Despite his love of hosting, conversation, and fine dining, Kant’s house was unadorned and austere. He had only one picture, which hung above his bureau. This picture was of Jean-Jacques Rousseau, who was only 12 years older than him. According to lore, the only time Kant failed to take his daily walk was when he received his copy of Rousseau’s Émile.

How did Rousseau’s outlook work its way into Kant’s moral philosophy? If for Rousseau, it is by following the “general will” that we can be said to be free, for Kant, it is by obeying those moral laws that we would will as universal laws. Moral laws that we would will as universal laws are given not by our individual will but by our rational will, which we have in common with all other rational beings.

We often experience this dichotomy in our minds: this is what I selfishly or frivolously want to do, and this is what I truly ought to do—because I want to live in a better society that abides by this rule, and would resent it if other people behaved in such a biased, thoughtless way.

To conform to the universal law is not to be a slave; on the contrary, it is to follow reason and free ourselves from our irrational and disordered appetites. For Kant, this capacity to overrule our individual will lies at the heart of our special dignity as human beings.

The Categorícal Imperative vs. the Golden Rule

When obeying those moral laws that we could consistently and rationally will as universal laws, we are following the so-called Categorical Imperative, which might be re-stated as, “Always act such that the maxim of your action can at the same time be upheld as a universal law.”

This is similar to the much older Golden Rule of the Bible, according to which we should treat others as we would want to be treated. But whereas the Golden Rule is based on personal desire, which is subjective (I might, for example, be a masochist, or be willing to tolerate a degree of mistreatment), the Categorical Imperative is based on reason, which is objective.

Hypothetical imperatives and consequentialism

Hypothetical imperatives are practical rules for achieving a desired outcome, for example, “If you want to lose weight, you should watch what you eat.” If you do not desire a particular outcome, you do not need to follow the rules. In this much, hypothetical imperatives are conditional and contingent. Categorical Imperatives, in contrast, are universal moral commands that bind everyone regardless of their aims, for example, “Do not lie” or “Do not steal.”

Hypothetical imperatives answer to the lower faculty of desire, which aims at pleasure. Categorical Imperatives answer to the higher faculty of will, which functions rationally and autonomously by following the laws which it legislates for itself, regardless of consequences or personal feelings.

For Kant, true moral actions must be motivated by duty, not some desired outcome. Thus, Kantian ethics are sometimes described as deontological, or duty-based, and contrasted with consequentialism (for example, utilitarianism), which is outcome-based. For Kant, moral systems based on outcomes or desires, such as utilitarianism, operate on hypothetical imperatives, not true moral law.

Perfect vs. imperfect duties

Kant provides some examples to add flesh to the bones of the Categorical Imperative. Imagine a person in financial need who borrows money and promises to pay it back, in the knowledge that they never will. If this action were universalised, promises of repayment would no longer be believed and the entire practice of lending would collapse. Kant also points out that abusing the lender in this way reduces a dignified being with ends of his own to a mere means to an end (“Act always treating humanity, in yourself and others, as an end and never merely as a means” is the second formulation of the Categorícal Imperative).

Second, imagine a person who does not intervene to help a person in distress. Were this maxim to be universalised, no one would ever help anyone, making the world into a worse place.

In the first case, not repaying a loan, the maxim cannot be universalised because it would involve a contradiction. In the second case, not helping a person in distress, there is no such contradiction. Nonetheless, it would not be rational to will a world in which no one ever helped anyone. Whereas repaying a loan is a “perfect duty,” helping someone in need is an “imperfect duty” in that we have some latitude in how we go about fulfilling it. Though we ought to be benevolent, we do not need to go about helping everyone all the time.

Failing in an imperfect duty, such as helping others or cultivating our talents, does not attract the same strict blame as violating a perfect duty, so long as we do not adopt a maxim contrary to the imperfect duty.

Kant’s example of the prudent grocer

When we do help someone, our action must be motivated by duty if it is to have moral worth. If I help someone from inclination, for example, from sympathy or because it makes me feel good, I am still doing a praiseworthy thing, but my action, being circumstantial rather than principled and reliable, lacks moral worth.

Imagine a grocer who always gives the correct change, but only to avoid being caught and losing his reputation. His behaviour, though not blameworthy, is lacking in moral worth. If he knew that he could not get caught, he may behave differently and dishonestly. Because his behaviour is prudential and circumstantial, rather than born out of duty, it is not categorical.

For Kant, a paradigm of moral worth is the person who hates life and longs to commit suicide, but stays alive purely out of duty. Because this person has no self-serving inclinations, he is acting purely from duty, rather than mere “conformity to duty.” Similarly, a hard-hearted person who has no other motivation than duty has a moral worth “beyond all comparison the highest.”

How to identify the Categorical Imperative

During his trial in Jerusalem in the 1960s, the Nazi Adolf Eichmann, a major organiser of the Holocaust, claimed to have been abiding by Kant’s Categorical Imperative—having interpreted “doing your duty” as blind obedience to superior authorities.

To identify the Categorical Imperative, we need to look inward to our rational self and engage in our own moral reasoning—asking whether the maxim guiding our action could be universalised—rather than delegate responsibility to some external authority such as a dictator (say, Hitler) or even a religious doctrine (say, the Ten Commandments).

So long as they reason correctly, every rational being, human or otherwise, should be able to arrive at the same Categorical Imperative. As pure rational wills, shorn of our attributes, temperaments, and desires, we are all the same. Whenever we carry out an action with a moral dimension, we implicitly universalise that action for all other wills.

In her analysis of the Eichmann trial, the philosopher Hannah Arendt introduced the concept of the “banality of evil,” highlighting that evil can be perpetrated not only by fanatics and psychopaths, but, more ordinarily, by “normal” people who fail to engage in critical self-reflection.