Immanuel Kant’s Groundwork of the Metaphysics of Morals was his first book in ethics. As indicated in the above quotation from the Preface (Kant 1997, 5/4:391), in this little book he attempted merely to “search for” and “establish” the supreme principle of morality. He did not intend here to pursue any other “moral investigation,” such as the development of a theory of rights, or of virtue. These he would bring out a dozen year later, in his final book in ethics, The Metaphysics of Morals (Kant 1991).

Structure of the text. The Groundwork is divided into three sections:

I. Transition from common rational cognition to philosophic moral cognition

II. Transition from popular moral philosophy to metaphysics of morals

III. Transition from metaphysics of morals to the critique of pure practical reason

The book is about the metaphysical foundations of morality. This implies that ethics is not based upon experience, but on a priori, metaphysical knowledge.

Critique of pure practical reason. A priori knowledge of the foundations of ethics, in line with Kant’s philosophical method, requires what he called a “critique.” Hence the title of the final section: “Transition from metaphysics of morals to the critique of pure practical reason.” Kant viewed a critique of this kind as a “purification” of reason. It is meant both to separate principles of reason from knowledge grounded in experience (a posteriori knowledge), and to limit reason, to ensure that it does not overstep its boundaries in a priori knowledge (see Kant 1998, Axxi). This is very abstract, and not likely to be understood by anyone unfamiliar with Kant’s wider, theoretical philosophy laid out in his Critique of Pure Reason.

Moral empiricism and Moral intuitionism. In the practical philosophy of ethics, the point of critique is to set aside both moral empiricism and what we now know as moral intuitionism. The knowledge of morality expected to result from this critique will not be derived from experience, nor from the supposed deliverances of rational intuition. It will be grounded instead in the presuppositions of our common practical life. For instance, the principles of morality confront us human beings with duties that, though we can fulfill, we do not necessarily fulfill. But if we were perfectly rational beings, or in Kant’s term, holy, we would not experience moral principles as constraints. The principles of morality would simply describe how we act. We would observe them like natural causes observing the laws of nature. Moral empiricism cannot account for what will be explained in the second section of the Groundwork as the “categorical” ought of moral duty. Experience can tell us what human beings do, or what they don't do, but it can never tell us what anyone ought to do. Rational intuitionism, on the other hand, cannot explain the human character of morality. What could be known through a pure, rational intuition of moral goodness or duty except the ideal of holiness unlimited by the shortcomings of human nature? We would know that a perfectly moral being would never lie, and never steal, and would keep all of his promises, and so on. But since we are not perfect, what should make us think that morality even applies to us? So what if rational intuition tells us how a perfect moral agent would act; what does that have to do with us? Why should we care? Rational intuition can tell us what a perfect circle would be—but it’s not like any of us can ever draw one, no matter how hard we try. So Kant’s philosophy of critique in ethics is meant to avoid what he sometimes called the “skepticism” of empiricism and the “dogmatism” of intuitionism.

Analytic and synthetic methods. The two aims of the Groundwork mentioned earlier require two philosophical methods: analysis and synthesis. The first aim, of searching for the supreme principle, requires analysis. Kant will analyze the knowledge of morality he thinks we already have, in order to make explicit the principle by which we determine the rightness and wrongness of actions. The second aim, of establishing the principle, requires synthesis. Here he will attempt to explain how we can know that the principle exists, as he says, or know that it applies to us. The first two sections of the Groundwork are devoted to the analytic project. The third section is devoted to the synthetic project.

Good will and the principle of duty. Here is a simple example of the analytic method. The idea of a “good will” refers, roughly, to doing the right thing simply because it is the right thing to do. Acting simply for the sake of doing the right thing is not acting for any ulterior motive—it is not acting in order to bring about something further, by doing what is right; something like someone’s trust, or a good reputation. So assuming that someone acts with a good will, this tell us that what the right thing to do is cannot be to bring about some new object or condition. For if it were, she would not have “doing the right thing” as her motive. She would instead act from her desire for the object she hopes to bring about—her good reputation, or some other satisfactory result. That is the first step of the analysis that begins in Section I of the Groundwork. The concept of acting with a good will is analyzed in order to show what could not be on the mind of someone acting with good will. But this presents only a negative result. It tells us how knowledge of what is the right thing to do is not determined. It is not determined based on some desirable object. Wanting to do something because it is right is one thing, wanting to bring about some object or advantage is another. As the analytic argument of the Groundwork continues in sections I and II, Kant will derive several, positive formulations of the principle of duty, which tell us how we can determine whether our actions is right or wrong.

