44 Kantian Ethics (Main Concepts)

Although all of Kant’s work develops his ethical theory, it is most clearly defined in Groundwork of the Metaphysic of Morals, Critique of Practical Reason and Metaphysics of Morals. As part of the Enlightenment tradition, Kant based his ethical theory on the belief that reason should be used to determine how people ought to act.[1] He did not attempt to prescribe specific action, but instructed that reason should be used to determine how to behave.[2]

Good will and duty[edit]

In his combined works, Kant constructed the basis for an ethical law from the concept of duty.[3] Kant began his ethical theory by arguing that the only virtue that can be unqualifiedly good is a good will. No other virtue has this status because every other virtue can be used to achieve immoral ends (the virtue of loyalty is not good if one is loyal to an evil person, for example). The good will is unique in that it is always good and maintains its moral value even when it fails to achieve its moral intentions.[4] Kant regarded the good will as a single moral principle which freely chooses to use the other virtues for moral ends.[5]

For Kant a good will is a broader conception than a will which acts from duty. A will which acts from duty is distinguishable as a will which overcomes hindrances in order to keep the moral law. A dutiful will is thus a special case of a good will which becomes visible in adverse conditions. Kant argues that only acts performed with regard to duty have moral worth. This is not to say that acts performed merely in accordance with duty are worthless (these still deserve approval and encouragement), but that special esteem is given to acts which are performed out of duty.[6]

Kant’s conception of duty does not entail that people perform their duties grudgingly. Although duty often constrains people and prompts them to act against their inclinations, it still comes from an agent’s volition: they desire to keep the moral law. Thus, when an agent performs an action from duty it is because the rational incentives matter to them more than their opposing inclinations. Kant wished to move beyond the conception morality as externally imposed duties and present an ethics of autonomy, when rational agents freely recognise the claims reason makes upon them.[7]

Perfect and imperfect duties[edit]

Applying the categorical imperative, duties arise because failure to fulfil them would either result in a contradiction in conception or in a contradiction in the will. The former are classified as perfect duties, the latter as imperfect. A perfect duty always holds true—there is a perfect duty to tell the truth, so we must never lie. An imperfect duty allows flexibility—beneficence is an imperfect duty because we are not obliged to be completely beneficent at all times, but may choose the times and places in which we are.[8] Kant believed that perfect duties are more important than imperfect duties: if a conflict between duties arises, the perfect duty must be followed.[9]

Categorical Imperative[edit]

Main Article: Categorical Imperative

The primary formulation of Kant’s ethics is the categorical imperative,[10] from which he derived four further formulations.[11] Kant made a distinction between categorical and hypothetical imperatives. A hypothetical imperative is one we must obey if we want to satisfy our desires: ‘go to the doctor’ is a hypothetical imperative because we are only obliged to obey it if we want to get well. A categorical imperative binds us regardless of our desires: everyone has a duty to not lie, regardless of circumstances and even if it is in our interest to do so. These imperatives are morally binding because they are based on reason, rather than contingent facts about an agent.[12] Unlike hypothetical imperatives, which bind us insofar as we are part of a group or society which we owe duties to, we cannot opt out of the categorical imperative because we cannot opt out of being rational agents. We owe a duty to rationality by virtue of being rational agents; therefore, rational moral principles apply to all rational agents at all times.[13]


Kant’s first formulation of the Categorical Imperative is that of universalizability:[14]

Act only according to that maxim by which you can at the same time will that it should become a universal law.

— Immanuel Kant, Groundwork of the Metaphysics of Morals (1785)[15]

When someone acts, it is according to a rule, or maxim. For Kant, an act is only permissible if one is willing for the maxim that allows the action to be a universal law by which everyone acts.[15] Maxims fail this test if they produce either a contradiction in conception or a contradiction in the will when universalized. A contradiction in conception happens when, if a maxim were to be universalized, it ceases to make sense because the “…maxim would necessarily destroy itself as soon as it was made a universal law.”[16] For example, if the maxim ‘It is permissible to break promises’ was universalized, no one would trust any promises made, so the idea of a promise would become meaningless; the maxim would be self-contradictory because, when universalized, promises cease to be meaningful. The maxim is not moral because it is logically impossible to universalize—we could not conceive of a world where this maxim was universalized.[17]A maxim can also be immoral if it creates a contradiction in the will when universalized. This does not mean a logical contradiction, but that universalizing the maxim leads to a state of affairs that no rational being would desire. For example, Driver argues that the maxim ‘I will not give to charity’ produces a contradiction in the will when universalized because a world where no one gives to charity would be undesirable for the person who acts by that maxim.[18]

Kant believed that morality is the objective law of reason: just as objective physical laws necessitate physical actions (apples fall down because of gravity, for example), objective rational laws necessitate rational actions. He thus believed that a perfectly rational being must also be perfectly moral because a perfectly rational being subjectively finds it necessary to do what is rationally necessary. Because humans are not perfectly rational (they partly act by instinct), Kant believed that humans must conform their subjective will with objective rational laws, which he called conformity obligation.[19] Kant argued that the objective law of reason is a priori, existing externally from rational being. Just as physical laws exist prior to physical beings, rational laws (morality) exist prior to rational beings. Therefore, according to Kant, rational morality is universal and cannot change depending on circumstance.[20]

Humanity as an end in itself[edit]

Kant’s second formulation of the Categorical Imperative is to treat humanity as an end in itself:

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.

— Immanuel Kant, Groundwork of the Metaphysics of Morals (1785)[21]

Kant argued that rational beings can never be treated merely as means to ends; they must always also be treated as ends themselves, requiring that their own reasoned motives must be equally respected. This derives from Kant’s claim that reason motivates morality: it demands that we respect reason as a motive in all beings, including other people. A rational being cannot rationally consent to being used merely as a means to an end, so they must always be treated as an end.[22] Kant justified this by arguing that moral obligation is a rational necessity: that which is rationally willed is morally right. Because all rational agents rationally will themselves to be an end and never merely a means, it is morally obligatory that they are treated as such.[23][24][25] This does not mean that we can never treat a human as a means to an end, but that when we do, we also treat him as an end in himself.[22]

Formula of autonomy[edit]

Kant’s Formula of Autonomy expresses the idea that an agent is obliged to follow the Categorical Imperative because of their rational will, rather than any outside influence. Kant believed that any moral law motivated by the desire to fulfill some other interest would deny the Categorical Imperative, leading him to argue that the moral law must only arise from a rational will.[26] This principle requires people to recognize the right of others to act autonomously and means that, as moral laws must be universalisable, what is required of one person is required of all.[27][28][29]

Kingdom of Ends[edit]

Main article: Kingdom of Ends

Another formulation of Kant’s Categorical Imperative is the Kingdom of Ends:

A rational being must always regard himself as giving laws either as member or as sovereign in a kingdom of ends which is rendered possible by the freedom of will.

— Immanuel Kant, Groundwork of the Metaphysics of Morals (1785)[30]

This formulation requires that actions be considered as if their maxim is to provide a law for a hypothetical Kingdom of Ends. Accordingly, people have an obligation to act upon principles that a community of rational agents would accept as laws.[31] In such a community, each individual would only accept maxims that can govern every member of the community without treating any member merely as a means to an end.[32] Although the Kingdom of Ends is an ideal—the actions of other people and events of nature ensure that actions with good intentions sometimes result in harm—we are still required to act categorically, as legislators of this ideal kingdom.[33]


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