Immanuel Kant
(1724-1804)

Immanuel Kant was born in the East Prussian city of Königsberg, studied at its university, and worked there as a tutor and professor for more than forty years, never travelling more than fifty miles from home. Although his outward life was one of legendary calm and regularity, Kant’s intellectual work easily justified his own claim to have effected a Copernican revolution in philosophy. Beginning with his Inaugural Dissertation (1770) on the difference between right- and left-handed spatial orientations, Kant patiently worked out the most comprehensive and influential philosophical programme of the modern era. His central thesis—that the possibility of human knowledge presupposes the active participation of the human mind—is deceptively simple, but the details of its application are notoriously complex.

Towards the end of his most influential work, Critique of Pure Reason (1781/1787), Kant argues that all philosophy ultimately aims at answering these three questions: “What can I know? What should I do? What may I hope?” The book appeared at the beginning of the most productive period of his career, and by the end of his life Kant had worked out systematic, revolutionary, and often profound answers to these questions.

At the foundation of Kant’s system is the doctrine of “transcendental idealism,” which emphasizes a distinction between what we can experience (the natural, observable world) and what we cannot (“supersensible” objects such as God and the soul). Kant argued that we can only have knowledge of things we can experience. Accordingly, in answer to the question, “What can I know?” Kant replies that we can know the natural, observable world, but we cannot, however, have answers to many of the deepest questions of metaphysics.

The monumental Kritik der reinen Vernunft (Critique of Pure Reason) (1781, 1787) fully spells out the conditions for mathematical, scientific, and metaphysical knowledge in its “Transcendental Aesthetic,” “Transcendental Analytic,” and “Transcendental Dialectic,” but Kant found it helpful to offer a less technical exposition of the same themes in the Prolegomena zu einer jeden künftigen Metaphysik die als Wissenschaft wird auftreten können (Prolegomena to any Future Metaphysic) (1783). Carefully distinguishing judgments as analytic or synthetic and as a priori or a posteriori, Kant held that the most interesting and useful varieties of human knowledge rely upon synthetic a priori judgments, which are, in turn, possible only when the mind determines the conditions of its own experience. Thus, it is we who impose the forms of space and time upon all possible sensation in mathematics, and it is we who render all experience coherent as scientific knowledge governed by traditional notions of substance and causality by applying the pure concepts of the understanding to all possible experience. But regulative principles of this sort hold only for the world as we know it, and since metaphysical propositions seek a truth beyond all experience, they cannot be established within the bounds of reason.

Significant applications of these principles are expressed in Metaphysische Anfangsgründe der Naturwissenschaft (Metaphysical Foundations of the Science of Nature) (1786) and Beantwortung der Frage: Ist es eine Erfahrung, daß wir denken? (On Comprehension and Transcendental Consciousness) (1788-1791).

In later life, Kant drew art and science together under the concept of purpose in the Kritik der Urteilskraft (Critique of Judgment) (1790), considered the consequences of transcendental criticism for theology in Die Religion innerhalb die Grenzen der blossen Vernunft (Religion within the Limits of Reason Alone) (1793), stated the fundamental principles for civil discourse in Beantwortung der Frage: Was ist Aufklärung? (“What is Enlightenment?” (1784), and made an eloquent plea for international cooperation in Zum ewigen Frieden (Perpetual Peace) (1795).

Kant’s Moral Philosophy

We begin with the concept of that which can be conceived to be good without qualification, a good will. Other good features of human nature and the benefits of a good life, Kant pointed out, have value only under appropriate conditions, since they may be used either for good or for evil. But a good will is intrinsically good; its value is wholly self-contained and utterly independent of its external relations. Since our practical reason is better suited to the development and guidance of a good will than to the achievement of happiness, it follows that the value of a good will does not depend even on the results it manages to produce as the consequences of human action.

Kant’s moral theory is, therefore, deontological: actions are morally right in virtue of their motives, which must derive more from duty than from inclination. The clearest examples of morally right action are precisely those in which an individual agent’s determination to act in accordance with duty overcomes her evident self-interest and obvious desire to do otherwise. But in such a case, Kant argues, the moral value of the action can only reside in a formal principle or “maxim,” the general commitment to act in this way because it is one’s duty. So he concludes that “Duty is the necessity to act out of reverence for the law.”

According to Kant, then, the ultimate principle of morality must be a moral law conceived so abstractly that it is capable of guiding us to the right action in application to every possible set of circumstances. So the only relevant feature of the moral law is its generality, the fact that it has the formal property of universalizability, by virtue of which it can be applied at all times to every moral agent. From this chain of reasoning about our ordinary moral concepts, Kant derived as a preliminary statement of moral obligation the notion that right actions are those that practical reason would will as universal law.

