NOTE: This section discusses Kant’s Grounding for the Metaphysic of Morals and his Critique of Practical Reason, which are the subjects of much more detailed separate study guide treatments on SparkNotes.


Grounding for the Metaphysic of Morals, published in 1785, is Kant’s first major work in ethics. Like the Prolegomena to Any Future Metaphysics, Grounding for the Metaphysic of Morals is the short and easy-to-read version of what Kant deals with at greater length and complexity in his Critique. The Critique of Practical Reason, published three years later, contains greater detail than the Grounding for the Metaphysic of Morals and differs from it on some points—in the Critique of Practical Reason, for instance, Kant places greater emphasis on ends and not just on motives—but this summary and analysis will cover only the general points of Kant’s ethics, which both his major works share in common.

Morality applies to all rational beings, and a moral action is defined as one that is determined by reason, not by our sensual impulses. Because an action is moral on account of its being reasoned, the moral worth of an action is determined by its motive, or the reason behind the action, not by its consequences. We can determine the worth of the motive behind any given moral action by asking whether we could turn that motive into a universally applicable maxim. Reason is the same at all times and for all people, so morality too should be universal. Therefore, an action is moral only if it embodies a maxim that we could will to be a universal law.

Kant calls it a “categorical imperative” that we must act in such a way that we could will the maxim according to which we act to be a universal law. He contrasts this with the “hypothetical imperative,” which would demand that we act to achieve certain ends. The maxim of a hypothetical imperative would assert, “do such-and-such if you want to achieve such-and-such result.” There are no ifs in moral action, according to Kant. Morality works according to a categorical imperative because we must act in a given way simply because the motive is admirable, not because we have calculated that we can achieve certain ends as a result.

Once we recognize the universality of moral law, we must also recognize that it applies equally to all people. Acting morally, then, requires that we recognize other people as moral agents and always treat them as ends in themselves, not as means by which we can achieve our own ends. We must also ensure that our actions do not prevent other people from acting in accordance with moral law. Kant envisions an ideal society as a “kingdom of ends,” in which people are at once both the authors and the subjects of the laws they obey.

Morality is based in the concept of freedom, or autonomy. Someone with a free, or autonomous, will does not simply act but is able to reflect and decide whether to act in a given way. This act of deliberation distinguishes an autonomous will from a heteronomous will. In deliberating, we act according to a law we ourselves dictate, not according to the dictates of passion or impulse. We can claim to have an autonomous will even if we act always according to universal moral laws or maxims because we submit to these laws upon rational reflection.

Kant answers the tricky question of free will and determinism—how can we at once assert that we have a free will and that we live in a world that functions according to necessary physical laws?—by drawing on his distinction from the Critique of Pure Reason between the phenomenal world of appearances and the noumenal world of things-in-themselves. Physical laws apply only to appearances, whereas the will is a thing-in-itself about which we have no direct knowledge. Whether the will is actually free we can never know, but we still act in accordance with the idea of freedom.


In Kantian ethics, reason is not only the source of morality, it is also the measure of the moral worth of an action. Like some of his predecessors, Kant recognizes that our status as moral beings follows from our status as rational beings. That is, our actions can be considered moral or immoral to the extent that they are reasoned. However, in saying that rational decisions are open to moral judgment, we have not determined the grounds on which we should judge them. Many of the ethical theorists who preceded Kant attempt to ground moral judgment in the law of God or of a sovereign monarch. Kant recognizes that grounding morality in an externally imposed law compromises the autonomy of the will: in such a case, we act under a feeling of compulsion to a will that is not our own, and so we are not entirely accountable for our actions. We act autonomously only if we act in accordance with a law dictated by our own reason. While earlier philosophers recognize that rationality is the source of morality, Kant is the first to argue that reason also provides the standard by which we make moral evaluations.

Kant’s ethics is the most influential expression of an approach to ethics known as deontology, which is often contrasted with consequentialism. The distinctive feature of deontology is that it approves or disapproves of actions in and of themselves. For instance, according to Kant, lying is always wrong because we cannot will it as a universal maxim that lying is okay. The consequentialist view, by contrast, argues that moral value lies not in our actions but in their consequences.

The utilitarianism of John Stuart Mill is one of the most influential forms of consequentialist ethics. Mill argues that we should always aim at ensuring the greatest happiness for the greatest number of people and that, for instance, telling a lie in particular consequences is good if telling that lie produces good consequences. The consequentialist view has the intuitive appeal that we presumably determine that actions are good or not depending on the effect they actually have. However, a Kantian would argue against this view, pointing out that we have full control only over our motives, not the consequences of our actions, so our autonomous will can only approve or disapprove of motives. An ethics that focuses on consequences, then, is not based in the autonomy of the will.

Kantian ethics rely on a universalist conception of reason and morality that is characteristic of the Enlightenment. Kant is quite clear that his ethics apply equally to all people. We can only consider an action moral if we could will that it apply as a universal law to everyone, and we should aspire to a “kingdom of ends,” in which everyone is both author and subject to the moral laws dictated by reason. This conception of morality was first questioned by Hegel, who argued that morality varies depending on cultural and historical circumstances, and moral relativism has become a foundation stone of the postmodern worldview.

A postmodernist critique of Kant would suggest that Kant is insufficiently sensitive to the great variety of individual experience and that it is paternalistic, if not arrogant, to assume that one can apply one’s own moral standards to peoples and cultures of which one has no understanding. A Kantian would reply that Kantian ethics are based in a shared humanity that applies to all people. Certainly, we adopt different practical identities, such that we might hold different values depending on whether we identify, say, as a Canadian, a postal worker, or a jazz aficionado. However, Kantian ethics are based not on these particular practical identities but on our shared identity as rational beings, which we cannot revoke without revoking our humanity.

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