Descartes developed Anselm’s argument. His definition of God as a “supremely perfect being” is the basis of his argument. From this, Descartes believes we can conclude that God exists because existence is a predicate of a perfect being; Therefore, God must exist to avoid being self-contradictory. Descartes says that to imagine God without existence is like imagining a triangle without three sides.
Philosophers have also considered this argument in more recent times such as Norman Malcolm (necessary existence) and Alvin Plantinga (possible worlds). Iris Murdoch also pointed out that the ontological argument is not simply a piece of logic, but something that points to a spiritual reality that transcends any limited idea of God. However, this argument has also had its fair share of criticisms.
Gaunilo opposed Anselm, putting forward his own argument of the most perfect island. He said that if you were to believe this island must exist because of its perfection then you are a fool. By this, Gaunilo is trying to criticize the process by which Anselm moves from his definition of God to his suggestion of God’s existence.
Of course Gaunilo has a point: If the idea that a type of thing “than which no greater could be conceived” must necessarily exist, might this not apply to the most perfect potato or the greatest monkey? Aquinas says not, claiming that these are material things that go in and out of existence, unlike God.
However, Kant made a more successful criticism of Descartes’ version of the argument. He objected to Descartes claim that denying God’s existence is comparable to denying that a triangle has three sides. Kant offered the alternative of not having a triangle at all and therefore there are also no sides. He said that in the same way, if you don’t accept the concept of God in the first place, it is a useless argument.
Further criticism comes from the Empiricist David Hume. The foundation of his philosophy is that you must go outside a concept to determine whether it exists in reality. He says that a concept can only exist when they can be proved with the senses. He says of the ontological argument: “ We cannot define something into existence, even if it has all the perfections we can imagine.”
So, it would seem that someone who has no concept of God would not find this argument convincing, just as a religious believer will find that it confirms his or her faith. It would appear that mere definition is not enough. However, it would seem that Anselm was writing specifically for those already instilled with belief and had no intention of preaching to the unconverted: “I have written the following treatise in the person of one who seeks to understand what he believes.”
Therefore, it is evident that, despite some convincing elements within this argument, it only serves to strengthen a believer’s faith with no value for the non-believer. Final analysis would reveal that Kant’s criticism is probably the most accurate interpretation of this argument.
