His ethics is frequently called rigoristie, i.e. it refuses to recognize the moral value of natural inclinations. Nothing is good but the good will, and the good will is the will to do an act because it is in accordance with duty. "Duty is the obliga tion to act from reverence for law." The law is that "1 must net in sueh a way that I can at the same time will that my maxim should become a universal law." The obligation to obey this law is unconditional. The moral imperative is cate gorical. There are no ifs and bets in the ease. It does not even depend upon the peculiar 'con stitution of human nature. It is a necessary law for all rational beings, and as such a priori. "Its foundation is this, that rational nature exists as an end in itself." Man thus imposes upon him self the universal system of laws to which he is subject and "he is only under obligation to act in conformity with his own will." This constitut(s the autonomy of the will. But this autonomy is not correctly conceived unless correlated with the conception of a 'kingdom of ends.' i.e. 'the sys tematic combination of different rational beings Through the medium of common laws.' The au tonomy of any will is thus not capricious. but rational; its rationality consists in its ordered and systematic connection with other autonomous wills. "Morality, then, consists in the relation of all action to the system of laws which alone makes possible a kingdom of ends." This whole conception of the categorical imperative is pos sible, says Kant. only if man's will is not a mere phenomenon conditioned by causal laws. Free dom is thus a postulate of the moral order. We do not know ourselves to be free; for knowledge is possible only within the limit of experience. But we must think ourselves as free. "In think ing itself into the intelligible world, prac tical reason does not transcend its proper limits, as it would do if it tried to know itself directly by means of perception. In so thinking itself, reason merely conceives of itself negatively as not belonging to the world of sense." "There is but a single point in which it is positive. namely, in the thought that freedom. though it is a negative determination. is yet hound up with a positive faculty. and, indeed. with a causality of reason which is called will." This free causality of the will cannot he ex plained. for "we can explain nothing but that which we can reduce to laws, the object of which can he presented in a possible experience." "While. therefore, it is true that we cannot comprehend the practical unconditioned necessity of the moral imperative. it is also true that we can com prebend its incomprehensibility: and this is all that can fairly be demathled of a philosophy which seeks to reach the principles which deter mine the limits of human reason." But virtue or action in ar•ordance with duty, thonigh the su preme, is "not the or complete good which finite, rational beings desire to obtain. The com plete good includes happiness." This involves "the union of virtue and happiness in the same person." Put "the connection of virtue and happiness in a system of nature. which is merely an object of the senses, cannot be other than contingent. and therefore it cannot be established in the way re quired in the conception of the highest good." Snell a union is possible only if there is "perfect harmony of the disposition with the moral law," but of this harmony "no rational being existing in the world of sense is capable at any moment of his life." Yet "such a harmony must he possible. for it is implied in the command to promote that object ;" hence we most assume "an infinite prog ress toward perfeetharmony with the moral law," and this involves immortality as a. postulate of morality. But "the moral law leads us to postu late not only the immortality of the soul. but the existence of God," for there must ben cause "able to connect happiness and morality in exact har mony with each other," and God is the only con ceivable cause of this kind. Thu., the postulates of morality are God, freedom, and innnortality.
All this reasoning involves the assumption of two separate worlds—the world of sense. of phenom ena, and the world of intelligible but unknow able realities. But Kant was not content to rest in this absolute separation. Ile tries to bring these two worlds together. The beauty and the seeming purposiveness of nature make it probable that mechanism. the principle of the world of experience as governed by the conception of cause, and teleology. the principle of the world of intelligible realities as a kingdom of ends, are not. invompatible. They may be united in a single principle. which. however, because of the limitations of our reason, we cannot formulate.
It now remains to say something of Kant's place in the development of science. We have already seen that Kant's lectures were not con fined to philosophy. Indeed. his services in the theory of science were probably as great as in the realm of philosophy. It is only necessary to refer to Kant's anticipation of Laplace (q.v.) in the view that the solar system has developed from a primitive gaseous material with rotatory mo tion. Kant went further and suggested that the fixed stars might he systems. like the solar sys tem, which have arisen in the same way. This theory was worked out in the .111getnriar ur pcsehichte and Throrie des himmcl.s (l755), forty-four years before the appearance of the lh'renique or'Irstr (1799-1825).
In addition to the works mentioned by name above. Kant wrote nu hooks and essays, among the most important of which are the fol lowing: De Mundi Sensibilis (ague Intelliyibilis Forma et Prinripiis (17701: Prolegomena zu diner icdrn kiinftigen rtaphysik, die als Trissen sehaft •ird aaftrrica k6nnen (1783) Grandle gang zur Mrtapbysik der Rif ten (1785): Meta physisrhe nfangsgrande (•r Naturwissensrhaft ( 1786) ; AMU; der p•aktis•hca l'ernunit (1788); Kritik der rrtheilskraft (1790) (these last two works, together with the Kriti• der reinen rer nunft, contain the gist of Kant's whole philos ophy) ; Die Religion inmThalb der Grenzen der blossen lernunit (1793): Metaphysik der Silica (1797). In addition there arc works on physical geography. neural pathology. :esthetics, ethnog raphy. anthropology, history, criticism, meteorol ogy, polities, logic. and pedagogy. Ilis complete works Were edited by llopenkranz and Schubert (1838.42) ; by llortenstein (1867-69) ; and by Kirchmann. Among English translations of Kant's works mention should he made of the Critique of Pure Reason, trans. by Aleikle joint (London. 1854), and by Max Mailer (2d ed.. lb.. 189)) Profegontene, tr. by Malmify and Bernard (ib.,1889) ; Prolegomena and Metaphysical Foun dations of Natural Science, trans. by Bax (ib.. 1883) ; Critique of Practical Rcason and Oilier Works on th• Theory of Ethics, trails. by Abhott (ih.. 1898) ; Critique of Judgment, trans. by Ber nard (ib., 1892) : Philosophy of Laws, trans. by. Ilastie I Edinburgh. 1887) : Principles of Polities, trans. by Hastie (ih., 1891) ; Cosmogony, trans. by Tlastie (ib., 1900). A brief English version of Kant's philosophy is given in The Philosophy of Kant as Contained in Extracts from Ilis Olen Writings, selected and trans. by Watson (New York, 1894). Consult also: Mahatry. Kant's Critical Philosophy for English Readers (London. 1872-74) ; Watson, Kant and His English Critics (Glasgow, 18811: Stirling. Text-Rout,' to Kant (Edinburgh, 1881) ; Morris, Kant's Critique of Pure Reason (Chicago, 1882) ; Caird, Critical Philosophy of _Kant (New York. 1859) ; Paulsen, Immanuel Kant, scin Leben and seine Leh re (Stuttgart, 1808; Eng. trans.. New York, 1902) ; Vaihinger. Kommentar zur Kritik der reinen l'ernunft, of which two volumes have appeared (Leipzig, 1881.92). A bibliography. even very inadequate, of only the important works on Kant would take us beyond the limits of this work. Consult Adiekes, "Bibliography of Writings by Kant and on Kant which 11 are Appeared in Ger many Up to the End of 1887." in Philosophical Rericic (Boston. 1892 et seq.).