  Bonaventure’s ontological argument contains two moments, so to speak, one negative, the other positive. Negatively, Bonaventure’s ontological argument proceeds as a reduction to absurdity of the atheistic proposition. Anselm had taken a peculiar description of God, “something than which a greater cannot be thought,” which Augustine had used to argue through a reductio ad absurdum to the conclusion that God must be incorruptible, and Boethius used to argue that God must be good, and he had used it to argue by reductio that God must exist in the first place. Bonaventure recognized the affinity with arguing by reductio in support of the principle of non-contradiction: