Popular expositions have been given by the following: K. Fortlage (in his Philos. Vorträge, 1869); E. Last, Mehr Licht! Die Haupsätze Kants und Schopenhauers, 1879; the same, Die realistiche und die idealistische Anschauung entwickelt an Kants Idealität von Raum und Zeit, 1884; H. Romundt, Antaeus, neuer Aufbau der Lehre Kants über Seele, Freiheit, und Gott, 1882; the same, Grundlegung zur Reform der Philosophie, vereinfachte und erweiterte Darstellung von Kants Kritik der reinen Vernunft, 1885; the same, Die Vollendung des Socrates, Kants Grundlegung zur Reform der Sittenlehre; the same, Ein neuer Paulus, Kants Grundlegung zu einer sicheren Lehre von der Religion, 1886; the same, Die drei Fragen Kants, 1887; A. Krause, Populäre Darstellung von Kants Kritik der reinen Vernunft, 1881; K. Lasswitz, Die Lehre Kants von der Idealität des Raumes und der Zeit, 1883; Wilhelm Münz, Die Grundlagen der Kantischen Erkenntnisstheorie, 2d ed., 1885.
Among foreigners Villers, Cousin, Nolen, Desdouits, Cantoni, E. Caird [\A Critical Account of the Philosophy of Kant, 1877; The Critical Philosophy of Immanuel Kant, 2 vols., 1889], Adamson [On the Philosophy of Kant, 1879, and a valuable article in the Encyclopedia Britannica, 9th ed., vol. xiii.], Stirling [Text-book to Kant, 1881], [Watson, Kant and his English Critics, 1881], Morris Kant's Critique of Pure Reason, Griggs's Philosophical Classics, 1882, [Wallace, Kant, Blackwood's Philosophical Classics, 1882; Porter, Kant's Ethics, Griggs's Philosophical Classics, 1886; Green, Lectures, Works, vol. ii., 1886.—Tr.], have among others made contributions to Kantian literature. Of the older works we may mention the dictionaries of E. Schmid, 1788, and Mellin (in six volumes), 1797 seq., the critique of the Kantian philosophy in the first volume of Schopenhauer's chief work, 1819, and the essay of C.H. Weisse, In welchem Sinne hat sich die deutsche Philosophie jetzt wieder an Kant zu orientieren, 1847.
Kant's outward life was less eventful and less changeful than his philosophical development.[1] Born in Königsberg in 1724, the son of J.G. Cant, a saddler of Scottish descent, his home and school training were both strict and of a markedly religious type. He was educated at the university of his native city, and for nine years, from 1746 on, filled the place of a private tutor. In 1755 he became Docent, in 1770 ordinary professor in Königsberg, serving also for six years of this time as under-librarian. He seldom left his native city and never the province. The clearness which marked his extremely popular lectures on physical geography and anthropology was due to his diligent study of works of travel, and to an unusually acute gift of observation, which enabled him to draw from his surroundings a comprehensive knowledge of the world and of man. He ceased lecturing in 1797, and in 1804 old age ended a life which had always, even in minute detail, been governed by rule. A man of extreme devotion to duty, particularity, and love of truth, and an amiable, bright, and witty companion, Kant belongs to the acute rather than to the profound thinkers. Among his manifold endowments the tendency to combination and the faculty of intuition (as the Critique of Judgment especially shows) are present to a noticeable degree, yet not so markedly as the power of strict analysis and subtle discrimination. So that, although a mediating tendency is rightly regarded as the distinguishing characteristic of the Kantian thinking, it must also be remembered that synthesis is everywhere preceded by a mighty work of analysis, and that this still exerts its power even after the adjustment is complete. Thus Kant became the energetic defender of a qualitative view of the world in opposition to the quantitative view of Leibnitz, for which antitheses (e.g., sensation and thought, feeling and cognition, good and evil, duty and inclination) fade into mere differences of degree.
[Footnote 1: The following have done especially valuable service in the investigation of the development of Kant's doctrine: Paulsen (Versuch einer Entwickelungsgeschichte der Kantischen Erkenntnisstheorie, 1875), B. Erdmann, Vaihinger, and Windelband. Besides Hume and Leibnitz, Newton, Locke, Shaftesbury, Rousseau, and Wolff exercised an important influence on Kant.]
In the beginning of this chapter we have indicated how the new ideal of knowledge, under whose banner Kant brought about a reform of philosophy, grew out of the conflict between the rationalistic (dogmatic) and the empirical (skeptical) systems. This combines the Baconian ideal of the extension of knowledge with the Cartesian ideal of certainty in knowledge. It is synthetic judgments alone which extend knowledge, while analytic judgments are explicative merely.[1] A priori judgments alone are perfectly certain, absolutely universal, and necessarily valid; while a posteriori judgments are subjectively valid merely, lack necessity, and, at best, yield only relative universality.[2] All analytic judgments are a priori, all empirical or a posteriori judgments are synthetic. Between the two lies the object of Kant's search. Do synthetic judgments a priori exist, and how are they possible?
