Immanuel Kant’s Groundwork of the Metaphysic of Morals (Grundlegung zur Metaphysik der Sitten, 1785) develops the logical foundation for a moral philosophy which is based on a priori rather than empirical principles. Kant proposes a rationalist theory of ethics, arguing that ethical judgments should be based on pure reason. Kant maintains that rationalism in making ethical judgments is necessary because only pure reason can define practical principles of morality which have universal validity.

The Groundwork of the Metaphysic of Morals includes a preface and three chapters. The preface of the Groundwork explains that its aim is to provide a rule of pure practical reason for moral philosophy and is thereby to establish a supreme principle of morality. The first chapter discusses the nature of moral duty and the importance of good will. The first chapter also explains the necessity of the 'categorical imperative.' The second chapter discusses the classification of imperatives, the formulation of a supreme principle of morality, and the properties belonging to the human will. The third chapter discusses the importance of freedom as a key to explaining the 'autonomy' of the will.

Kant argues that there are universal moral laws which are not merely empirical but which are logically necessary. An action which is good should not only conform to a moral law, but should be done for the sake of a moral law.¹ If an action conforms to a moral law, but is not done for the sake of a moral law, then its conformity is merely contingent to subjective conditions, and is not logically necessary. Kant emphasizes that moral philosophy cannot be merely an empirical inquiry, but that it must be a metaphysical inquiry, and that it must be based on pure practical reason.

Kant also argues that reason can influence the will, and that it can produce a will which is good. Good will is not merely a means of producing good moral conduct, but is an end in itself.² Good will can motivate an individual to obey his or her sense of moral duty. Furthermore, the moral value of an action is determined by whether the action is motivated by a sense of moral duty. Actions which conform with moral obligation or duty, but which are not motivated by a sense of duty, are lacking in the moral content which they would have if they were motivated by a sense of duty.

Kant argues that if an action is motivated by a sense of duty, then the moral value of the action is determined not by the purpose for which the action is performed, but by the principle according to which the action is decided upon. Thus, the moral value of an action is determined not by how effective the action is in achieving its object, but by the principle of volition according to which it is performed.³

According to Kant, the 'categorical imperative' is to act in such a way that the principle according to which the action is performed can be accepted as a universal law of morality. This can be stated as the command to "Act only in such a way that you can will that the maxim of your action should become a universal law."⁴ Kant defines a maxim as a subjective principle of volition, and he defines a law as an objective principle of reason. Thus, an action is good if it is produced by a unity of subjective and objective motivation, i.e. if the subjective principle of volition which motivates the action becomes an objective principle of reason.

Kant also argues that moral necessity is established by reason and not by experience, because experience can only establish that a moral principle is true or valid under certain conditions and not that a moral principle is necessarily true or valid under all conditions. The truths which are established by experience are therefore contingent truths and are not logically necessary truths.

Kant explains that if reason determines the will, then the actions which are chosen by the will are not only subjectively necessary, but are also objectively necessary. If the will is not determined by reason, then the actions which are chosen by the will may only be contingent to subjective conditions and may not be objectively necessary.

The 'categorical imperative,' according to Kant, is a command or duty to act according to an objective principle of reason. Since the will may not always be completely determined by reason, Kant explains that subjective principles of volition should conform to objective principles of reason. He also explains that the 'categorical imperative' is necessary only for an imperfect will. A perfect will aims to do everything that is necessary and has no need of any moral imperatives, because it seeks to do only what is good.

Kant argues that moral imperatives may be classified as either hypothetical or categorical. A 'hypothetical imperative' determines an action to be practically necessary for the attainment of some purpose or goal beyond itself. A 'categorical imperative' determines an action to be objectively necessary, regardless of any purposes or goals beyond the action itself. The purpose for which an action is affirmed to be good may be possible or actual. A 'hypothetical imperative' asserts that an action is good for some purpose or goal, but a 'categorical imperative' does not refer to the purpose or goal of an action and asserts that the action is good in itself.⁵

Kant explains that there is no 'categorical imperative' for an action which is judged to be good for promoting happiness, because there is no way to determine with certainty in every case what will make an individual truly happy. An action which is judged to be good for promoting happiness can only be determined to be necessary by a 'hypothetical imperative.'

