In 1764 he declined the offer of the chair of poetry at Königsberg; but soon after was appointed keeper of the royal library, with a modest salary. Kant was at last rewarded for the labours of these fifteen years in the way of all others most congenial to his taste. In 1770, after declining similar offers from Jena and Erlangen, he was elected to the chair of logic and metaphysics in the university of his native city. In his famous thesis, "De Mundi Sensibilis et Intelligibilis Forma et Principiis," published on this occasion, we at last find the germs of the critical philosophy afterwards delivered to the world in the great treatises of the latter part of his life, which were thus brought to maturity with a slowness of development fitted to encourage some and warn others.
The professorial epoch of Kant's life commenced in 1770, and his active labours as a professor extended over twenty-seven years. From 1770 to 1781, he published only one work, a programme of lectures on ethnography. In these eleven years, he was patiently working out a theory of human knowledge and life, which might be substituted for the hypothetical systems of the past, as a sufficient bulwark against the prevailing scepticism of the age of David Hume and the French encyclopedists. The question of the possibility of metaphysics, and of the necessary limits of the intellectual power of man, formed the great problem which he attempted to solve. The first part of his solution appeared in July, 1781, in the greatest of his works, the "Critique of Pure (or Speculative) Reason," which contains a review and reconstruction of the whole theory of human knowledge. The Essay of Locke and the "Critique" of Kant have been by far the most influential books in modern metaphysical literature. The same general problem is dealt with in each, by Locke with extraordinary good sense and practical intuition, and by Kant with unequalled subtilty and boldness. Each was a publication of the mature opinions of its author, for Locke and Kant were fifty-seven years of age when their greatest works were given to the world. But the point of view from which the Essay was written, was in many respects different from that of the "Critique." Locke in 1690 was struggling against the pedantic formalism and verbal disputations of the schools, as well as the civil and religious intolerance of his age, and his metaphysic was a reasoned protest on behalf of the duty of private judgment. Before Kant published his great work in 1781, the metaphysical dogmatism of Wolf had restored much of the empty notionalism which Locke, in conducting men's minds to nature and reality, sought to destroy; and, above all, the received assumptions and systems of the past had been shattered by the sceptical criticism which renders the publication of the philosophical works of David Hume, about 1740, the mark by which the later is separated from the earlier period in the history of modern philosophy. "I freely allow," says Kant, "that it was Hume's suggestion in his theory of causation that first awakened me from my many years of dogmatic slumber, and directed my speculative researches into a new quarter. I did not accept Hume's inferences, for I saw that he had drawn them from a partial and one-sided representation of the whole problem." The Scottish scepticism thus induced the reconstructive criticism of Germany, of which the first and most laboured instalment was produced, as has already been said, in 1781. The book was at the outset, as we might expect, misunderstood, and indeed like Hume's own Treatise on Human Nature, was at first in danger of falling still-born from the press. Kant accordingly in 1783 explained and popularized his design, in an introduction to his critical philosophy, entitled "Prolegomena to every Future System of Metaphysics Claiming to be a Science," which called forth much attention and controversy. A consequent demand for the second edition of the "Critique" was satisfied in 1787. The "Critique of Pure Reason" constitutes the fundamental part of the Kantian metaphysics; but it supplies only the foundation of the analysis even of speculative reason. It seeks to resolve the origin and abstract validity of the principles of knowledge, not the application of these principles to the knowledge of nature. A metaphysic of nature had still to be supplied. This Kant provided in 1786, in his "Metaphysical Elements of Physics," or an a priori analysis of the elements which constitute matter, by him explained under the conception of force, instead of by the old and traditional conceptions of solidity and impenetrability. This work is in some sort a supplement to the earlier metaphysic of Leibnitz, and an anticipation of the later philosophy of nature by Schelling. The years immediately following 1781 were also marked by several minor publications of Kant—in physics, the philosophy of history, and ethnology. It was not until 1788 that the second part of his great philosophical system was given to the world—the "Critique of Practical Reason," which forms the central part of his moral system, as the earlier "Critique" is of his purely speculative philosophy. The two are, in fact, correlative. While the analysis of reason, viewed as practical, implies a previous analysis of pure intelligence, the latter is incomplete and must be misunderstood if the results of the former are left out of account. Other works of Kant which appeared about this time should be compared with the second "Critique" in order to attain a comprehensive knowledge of his ethical system, and of the genius of his philosophy as a whole—in particular the "Groundwork of Ethics," published in 1785, which Mr. Semple's excellent translation has placed within the reach of English readers, as well as the "Metaphysical Elements of the Science of Law," and the "Metaphysical Elements of the Science of Morals," published about ten years later. The two last are related to the analysis of the practical, very much as the "Metaphysical Elements of Physics" are to that of the speculative reason. This group of Kant's writings supplies the keystone to his metaphysic arch. It embodies an ethical doctrine marked by a severe and almost unequalled grandeur, and resting on a basis that is absolute and eternal. In this highest part of his system, Kant's recognition of Duty as absolute virtually heals the wounds which his theory of Truth as merely relative, that is intertwined with its other parts, might seem to have inflicted, and restores that intercourse with reality which his previously demonstrated narrowness of human understanding appeared to forbid. After these two criticisms of Reason—in its relations to science, and in its relations to life and duty—had been completed, the third and last part of the philosophical edifice of Kant had still to be constructed. His first criticism analyzed man exclusively as intelligent—as related to knowledge and existence; his second, as also endowed with will—a responsible agent under law. It still remained to examine human nature as endowed with sensibility or feeling. This was attempted in the "Critique of Judgment" in 1790, which may be said to complete the Kantian system in describing its relations to æsthetics and natural theology. This work is divided into two parts; one of these analyzes our sensibilities to beauty and sublimity, and the fine arts; the other reviews the ends of nature, and contains a subjective theory of teleology. Before the last of the three "Critiques" was published, in 1790, the Kantian philosophy was beginning to produce a deep impression in Germany, notwithstanding the rigidly scientific phraseology in which it was given forth, and the originality of the course which its author had described for himself. Its doctrines were eagerly debated in the universities. The German intellectual world was divided into adversaries and partisans of Kant, and Königsberg was for the time the centre of interest to young Germany. The new system was at first much misunderstood. Some denied its claim to originality; others condemned it as a dangerous novelty, which subverted human belief in God and immortality, and dissolved real life in idealism. Mendelssohn, Feder, Tiedemann, Garve, Herder, the profound but mystical Jacobi, and many others, appeared as adverse critics. On the other hand, Kant was gradually surrounded by a numerous and powerful school, by whom his doctrines were zealously explained, defended, and applied to various parts of human knowledge. Schulze, Jacob, Beck, Buhle, Krug, Fries, Kiesewetter, Tennemann, and a host besides in different parts of Germany, developed various parts of the theory of man on the basis of Kantianism. Many of them were professors in the German universities, who thus spread the doctrines of their master by a powerful influence among the youth of the nation, with effects soon manifest in almost every part of literature and science. It was only by a later generation, at a time when Fichte, or even Schelling or Hegel, ruled the intellectual classes in Germany, that the Critical Philosophy gained a hearing among the intellectual classes in France and Great Britain. Nearly thirty years after the last of the three "Critiques" was published in Germany, the Kantian system was becoming known in France, through the clear and eloquent expositions of the great founder of its eclectic school , and although even before the close of last century and at the commencement of the present, outlines of Kant's system were given to the British public from London and Edinburgh, it was not until the first quarter of the century was passed that Kantianism began to influence our national thought—first through glimpses offered in the writings of Coleridge, and afterwards by
