Since the first Critique had argued that pure reason could not prove the freedom of the will, and since, in Kant’s view, morality required such freedom, the operations of reason seemed to have left morality, like theology, without a rational basis. Worse yet, the Enlightenment had sapped the religious foundation of morals by questioning the existence of a rewarding and punishing God. How could civilization survive if these traditional supports of morality collapsed? Kant felt that he himself, as an avowed disciple of the Aufklärung, was obligated to find some rational ground for a moral code. In a preliminary essay, Fundamental Principles of the Metaphysics of Morals (Grundlegung zur Metaphysik der Sitten, 1785), he rejected the attempt of freethinkers to base morality upon the experience of the individual or the race; such an a posteriori derivation would deprive moral principles of that universality and absoluteness which, in his judgment, a sound ethic required. With characteristic self-confidence he announced: “It is clear that all moral conceptions have their seat and origin completely a priori in the reason.”39 His second major work, Kritik der praktischen Vernunft, proposed to find and elucidate that seat and origin. It would analyze the a priori elements in morality as the firstCritique had analyzed the a priori elements in knowledge.

Every individual (Kant argues) has a conscience, a sense of duty, a consciousness of a commanding moral law. “Two things fill the mind with ever new and increasing admiration and awe … : the starry heavens above, and the moral law within.”40 This moral consciousness often conflicts with our sensual desires, but we recognize that it is a higher element in us than the pursuit of pleasure. It is not the product of experience, it is a part of our inherent psychological structure, like the categories; it is an internal tribunal present in every person in every race.41 And it is absolute; it commands us unconditionally, without exception or excuse, to do the right for its own sake, as an end in itself, not as a means to happiness or reward or some other good. Its imperative is categorical.

That categorical imperative takes two forms. “Act so that the maxim of thy will can always hold good as a principle of universal legislation”; act in such a way that if all others should act like you, everything would be well; this [variation of the Golden Rule] is the “fundamental law of the pure practical reason,”42 and is “the formula of an absolutely good will.”43 In a second formulation, “So act as to treat humanity, whether in thine own person or in that of any other, in every case as an end, never only as a means,”44Kant proclaimed a principle more revolutionary than anything in the American or French declaration of the rights of man.

The sense of moral obligation is additional evidence for some freedom of the will. How could we have this consciousness of duty if we were not free to do or not to do, if our actions were merely links in an unbreakable chain of mechanical cause and effect? Without free will personality is meaningless; if personality is meaningless, so is life; and if life is meaningless, so is the universe.45 Kant recognizes the apparently inescapable logic of determinism; and how can a free choice intervene in an objective world which (he confesses) is apparently governed by mechanical laws?46 His reply is a masterpiece of obscurity. Mechanical law, he reminds us, is a mental construct, a scheme which the mind, through its category of causality, imposes upon the world of space and time as a device for dealing with it consistently. Since we have limited the categories to the world of phenomena, and since we have admitted that we do not know the nature of the noumenal world—the thing-in-itself behind the phenomena—we cannot assume that the laws which we construct for the phenomena hold also for the ultimate reality. And as we have admitted that we know, in ourselves, only the phenomenal self—only the world of perceptions and ideas—and do not know the nature of the inner and noumenal soul, we cannot assume that the laws of cause and effect that seem to govern the actions of our bodies (including our brains) apply also to the volitions of the ultimate spiritual reality behind our mental processes. Behind the mechanisms of the phenomenal world of space and of ideas in time there may be freedom in the spaceless and timeless noumenal world of ultimate outer or inner reality. Our actions and ideas are determined once they enter the world of perceivable physical or mental events; they may still be free in their origin in the unperceivable soul; “in this way freedom and nature … can exist together.”47 We cannot prove this, but we may legitimately assume it as implied by the imperative character of our moral sense; our moral life would die without it.

After all (says Kant), why should we not give primacy to the practical over the speculative reason? Science, which seems to reduce us to automata, is ultimately a speculation—a gamble on the permanent validity of conclusions and methods that are always changing. We are justified in feeling that the will in man is more basic than the intellect; the intellect is an instrument forged by the will for dealing with the external and mechanical world; it should not be the master of the personality that uses it.48

But if the moral sense warrants us in assuming a measure of free will, it also warrants us in believing in the immortality of the soul. For our moral sense urges us on to a perfection that is repeatedly frustrated by our sensual impulses; we cannot achieve this perfection in our short earthly life; we must assume, if there is any justice in the world, that we shall be granted, for our moral fulfillment, a continued life after death. If this also assumes that a just God exists, this too is warranted by practical reason. Earthly happiness does not always accord with virtue; we feel that somewhere the balance between virtue and happiness will be restored; and this is possible only by supposing that there is a deity who will effect this reconciliation. “Accordingly the existence of a cause of all nature, distinct from nature itself, and containing the principle of … the exact harmony of happiness with morality, is also postulated” by the practical reason.49

Kant inverted the usual procedure: instead of deriving the moral sense and code from God (as the theologians had done), he deduced God from the moral sense. We must conceive our duties not as “arbitrary ordinances of a foreign will, but as essential laws of every free will in itself”; however, since that will and God both belong to the noumenal world, we should accept these duties as divine commands. “We shall not look upon [moral] actions as obligatory because they are commands of God, but we shall regard them as divine commands because we have an inward obligation to them.”50

If all this will-ful thinking is slightly obscure, it may be because Kant was not very enthusiastic about his attempt to reconcile Voltaire with Rousseau. The Critique of Pure Reason had gone even further than Voltaire in confessing that pure reason cannot prove free will, immortality, or God. But Kant had found in Rousseau’s doctrines—of the weakness of reason, the primacy of feeling, and the derivation of religion from man’s moral sense—a possible escape from agnosticism, moral disintegration, and Wollner’s police.He thought that Rousseau had awakened him from “dogmatic slumber” in ethics as Flume had done in metaphysics.51 The first Critique belonged to the Aufklärung; the second belonged to the Romantic movement; the attempt to combine both was one of the subtlest performances in the history of philosophy. Heine credited the attempt to solicitude for popular needs: the professor saw his faithful servant Lampe weeping over the death of God; “then Immanuel Kant had compassion, and showed himself not only a great philosopher but also a good man, and half kindly, half ironically he said: ‘Old Lampe must have a God, or he cannot be happy; … for my part the practical reason may, then, guarantee the existence of God.’”52

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