The empirical phase reaches its skeptical termination in the satire Dreams of a Ghost-seer explained by the Dreams of Metaphysics, 1766, which pours out its ingenious sarcasm impartially on spiritualism and on the assumed knowledge of the suprasensible.  Here Kant is already clearly conscious of his new problem, a theory of the limits of human reason, conscious also that the attack on this problem is to be begun by a discussion of the question of space.  This second question had been for many years a frequent subject of his reflections;[1] and it was this part of the general critical problem that first received definitive solution.  In the Latin dissertation On the Form and Principles of the Sensible and Intelligible World, 1770, which concludes the pre-critical period, and which was written on the occasion of his assumption of his chair as ordinary professor, the critique of sensibility, the new theory of space and time, is set forth in approximately the same form as in the Critique of Pure Reason, while the critique of the understanding and of reason, the theory of the categories and the Ideas and of the sphere of their validity, required for its completion the intellectual labor of several more years.  For this essay, De Mundi Sensibilis atque Intelligibilis Forma et Principiis, leaves unchallenged the possibility of a knowledge of things in themselves and of God, thus showing that its author has abandoned the skepticism maintained in the Dreams of a Ghost-seer, and has turned anew to dogmatic rationalism, whose final overthrow required another swing in the direction of skeptical empiricism.  In regard to the progress of this latter phase of opinion, the letters to M. Herz are almost the only, though not very valuable, source of information.

[Footnote 1:  New Theory of Motion and Rest, 1758; On the First Ground of the Distinction of Positions in Space, 1768; besides several of the works mentioned above.]

The Critique of Pure Reason appeared in 1781, much later than Kant had hoped when he began a work on “The Limits of Sensibility and Reason,” and a second, altered edition in 1787.[1] After the Prolegomena to every Future Metaphysic which may present itself as Science, 1783, had given a popular form to the critical doctrine of knowledge, it was followed by the critical philosophy of ethics in the Foundation of the Metaphysics of Ethics, 1785, and the Critique of Practical Reason, 1788; by the critical aesthetics and teleology in the Critique of Judgment, 1790; and by the critical philosophy of religion in Religion within the Limits of Reason Only, 1793[2] (consisting of four essays, of which the first, “Of Radical Evil,” had already appeared in the Berliner Monatsschrift in 1792).  The Metaphysical Elements of Natural Science, 1786, and the Metaphysics of Ethics, 1797 (in two parts, “Metaphysical Elements of the Theory