It was slowly that Kant reached this conclusion, which became very prolific in his hands. He tells us that it was due to the examination of Hume's denial of any nexus between cause and effect, which of course re- duced the universe to a disconnected dream, and ren- dered all knowledge the mere aggregate of impressions fortuitously succeeding each other. He found that the same difficidty which had been exposed by Hume in re- gard to cause and effect existed in the case of all syn- thetic judgments « priori, or those which unite two un- connected conceptions in one proposition. Truth was thus deprived of all valiility, and experience became fallacy. How could a firm fomidation be attained? Was experience as hollow, and spectral, and delusive as it had been represented by Hume ? Three questions presented themselves for solution, each corresponding to a distinct branch of metaphysical inquiry : " What can I know?" "What ought I to do?" "What may I hope for?" The answer to the first question, which was the investigation of the nature of knowledge and of the na- ture of the mind, was given in the Critique of the Pure Reason. The answer to the second, wdiich embraced the theory of duty, was propounded in the Critique of the Practical Reason. The answer to the third, which con- templated the summum honum under a jieculiar aspect, was presented in the Critique of the Judf/mcnt — a very ambiguous designation. This distinction of subjects and division of treatises sprung from the distribution of the matter of philosophy then prevalent in Gemiany. The distribution had itself descended from Aristotle {^tioiu]- TiKi) yap Ktti TrpaKrtK}) Kai 7ron)TiK}) Xiyirai scil. t—i- a-rjf^tt]. — Top. vi, C ; comp. Metaph. v, 1 ; xi, 7 ; xii, 9).
(1) The Critique of the Pure Reason contains the es- sence of Kant's philosophy. It exhibits his method, illustrates his procedure, and presents his fundamentid conchisions. The conception of the Pure IJcason is in great measure his own, though both the name and what is denoted by the name are found in previous systems (Plotinus, Ennead. v, 3, 3; Leibnitz, Theod. § 1 ; Nouv. Ess. ii, iv, § 3). The pure reason is reason in its essential constitution — iv Cvvafiu, not iv ivtpyiia — the think-
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ing faculty in its adaptation to thought — erapty of the matter of thought, and distinct from its experiences. It is the mill witliout the grain which is to be ground by it. In analyzing the principle of thought, Kant detects an active as well as a passive factor. In every act of thought there is the reception of the impression from the object of thought, and the subjective reaction there- by excited, which reaction communicates the rational form to the conclusum, and differentiates to vovf^itvov, the subject of thought, from ro ^atvuyu£vo»', the object of thought.
Kant cUstinguishes the agencies which supply the materials of knowledge into three — sense, understand- ing, reason. The distribution of the faculties of the mind is always hazardous, and often beguiling. The mind is one and comjilcte. In the perceptions of sensa- tion, the elements derived from the mind, and not from the impression, are space and time. Such elements are called transcendental because they transcend, precede, and formulate the experience. They are consequently the forms or conditions of sensations. They are not supplied by the sensation, but they are added to it by the mind in the act of perception. There arc indica- tions of this doctrine in Plotiuus (^/mear?. ii, 7, 9), Leib- nitz (Nouv. Ess. liv. ii, chap, v), and in other writers. It is intimated, indeed, by Aristotle, and is a natural de- duction from the Ideas of Plato. It is singularly cor- roborated by recent expositions of the physiology of nervous action. In Kant's theory the phenomena of the external world are all sulyect to the conception of space, the phenomena of the mind to the conception of time. The sensationalist is thus refuted, as space and time are not obtained from sensation. The dogmatic idealist is refuted, as the matter of knowledge must be supplied by external impressions.
The understanding co-ordinates the perceptions of sense, and forms them into judgments by giving to them unity and interdependence. The transcendental elements supplied in this action of tlie understanding are arranged by Kant in twelve categories. The name of categories is taken from the Organon of Aristotle, but Kant's categories are entirely diverse from Aristotle's. Kant observed that metaphysical science pursued a de- lusive round, without making progress or securing sta- bility, while logic had received full, complete, and defi- nite form from its great founder. He ascribed this dif- ference of fortune to the fact that logic was simply the exposition of tlie procedure of the mind in reasoning, and he concluded that equal validity would be conferred on metaphysics, if it were reduced to an accurate repre- sentation of the procedure of the mind in the acquisition and employment of the materials of knowledge. Hence he invented a forced analogy between the two branches of speculation, and rendered his theory intricate, arbi- trary, and obscure by compelling it to assume a form fantastically corresponding with logical distinctions. In this spirit he devised his twelve categories, and ar- ranged them according to the forms of propositions, in the manner exhibited in the following table :