We saw in the preceding chapter that the doctrine of illusion is central to Kant's theory of the intellect, or reason. At the heart of that theory is the view that reason is, by nature, constrained to seek knowledge that transcends any or all particular experiences, and that it seeks such knowledge by means of a system of ideas that provides a set of ultimate explanatory principles. Although these ideas are viewed by Kant as necessary, they also carry with them a certain unavoidable illusion. In line with this Kant claims that the conclusions drawn by the dogmatic metaphysicians in the specialized domains of rational psychology, cosmology, and theology are all based on a species of this illusion.

In this connection, it is crucial to keep in mind the distinction between the illusions and the fallacies of the Dialectic. Once again, Kant's position is that on the basis of an “unavoidable illusion” the metaphysician succumbs to formally fallacious reasoning or, what is for Kant correlated with this, to a transcendental misapplication of concepts. The fallacies of the Dialectic, however, are not unavoidable but flow (additionally) from the metaphysician's transcendental realism – that is, his failure to distinguish between appearances and things in themselves. Hence, in explicating these fallacies, I hope to show how Kant's doctrine of illusion provides the basis for, but is to be distinguished from, both transcendental realism and the faulty judgments and conclusions of dogmatic metaphysics.