In the first period he accepted the rationalism of Wolff, but his main interest, as shown by his writings, was in natural science. He was inspired by the natural philosophy of Newton, which, in the latter part of this period, led him to mistrust the metaphysics of Wolff. That is to say, he began to suspect that the mere logical operation of concepts by the “pure reason” could not be a statement about things in the real world. In the next ten years――his second period――he became convinced that the metaphysics of the rationalists was impossible, and yet that the metaphysics of the empirical school of the English was equally absurd. His writings during this time are more strictly devoted to questions of metaphysics and epistemology. Then came his critical period. This was inaugurated by his celebrated Dissertation of 1770, followed by a period of eleven years of literary silence, a silence broken by the publication of his _Critique of Pure Reason_ in 1781. Between 1781 and 1790 appeared the more mature works from Kant’s pen. Among them were the _Critique of Practical Reason_ (1788) and the _Critique of Judgment_ (1790), formed on the model of the _Critique of Pure Reason_. Besides these, his minor writings were very numerous, and one notes an essay by him in the last year of his life. But the writings of Kant after 1790 treat in the main of the philosophy of law and conduct, and show themselves to be the writings of his declining years. =The Problem of Kant.= The problem which Kant placed before himself was that of epistemology. Epistemology is the theory of knowledge, and Kant set to work to investigate the knowing process. The peculiar significance of Kant rests upon the fact that out of the various influences converging upon him and his time he matured a new conception of the problem and of the method of procedure of philosophy. He was convinced that the problem of his time was not one of metaphysical speculation, although he felt the value of such speculation in the regions of religion and morals. Yet he saw that the metaphysical rationalism of Wolff had proved itself inadequate because it was merely the logical operation of concepts, and had not dealt with real relations. He was equally sure that the empirical metaphysics of the Englishmen was inadequate because it was never certain of any truth. Rational metaphysics was logically true, but not real; empirical metaphysics was real enough, but never true. So Kant determined to find out the relation between the logical process of thought and the reality of things. He felt that the first problem in his time to be faced and settled was the problem of knowledge,――the epistemological problem. He planned to face later the metaphysical problem, but he delayed this until too late in his old age. The problem of Kant can be put in the simple question, What can we know? The metaphysical problem that he deferred was, What is real? Yet his problem was not nearly so simple as