
Although the question of God’s existence is a highly dubious one, J.L Mackie’s criticism of Anselm provides very a convincing counter-argument against the ontological assumptions he makes regarding the nature of existence and the ability to conceive the existence of a being which can or cannot exist.
Similarly to Gaunilo’s complaint that God is something which nothing greater can be conceived (according to Anselm’s argument from Proslogion 3) from its concept, Mackie argues that the existence of a being cannot be argued from the conceptual aspect of that being. Even if the supposition that God exists from a conceptual perspective, it does not follow necessarily that the existence (or existential realization) of such a being applies to the great-making properties which it conceptually possesses. In other words, if the supposition that existence was a greatness-making quality was accepted, the existence of such a being cannot be dually applied to the conception.
From this perspective it can be seen that Mackie is quite convincing. He illustrates the ontological weakness of Anselm’s argumentation: it cannot escape its own futility because it depends on “the impossibility of establishing some concrete reality on the basis of a mere definition or concept.” There is no such thing that falls under the concept of a not-really-existing being than which nothing greater can be conceived, because the existence of this concept is not realized. Even if the ‘fool’ can accept the greatness premise which is ingrained in the argument, it still fails because it is logically incoherent to claim that a being does not exist, while it still can be conceived in a conceptual fashion as a being which no greater can exist.
Lastly, it would be useful in mentioning that Anselm’s argument would be improved if the claim that God’s existence as a being which no greater being exists was not considered a self-evident one. Alternatively, the premise of greatness could be replaced with a stronger statement that the necessary existence of such a being would contribute to its perfection or greatness.