Kant also explains that a 'categorical imperative' is a universal law of morality. A 'hypothetical imperative' is an objective principle, but is not a universal law. A 'hypothetical imperative' commands that an action be performed for some other purpose than the action itself. Thus, if the purpose of the action is abandoned, a 'hypothetical imperative' may determine that the action is no longer necessary. In contrast, a 'categorical imperative' determines an action to be necessary under all conditions, and is thus a universal law of the will.

Kant argues that there is only a single 'categorical imperative,' which is to 'act only in such a way that you can will that the maxim of your actions should become a universal law.'⁶ If there were more than one categorical imperative, then more than one universal law of morality would be necessary. However, if the 'categorical imperative' is to 'act only in such a way that you can will that the maxim of your action should become a universal law,' then the 'categorical imperative' is itself a universal law which applies to every action. Thus, only one 'categorical imperative' is necessary.

Kant asserts that the 'categorical imperative' is a practical law for the will of every human being. To the extent that each individual can determine his or her own will, each individual may be able to will that the maxim of his or her actions should become a universal law of morality. However, in order for the maxim of each of these actions to become a universal law of morality, the actions themselves must not be self-contradictory.

According to Kant, the moral value of an action may be determined by the extent to which the action conforms to the 'categorical imperative.' The moral value of an action may also be determined by whether the action more closely conforms to the 'categorical imperative' than some other action which could be performed.

Kant explains that the 'autonomy' of the will is the capacity of the will to be a law to itself, because the will is the agent through which the maxim of an action can become universal law. The freedom of the will is revealed by its 'autonomy.' The 'heteronomy' of the will is the capacity of the will to follow a law other than itself when it seeks a purpose in an object of subjective volition. Kant explains that the 'autonomy' of the will produces a universal law of morality, but that the 'heteronomy' of the will produces spurious principles of morality.

In the final chapter of the Groundwork, Kant discusses the relation between freedom and necessity. He argues that freedom of the will is compatible with natural necessity. Freedom and necessity are combined in any action which is performed according to practical reason. Freedom of the will is not the capacity of the will to make choices on the basis of subjective volition, but is the capacity to choose actions on the basis of objective principles of reason.

Kant makes a variety of assumptions in arguing that there is a supreme principle of morality. Some of these assumptions include: 1) that there are universal moral laws, 2) that there are principles of morality which exist independently of the situations in which moral decisions are made, 3) that logically necessary moral truths can be determined only by reason and not by experience, 4) that any moral philosophy which is logically valid must be based on pure reason, 5) that the motive of an action is more important than the consequences of the action, 6) that the moral value of an action should only be judged by the motives of the action and not by the consequences of the action, and 7) that in order to be good, an action must only be performed for the sake of a moral law and not for some other purpose. The validity of Kant’s theory of a universal law of morality may be related to whether these assumptions are accepted or rejected.

Kant defines moral duty as a practical necessity of action which arises from reverence or respect for a moral law. According to Kant, moral duty enables good will to determine which actions are morally necessary. Duty is a motive for the rational will, but is a source of conflict for the irrational will. Kant does not fully explore the nature of this conflict. Moreover, he does not discuss the coercive aspect of moral duty or the impact which coercion or constraint may have on moral freedom.

It may also be argued that Kant’s theory of universal moral laws tends to polarize moral judgments by reducing them to statements about what is lawful or unlawful. The concept of a 'categorical imperative' may oversimplify the moral complexity of situations in which there is moral ambiguity, and may not be applicable to situations in which some degree of moral compromise may be necessary. The theory of the 'categorical imperative' may not be adaptable to situations in which there is not a perfect choice of moral action.

¹Immanuel Kant, Groundwork of the Metaphysic of Morals, translated by H.J. Paton (New York: Harper & Row, 1964), p.58.
²Ibid., p. 64.
³Ibid., p. 68.
⁴Ibid., p. 70.
⁵Ibid., p. 82.
⁶Ibid., p. 88.
⁷Ibid., p. 108.

Kant, Immanuel. Groundwork of the Metaphysic of Morals. Translated by H.J. Paton. New York: Harper & Row, 1964.