Freedom and the intelligible world. The synthetic argument of the Groundwork, called the deduction, is deep and complicated. A key idea is freedom of the will. Kant will not prove in the Groundwork that we have this freedom. Several years earlier, in his Critique of Pure Reason, he had proved that it is possible that we are metaphysically free even if every event in experience must have a prior cause (Kant 1998, A538-58/B566-86). In the Groundwork he will claim only that there are good reasons for assuming that we belong to an “intelligible world,” where we act freely. That assumption, in turn, will imply that in acting in this “sensible” world we are “bound” by the law of that other world. The law of that world can only be the law Kant helps us see by analysis in the first two sections of the Groundwork: the principle of duty expressed by what he calls the “categorical imperative.”

Overview of ethics. Some popular approaches to ethics can be identified briefly to help situate Kant’s contribution to the field.

Consequentialism is the idea, roughly, that actions, policies and character can be assessed for their morality based on their effects. Versions of consequentialism differ mainly according to what they expect good or right actions to produce. They differ also in what they see as the object of moral assessment: the actions’ actual consequences, or the consequences agents aim to produce, regardless of their actual effects. Classical Utilitarianism, developed in the 18th and 19th centuries by Bentham and Mill, is the most well know example of consequentialism.

Deontology is the approach to ethics usually associated with Kant, although some recent interpreters have disputed this claim. Deontology assesses actions and traits of character based on their conformity to “duty.” An approach to ethics like this begins by explaining what duties there are, and how we know what they are. Sometimes Kantian ethics is thought to be the only deontological approach; but that is surely not correct. W.D. Ross, in the early 20th century, was a deontological intuitionist, and a critic of the Kantian view. The Ten Commandments presents a deontological ethics, since most of those commandments tell us how we ought to act, regardless of the consequences. The same seems to be true of the Hindu ethics of the Bhagavad Gita. It contains a famous scene where the god Krishna appears to the hero Arjuna on the field of battle, telling him why he ought to do his duty and slay his enemies, even if some of them are his kin.

Virtue Ethics is an ancient theory-type that has recently experienced a revival of interest. Here the primary object of moral assessment is character; and virtue ethics typically downplays the action-guiding principles emphasized in deontology, such as Kant’s supreme principle of duty. The virtuous person acts from good character, and needs no principles of action expressed in universal formulas. Both consequentialist and deontological ethics can include the assessment of character, but neither makes character primary, in the way that virtue ethics does.

Contractualism, yet another approach to ethics, is similar to deontology; but it allows consideration of consequences in ways that deontology seems not to allow. The most persuasive versions of contractualism emphasize a kind of ideal situation where parties to the moral contract are assumed to agree among themselves on what their rights and duties will be. The consequences of everyone’s having one set of duties or another are compared, and a set of principles is chosen by all, in light of their individual interests. Kant’s theory has some affinity with contractualism, as emphasized in the late 20th century by John Rawls, in his influential A Theory of Justice. In the Groundwork Kant writes briefly about the idea of a “kingdom of ends” that, as he describes it, seems comparable to a society whose members agree to abide by a common set of laws, as moral principles.

Criticism. Kant’s Groundwork of the Metaphysics of Morals has been in print, and translated, for well over 200 years. Because it is a seemingly simple book laying out the foundations of an attractive approach to ethics, it has been required reading for generations of philosophy students. Few students have readily understood its terminology, however. It has also been criticized for just about every argument it contains—but that’s what philosophers do. Most of the time, criticisms of the Groundwork’s arguments are based on pretty clear misinterpretations. But some criticisms are quite penetrating, and seem to be grounded in extremely plausible readings of what Kant wrote. Good interpretive work should be able to brush aside the former kind of criticism, take seriously the criticisms of the latter type, and respond to them with clearsighted honesty. That’s what I hope to do in the series of pages that follow.