Imperatives for Action

More accurate comprehension of morality, of course, requires the introduction of a more precise philosophical vocabulary. Although everything naturally acts in accordance with law, Kant supposed, only rational beings do so consciously, in obedience to the objective principles determined by practical reason. Of course, human agents also have subjective impulses—desires and inclinations that may contradict the dictates of reason. So we experience the claim of reason as an obligation, a command that we act in a particular way, or an imperative. Such imperatives may occur in either of two distinct forms, hypothetical or categorical.

A hypothetical imperative conditionally demands performance of an action for the sake of some other end or purpose; it has the form “Do A in order to achieve X.” The application of hypothetical imperatives to ethical decisions is mildly troublesome: in such cases it is clear that we are morally obliged to perform the action A only if we are sure both that X is a legitimate goal and that doing A will in fact produce this desirable result. For a perfectly rational being, all of this would be analytic, but given the general limitations of human knowledge, the joint conditions may rarely be satisfied.

A categorical imperative, on the other hand, unconditionally demands performance of an action for its own sake; it has the form “Do A.” An absolute moral demand of this sort gives rise to familiar difficulties: since it expresses moral obligation with the perfect necessity that would directly bind any will uncluttered by subjective inclinations, the categorical imperative must be known a priori; yet it cannot be an analytic judgment, since its content is not contained in the concept of a rational agent as such. The supreme principle of morality must be a synthetic a priori proposition. Leaving its justification for the third section of the Grounding (and the Second Critique), Kant proceeded to a discussion of the content and application of the categorical impetative.

The Categorical Imperative

Constrained only by the principle of universalizability, the practical reason of any rational being understands the categorical imperative to be: “Act only according to that maxim whereby you can at the same time will that it should become a universal law.” That is, each individual agent regards itself as determining, by its decision to act in a certain way, that everyone (including itself) will always act according to the same general rule in the future. This expression of the moral law, Kant maintained, provides a concrete, practical method for evaluating particular human actions of several distinct varieties.

Although he held that there is only one categorical imperative of morality, Kant found it helpful to express it in several ways. Some of the alternative statements can be regarded as minor variations on his major themes, but two differ from the “formula of universal law” sufficiently to warrant a brief independent discussion….

Kant offered the “formula of the end in itself” as: “Act in such a way that you treat humanity, whether in your own person or in the person of another, always at the same time as an end and never simply as a means.” This places more emphasis on the unique value of human life as deserving of our ultimate moral respect and thus proposes a more personal view of morality. Thus, one is morally prohibited from making a false promise (or killing oneself) because to do so would treat another person (or myself) merely as a means for getting money (or avoiding pain), which in turn means it cannot accord with the formula of universal law; this is an instance of a perfect duty, which must always be heeded. (An imperfect duty is one that should be heeded as often as possible, but is not always expected, depending on circumstance, goals, etc., such as giving to charity.) Thus, the Kantian imperative agrees with the Christian expression of “The Golden Rule” by demanding that we derive from our own self-interest a generalized concern for all human beings.

Drawing everything together, Kant arrived at the “formula of autonomy,” under which the decision to act according to a maxim is actually regarded as having made it a universal law. Here the concern with human dignity is combined with the principle of universalizability to produce a conception of the moral law as self-legislated by each for all. As Kant puts it,

A rational being belongs to the kingdom of ends as a member when he legislates in it universal laws while also being himself subject to these laws. He belongs to it as sovereign, when as legislator he is himself subject to the will of no other.

A rational being must always regard himself as legislator in a kingdom of ends rendered possible by freedom of the will, whether as member or as sovereign.

In this final formulation, the similarity of Kant’s moral theory with his epistemology should be clear. Just as the understanding in each of us determines the regulative principles of natural science that all must share, so the practical reason in each of us determines the universal maxims of morality that all must obey.

Autonomy of the Will

In fact, this final formula for the categorical imperative brings us back to the original concept of the will itself as that which is good without qualification. At this point in the argument, Kant can provide a more technical statement of its intrinsic moral value by distinguishing between autonomy and heteronomy of the will.

A heteronomous will is one in obedience to rules of action that have been legislated externally to it. Such a will is always submitting itself to some other end, and the principles of its action will invariably be hypothetical imperatives urging that it act in such a way as to receive pleasure, appease the moral sense, or seek personal perfection. In any case, the moral obligations it proposes cannot be regarded as completely binding upon any agent, since their maxim of action comes from outside it.

An autonomous will, on the other hand, is entirely self-legislating: The moral obligations by which it is perfectly bound are those which it has imposed upon itself while simultaneously regarding them as binding upon everyone else by virtue of their common possession of the same rational faculties. All genuinely moral action, Kant supposed, flows from the freely chosen dictates of an autonomous will. So even the possibility of morality presupposes that human agents have free will, and the final section of the Grounding is devoted to Kant’s effort to prove that they do.