Kant’s revolutionary thinking, expressed in his magnum opus, “The Critique of Pure Reason”, allowed the debate to progress from its stalemate. Neither empiricist nor rationalist, Kant reminded the philosophical community of the subjectivity inherent in human experience. Hume conceded that our interpretation of sensory experience depended upon causal inference. But causal inference as a principle cannot be derived from experience, merely applied to it. Causal inference, then, is a presupposition that is necessary for experience as understood by a rational being.

Kant’s exploration of the presuppositions that shape our experience would seem, at first glance, to support the rationalist position: we have innate concepts and innate knowledge. But Kant affirms neither the rationalist nor the empiricist position. His own position is transcendental. To explain his thinking, he uses the analogy of a pair of spectacles. Our experience is like a man who sees the world through a pair of spectacles, but who lacks the ability to remove the spectacles. He knows that he is wearing spectacles, and from this infers that the spectacles are in some way influencing his vision. Now the external world may be very like the world of the spectacles, but he lacks the means of finding this out, because he cannot remove the spectacles. He must accept a limit to his knowledge (at least on an infallibilist understanding of knowledge); he must accept scepticism.

Kant’s exploration of the nature of experience is reminiscent of Descarte’s “evil demon” argument and of Berkeley’s idealism (more specifically his attack on the “material substratum”). Unlike the empiricists, he affirmed the existence of the synthetic a priori; however, unlike the rationalists, he denied that one could make an a priori argument for the existence of God. “God exists” is not an analytic proposition, but a synthetic one. A distinction must be made between two claims that are easily confused (for which reason, Kant would not be persuaded by Plantinga’s ontological argument).

A) “If God exists, then His existence is necessary.”

B) “God’s existence is necessary.”

To assert that God, by definition, is a being whose existence is not dependent upon any other entity is to make an analytic judgement. But the definition of a concept is distinct from the assertion that such an object exists. We may define UNICORN to our heart’s content, but that will not cause a unicorn to exist, nor does it depend on or presuppose the existence of a unicorn in the external world.

To assert that an entity exists or that something is the case is to make a synthetic judgement. Now, Kant has argued that some synthetic judgements are a priori (e.g. “2+7=9”). But can the proposition, “God exists”, be known this way? Is “God exists” a necessary truth? Maybe – but the ontological arguments of Anselm and Plantinga have not shown it to be so. The subjectivity inherent in the “spectacles” make our examination of both reason and experience problematic.

If we are to follow an empiricist method of arguing for the existence of God, then we must conclude that we cannot be certain of God’s existence (for which reason, faith is necessary). Experience does not provide us with universals, but only with matters of fact bound by the presuppositions of space in time imposed by us upon our experience through the spectacles.

If we attempt the path of reason, we will find that the Cartesian circle denies us certainty regarding the truth of “clear and distinct” ideas. The evil demon threatens.

The consequence of the empiricist and rationalist debates, and the Kantian progression beyond the debate, are scepticism and an awareness of human subjectivity. For that reason, faith is an essential ingredient in a person’s ability to grasp the proposition, “God exists.”