“My idealism concerns not the existence of things (the doubting of which, however, constitutes idealism in the ordinary sense), since it never came into my head to doubt it, but it concerns the sensuous representation of things, to which space and time especially belong.”
~Kant, Prolegomena to any Future Metaphysics (Remark III)
This passage from the Prolegomena explains Kant’s Transcendental Idealism, which is a counter-position to commonsense realism (but not a skepticism in the Cartesian sense) about the objects of perception. All appearances for Kant are neither “things in themselves” nor determinations from “things in themselves”. By “transcendental” Kant is creating a reference for our cognitive faculties from which we cannot justify any conversion of the appearances into actual things. The critical position that Kant takes refutes the positions of the “rational psychologists” and the “visionary idealists” who reify the objects of perception or convert actual things into mere representations, respectively. So far, Kant says, all of metaphysics has suffered from an enormous, yawning error, and Transcendental Idealism is the solution to all error theory.
This view of Kant’s must be evaluated on the whole, and contradistinguished from the various forms of idealism that are possible at least logically. Kant challenges reason and says we must be able to understand the limits of the transcendental, or critical, idealism, and judge the possibilities of transcendental idealism itself. We must consider the implications of this seriously.
Since Kant uses reason itself to judge the limits of reason, and since transcendental idealism limits what can be said about all appearances in the mind, in order to survive any fundamental critique of transcendental idealism, the theory must be able to justify itself without using any Archimedean levers grounded in appearances. Any Archimedean levers, references points used to move the rest of the world, cannot be left unjustified.
One theme of the Critique is a legal reasoning analogy that is employed in places where Kant discusses the importance of his work. Throughout the Critique we see that reason has been placed on trial. Yet throughout this trial reason is its own judge, its own jury, its own defense and the witness. To judge the limits of reason, therefore, we must call upon reason itself to bring us the verdict. The philosophical Justice System may also be fundamentally in error, an enormous, yawning error that Kant left unchallenged.
Such a thorny, unresolved paradox in Kant’s work should suggest that his work is purely an unjustified exercise in reason, or that one of its more basic points is that all knowledge is purely tautological. The second point is more interesting. It makes Kant’s work compatible with logic (the rules of the mind that reason follows), but since only compatible with reason, it judges the compatibility of this work by its own standards. Yet if reason is a mere representation in the mind, or the result of some natural drive or natural propensity to go on justifying itself, then we should rightly doubt the possibility of using reason as the Archimedean lever from which we can move the rest of the world.
Kant, Immanuel. Prolegomena to Any Future Metaphysics. Cambridge University Press, 2004: New York, NY.
Kant, Immanuel. Critique of Pure Reason. Translation by Norman Kemp Smith. Palgrave Macmillan, 2003: New York, NY.
Loeb, Paul. Lectures on Kantian Philosophy. University of Puget Sound, 2008: Tacoma, WA.
Van Cleve, James. Problems From Kant. Oxford University Press, 1999: New York, NY.