Ancient Greek philosophy was divided into three sciences: physics, ethics, and logic. This division is perfectly suitable to the nature of the matter, and there is no need to amend it, except perhaps just to add its principle, partly so as to assure oneself in this way of its completeness, partly to be able to determine correctly the necessary subdivisions.

All rational cognition is either material and considers some object, or formal and occupied merely with the form of the understanding and of reason itself, and with the universal rules of thinking as such, regardless of differences among its objects. Formal philosophy is called logic, whereas material philosophy, which has to do with determinate objects and the laws to which they are subject, is once again twofold. For these laws are either laws of nature, or of freedom. The science of the first is called physics, that of the other is ethics; the former is also called doctrine of nature, the latter doctrine of morals.

If so far we have drawn our concept of duty from the common use of our practical reason, it is by no means to be inferred from this that we have treated it as an experiential concept. Rather, if we attend to our experience of the behavior of human beings we meet frequent and, as we ourselves concede, just complaints that no reliable example can be cited of the disposition to act from pure duty; that, though much may be done that conforms with what duty commands, still it is always doubtful whether it is actually done from duty and thus has a moral worth. That is why there have been philosophers in every age who have absolutely denied the actuality of this disposition in human actions, and attributed everything to a more or less refined self-love, without however calling into doubt the correctness of the concept of morality because of this; rather, with intimate regret they made mention of the frailty and impurity of a human nature that is indeed noble enough to take an idea so worthy of respect as its prescription, but at the same time too weak to follow it, and that uses reason, which should serve it for legislation, only to take care of the interest of inclinations, whether singly or, at most, in their greatest compatibility with one another.

In fact, it is absolutely impossible by means of experience to make out with complete certainty a single case in which the maxim of an action that otherwise conforms with duty did rest solely on moral grounds and on the representation of one’s duty. For at times it is indeed the case that with the acutest self-examination we find nothing whatsoever that – besides the moral ground of duty – could have been powerful enough to move us to this or that good action and so great a sacrifice; but from this it cannot be inferred with certainty that the real determining cause of the will was not actually a covert impulse of self-love under the mere pretense of that idea; for which we then gladly flatter ourselves with the false presumption of a nobler motive, whereas in fact we can never, even by the most strenuous examination, get entirely behind our covert incentives, because when moral worth is at issue what counts is not the actions, which one sees, but their inner principles, which one does not see.

A life devoted to the pursuit of philosophical inquiry may be inwardly as full of drama and event – of obstacle and overcoming, battle and victory, challenge and conquest – as that of any general, politician, or explorer, and yet be outwardly so quiet and routine as to defy biographical narration. Immanuel Kant was born in 1724 in Königsberg, East Prussia, to a Pietist family of modest means. Encouraged by his mother and the family pastor to pursue the career marked out by his intellectual gifts, Kant attended the University of Königsberg, and then worked for a time as a private tutor in the homes of various families in the neighborhood, while pursuing his researches in natural science. Later he got a position as a Privatdozent, an unsalaried lecturer who is paid by student fees, at the University. There Kant lectured on logic, metaphysics, ethics, geography, anthropology, mathematics, the foundations of natural science, and physics. In 1770, he finally obtained a regular professorship, the Chair of Logic and Metaphysics, at Königsberg. Destined by limited means and uneven health never to marry or travel, Kant remained in the Königsberg area, a quiet, hardworking scholar and teacher, until his death in 1804.

The translation of this new edition of Immanuel Kant’s Groundwork of the Metaphysics of Morals first appeared in my German–English edition (Cambridge, 2011). It is based on Mary Gregor’s English version, first published by Cambridge University Press in 1996 and subsequently reprinted in the Cambridge Texts in the History of Philosophy.

Throughout the revision process, care was taken to preserve the familiar feel of Gregor’s work. While there were many changes in matters of detail, explained in the introduction and notes to the bilingual edition, the principles of her approach – combining a high degree of faithfulness to Kant’s German with readability and fluency – naturally remained intact.

