The question of God's existence has occupied philosophers for centuries, yielding a diverse array of arguments. Among the most distinctive are the ontological arguments, which propose to demonstrate God's existence not through empirical observation or causal reasoning, but through the very concept of God itself. Primarily associated with Saint Anselm of Canterbury and René Descartes, these arguments posit that God’s existence is a necessary consequence of His definition. While elegantly conceived, the ontological argument faces significant philosophical challenges, particularly concerning the nature of existence as a property and the logical leap from concept to reality.
Anselm's formulation, presented in his Proslogion around 1078, defines God as "that than which nothing greater can be conceived." He argues that such a being must exist not only in the understanding but also in reality. If God existed solely in the understanding, then a greater being could be conceived – one that exists in reality. This, however, contradicts the initial definition. Therefore, God must exist in reality. Anselm’s reasoning hinges on the idea that existence in reality is intrinsically "greater" than existence merely in thought. This concept of "greatness" is central, implying that if we can conceive of a perfect being, that perfection must include existence.
René Descartes, in his Meditations on First Philosophy (1641), presented a similar argument. He claimed that existence is a perfection, and perfection is an essential attribute of God, just as having angles that sum to 180 degrees is essential to a triangle. Just as one cannot conceive of a triangle without its angles totaling 180 degrees, one cannot conceive of God without existence. For Descartes, the idea of a supremely perfect being inherently includes the attribute of existence. To doubt God's existence, he suggested, is as absurd as doubting that a mountain has a valley or that a winged horse lacks wings. The very concept of God, for him, contains the guarantee of His existence.
However, the ontological argument has faced persistent criticism. The most famous critique comes from Gaunilo, a monk contemporary to Anselm, who argued that one could use the same logic to prove the existence of a perfect island. Gaunilo contended that if we can conceive of a perfect island, and existence in reality is greater than existence in imagination, then this perfect island must exist. Since this conclusion is absurd, Gaunilo suggests, so too must be Anselm's original argument. Anselm responded by distinguishing between a necessary being (God) and a contingent one (the island), arguing that the logic applies only to that which is the greatest conceivable being, whose existence is a necessary attribute.
Later, Immanuel Kant, in his Critique of Pure Reason (1781), delivered a devastating blow to the ontological argument. Kant argued that "existence" is not a real predicate or perfection that can be added to the concept of a thing. Instead, he proposed that existence is merely the "position" of a concept with its object. When we say a thing "exists," we are not describing a new quality of that thing, but rather asserting that the concept corresponds to an object in the world. For example, the concept of a "hundred thalers" contains no more than the concept of a hundred thalers. When we say "a hundred thalers exist," we are positing the reality of those thalers, not adding a property called "existence" to the concept of thalers. Therefore, Kant concluded, existence cannot be a predicate that can be predicated of God, and thus the ontological argument fails.
Despite Kant's critique, the ontological argument continues to fascinate. Its enduring appeal lies in its attempt to establish God’s existence on purely rational grounds, independent of faith or sensory experience. It seeks to show that belief in God is not merely an option, but a logical necessity derived from the very definition of God. However, the fundamental problem remains: can we truly define something into existence? The transition from a conceptual analysis of "God" to a metaphysical claim about reality is a leap that many philosophers find philosophically unjustified. While the arguments of Anselm and Descartes are intellectually stimulating, they fail to surmount the philosophical hurdle that existence is not a property that can be logically deduced from a concept.