's existence in his Proslogion to the most trenchant criticism since Gaunilon wrote his response on behalf of the "fool." Anselm's argument is subtle but sophistical, claims Rufus, because he fails to distinguish between signification and supposition. Rufus therefore offers five reformulations of the Anselmian argument, which we restate in modem formal logic and four of which we claim are valid, the fifth turning on a possible scribal error. Rufus's final conclusion is that the formulation in Proslogion, chapter 3, is convincing, but not that of chapter 2.