Ironically the most notable critique of the Ontological Argument for God’s Existence comes from a theist. For Kant the argument represents a categorical error of sorts. Kant’s criticism calls “existence” into question. Kant refuted the way in which “existence” was used by Anselm in the form of a real predicate that contributed to the existence of a being. Recall, for Anselm the argument was made that a being that existed in mind only was inferior to a being that existed in mind and reality. Thus Anselm’s argument required for “existence” to be a real predicate.
Allow me to attempt at an illustration. On my desk before me sits a mug of Kona coffee that I find to have a slight to moderate floral aromatic with a fruity character. However, I can recall waking up this morning thinking about a cup of Kona coffee with these same qualities the exception being existence of course because it is only conceived of in my mind. The question is, would the former coffee be superior to the latter because it has one more quality that the latter coffee doesn’t have, namely “existence”? In other words, can we treat qualities such as “floral aromatics” and “fruity character” the same way we treat “existence” as if it is a real predicate? Kant says we kant.
Being is evidently not a real predicate, that is, a conception of something which is added to the conception of some other thing.2
“Being is not a real predicate.” In the same way that existence adds nothing to the qualities of my coffee, so does existence add no other qualities to God. Rather what Kant would say is that the concept of existence is now being exemplified in my coffee or God. If being is not a real predicate, then Anselm’s argument is negated. At least that is what Kant is maintaining. There have been refutations of Anselm’s claim and some who even defend the idea that existence IS a real predicate. This however is a brief explanation of Kant’s argument and any further arguments might be forthcoming.
1 Immanuel Kant (1724-1804) is one of the most influential philosophers in the history of Western philosophy. His contributions to metaphysics, epistemology, ethics, and aesthetics have had a profound impact on almost every philosophical movement that followed him.
2 Immanuel Kant, The Critique of Pure Reason, tr. By J.M.D. Meiklejohn, in: Great Books in the Western World, vol. 42, Robert Maynard Hutchins edition in chief, Chicago, London, Toronto, Encyclopedia Britannica Inc., 1952, Transcendental Doctrine of Elements,pp.181.