The Groundwork was first published in 1785. The translation follows the German text of the German–English volume, which is based on the second original edition of 1786. All major departures of the second original edition from the first are documented in the footnotes of this volume.

The concept of freedom is the key to the explanation of the autonomy of the will

A will is a kind of causality of living beings in so far as they are rational, and freedom would be that property of such a causality, as it can be efficient independently of alien causes determining it; just as natural necessity is the property of the causality of all non-rational beings to be determined to activity by the influence of alien causes.

The explication of freedom stated above is negative and therefore unfruitful for gaining insight into its essence; but there flows from it a positive concept of freedom, which is so much the richer and more fruitful. Since the concept of causality carries with it that of laws according to which, by something that we call a cause, something else, namely the consequence, must be posited: freedom, though it is not a property of the will according to natural laws, is not lawless because of that at all, but must rather be a causality according to immutable laws, but of a special kind; for otherwise a free will would be an absurdity. Natural necessity was a heteronomy of efficient causes; for every effect was possible only according to the law that something else determines the efficient cause to causality; what else, then, can 4:447 freedom of the will be, but autonomy, i.e. the property of the will of being a law to itself? But the proposition: the will is in all actions a law to itself, designates only the principle of acting on no maxim other than that which can also have itself as its object as a universal law. But this is just the formula of the categorical imperative and the principle of morality: thus a free will and a will under moral laws are one and the same.

It is impossible to think of anything at all in the world, or indeed even beyond it, that could be taken to be good without limitation, except a good will. Understanding, wit, judgment, and whatever else the talents of the mind may be called, or confidence, resolve, and persistency of intent, as qualities of temperament, are no doubt in many respects good and desirable; but they can also be extremely evil and harmful if the will that is to make use of these gifts of nature, and whose distinctive constitution is therefore called character, is not good. It is just the same with gifts of fortune. Power, riches, honor, even health, and the entire well-being and contentment with one’s condition, under the name of happiness, inspire confidence and thereby quite often overconfidence as well, unless a good will is present to correct and make generally purposive their influence on the mind, and with it also the whole principle for acting; not to mention that a rational impartial spectator can nevermore take any delight in the sight of the uninterrupted prosperity of a being adorned with no feature of a pure and good will, and that a good will thus appears to constitute the indispensable condition even of the worthiness to be happy.

Some qualities are even conducive to this good will itself and can make its work much easier; but regardless of this they have no 4:394 inner unconditional worth, but always presuppose a good will, which limits the high esteem in which they are otherwise rightly held, and makes it impermissible to take them for good per se. Moderation in affects and passions, self-control and sober deliberation are not only good in many respects, they even appear to constitute part of the inner worth of a person; but they are far from deserving to be declared good without limitation (however unconditionally they were praised by the ancients). For without principles of a good will they can become most evil, and the cold blood of a scoundrel makes him not only far more dangerous, but also immediately more loathsome in our eyes than he would have been taken to be without it.

Many philosophers believe there is a principle of practical reason that directs the rational agent to maximize the satisfaction of his own desires and interests. I will call this “the egoistic principle,” and the person who believes in it an “egoist.” Some philosophers believe that conformity to the egoistic principle is equivalent to the pursuit of happiness, or – if these are different – to the pursuit of the individual's own good. In the social sciences, especially economics, it is widely believed that some form of the egoistic principle is both normative and descriptive: that is, that it tells us not only how we should act, but also how, at least in clear-headed moments, we do act. Philosophers who endorse this view sometimes take the egoistic principle to be definitive of practical rationality, and therefore suppose that the way to show that we have “reason to be moral” is to show that conformity to moral requirements will somehow maximize the satisfaction of our own desires and interests.

This is not, of course, how the rationality of morality has been understood in either the Kantian or the rationalist tradition. Both Kant and Sidgwick, for instance, claimed that the moral principle is a principle of reason in its own right. But they also accepted the idea that something like the egoistic principle is a normative rational principle. For Sidgwick, the egoistic principle is a rival to the moral principle of utility.