The Life of the Mind by Hannah Arendt

far-reaching, and even perhaps quite other, than those he himself recognized. 83 (While discussing Plato, he once remarked "that it is by no means unusual, upon comparing the thoughts which an author has expressed in regard to his subject ... to find that we understand him better than he has understood himself. As he has not sufficiently determined his concept, he has sometimes spoken, or even thought, in opposition to his own intention." 84 And this is of course applicable to his own work.) Although he insisted on the inability of reason to arrive at knowledge, especially with respect to God, Freedom, and Immortality—to him the highest objects of thought—he could not part altogether with the conviction that the final aim of thinking, as of knowledge, is truth and cognition; he thus uses, throughout the Critiques, the term
Vemunfterkenntnis
, "knowledge arising out of pure reason," 85 a notion that ought to have been a contradiction in terms for him. He never became fully aware of having liberated reason and thinking, of having justified this faculty and its activity even though they could not boast of any "positive" results. As we have seen, he stated that he had "found it necessary to deny
knowledge
...to make room for
faith," 86
but all he had "denied" was knowledge of things that are unknowable, and he had not made room for faith but for thought. He believed that he had built the foundations of a future "systematic metaphysic" as "a bequest to posterity," 87 and it is true that without Kant's unshackling of speculative thought the rise of German idealism and its metaphysical systems would hardly have been possible. But the new brand of philosophers—Fichte, Schelling, Hegel—would scarcely have pleased Kant. Liberated by Kant from the old school dogmatism and its sterile exercises, encouraged by him to indulge in speculative thinking, they actually took their cue from Descartes, went hunting for certainty, blurred once again the distinguishing line between thought and knowledge, and believed in all earnest that the results of their speculations possessed the same kind of validity as the results of cognitive processes.
    What undermined Kant's greatest discovery, the distinction between knowledge, which uses thinking as a means to an end, and thinking itself as it arises out of "the very nature of our reason" and is done for its own sake, was that he constantly compared the two with each other. Only if truth (in Kant, intuition), and not meaning, is the ultimate criterion of man's mental activities does it make sense in this context to speak of deception and illusion at all. "It is impossible," he says, that reason, "this highest tribunal of all the rights and claims of speculation should itself be the source of deceptions and illusions." 88 He is right, but only because reason as the faculty of speculative thought does not move in the world of appearances and hence can produce non-sense and meaninglessness but neither illusion nor deception, which properly belong to the realm of sense perception and common-sense reasoning. He recognizes this himself when he calls the ideas of pure reason only "heuristic," not "ostensive" concepts; 89 they are tentative—they do not demonstrate or show anything. "They ought not to be assumed as existing in themselves, but only as having the reality of a schema...[and] should be regarded only as analoga of real things, not as in themselves real things." 90 In other words, they neither reach nor are able to present and represent reality. It is not merely the other-worldly transcendent things that they can never reach; the realness given by the senses playing together, kept in tune by common sense, and that is guaranteed by the fact of plurality—is beyond their grasp. But Kant does not insist on this side of the matter, because he is afraid that his ideas might then turn out to be "empty thought-things" (
leere Gedankendinge
) 91 —as indeed they invariably do