Kant on the Ontological Argument for the Existence of God: Why Conceivability Does Not Entail Real Possibility

In the ontological argument for the existence of God, Descartes famously argues that the idea of God is the idea of a perfect being. As such, the idea of God must combine all of the perfections. Now, as (necessary) existence is a perfection, God must exist. Leibniz criticized Descartes’ argument, pointing out that it rests upon the hidden assumption that God is possible. Leibniz argues, however, that God is really possible because realities cannot oppose one another, and so there could be no real opposition between the perfections. So, at least in the case of God, conceivability entails real possibility. Kant rejects this assumption and insists that the non-contradictoriness of an idea is not an adequate criterion for the real possibility of the object of the idea, for although predicates may be combined in thought to form a concept, this does not entail the properties they indicate may be so combined in reality. For this reason, Kant believes that it is impossible to prove the real possibility of God, and so the ontological argument is not sound. In this paper, I examine Kant’s reasons for reaching this conclusion. I pay particular attention to Kant’s argument in the Amphiboly, which deals with the concepts of agreement and opposition, and where Kant stresses the importance of the distinction between logical and real opposition. I will argue that this distinction plays a crucial role in Kant’s rejection of the ontological argument and rationalist Leibnizian–Wolffian metaphysics in general. I also show how Kant’s rejection of the possibility of what he calls the complete determination of a concept in the Ideal of Pure Reason, plays a role in his rejection of the conceivability entails real possibility principle.