[Footnote 1: "All bodies are extended" is an analytic judgment; "all bodies possess weight," a synthetic judgment. The former explicates the concept of the subject by bringing into notice an idea already contained in it and belonging to the definition as a part thereof; it is based on the law of contradiction: an unextended body is a self-contradictory concept. The latter, on the contrary, goes beyond the concept of the subject and adds a predicate which had not been thought therein. It is experience which teaches us that weight is joined to matter, a fact which cannot be derived from the concept of matter. Almost all mathematical principles are synthetic, and here, as will be shown, it is not experience but "pure intuition" which permits us to go beyond the concept and add a new mark to it.]
[Footnote 2: The Scholastics applied the term a priori to knowledge from causes (from that which precedes), and a posteriori to knowledge from effects. Kant, following Leibnitz and Lambert, uses the terms to designate the antithesis, knowledge from reason and knowledge from experience. An a priori judgment is a judgment obtained without the aid of experience. When the principle from which it is derived is also independent of experience it is absolutely a priori, otherwise it is relatively a priori.]
Two sciences discuss the how, and a third the if of such judgments, which, at the same time, are ampliative and absolutely universal and necessary. The first two sciences are pure mathematics and pure natural science, of which the former is protected against doubt concerning its legitimacy by its evident character, and the latter, by the constant possibility of verification in experience; each, moreover, can point to the continuous course of its development. All this is absent in the third science, metaphysics, as science of the suprasensible, and to its great disadvantage. Experiential verification is in the nature of things denied to a presumptive knowledge of that which is beyond experience; it lacks evidence to such an extent that there is scarcely a principle to be found to which all metaphysicians assent, much less a metaphysical text-book to compare with Euclid; there is so little continuous advance that it is rather true that the later comers are likely to overthrow all that their predecessors have taught. In metaphysics, therefore, which, it must be confessed, is actual as a natural tendency, the question is not, as in the other two sciences, concerning the grounds of its legitimacy, but concerning this legitimacy itself. Mathematics and pure physics form synthetic judgments a priori, and metaphysics does the same. But the principles of the two former are unchallenged, while those of the third are not. In the former case the subject for investigation is, Whence this authority? in the latter case, Is she thus authorized?
Thus the main question, How are synthetic judgments a priori possible? divides into the subordinate questions, How is pure mathematics possible? How is pure natural science possible, and, How is metaphysics (in two senses: metaphysics in general, and metaphysics as science) possible? The Transcendental Aesthetic (the critique of sensibility or the faculty of intuition) answers the first of these questions; the Transcendental Analytic (the critique of the understanding), the second; and the Transcendental Dialectic (the critique of "reason" in the narrower sense) and the Transcendental Doctrine of Method (Methodenlehre), the third. The Analytic and the Dialectic are the two parts of the Transcendental "Logic" (critique of the faculty of thought), which, together with the Aesthetic, forms the Transcendental "Doctrine of Elements" (Elementarlehre), in contrast to the Doctrine of Method. The Critique of Pure Reason follows this scheme of subordinate division, while the Prolegomena co-ordinates all four parts in the manner first mentioned.
Let us anticipate the answers. Pure mathematics is possible, because there are pure or a priori intuitions (space and time), and pure natural science or the metaphysics of phenomena, because there are a priori concepts (categories) and principles of the pure understanding. Metaphysics as a presumptive science of the suprasensible has been possible in the form of unsuccessful attempts, because there are Ideas or concepts of reason which point beyond experience and look as though knowable objects were given through them; but as real science it is not possible, because the application of the categories is restricted to the limits of experience, while the objects thought through the Ideas cannot be sensuously given, and all assumed knowledge of them becomes involved in irresolvable contradictions (antinomies). On the other hand, a science is possible and necessary to teach the correct use of the categories, which may be applied to phenomena alone, and of the Ideas, which may be applied only to our knowledge of things (and our volition), and to determine the origin and the limits of our knowledge—that is to say, a transcendental philosophy. In regard to metaphysics (knowledge from pure reason), then, this is the conclusion reached: Rejection of transcendent metaphysics (that which goes beyond experience), recognition and development of immanent metaphysics (that which remains within the limits of possible experience). It is not possible as a metaphysic of things in themselves; it is possible as a metaphysic of nature (of the totality of phenomena), and as a metaphysic of knowledge (critique of reason).