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Categorical Imperative

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The philosophical concept of a categorical imperative is central to the moral philosophy of Immanuel Kant. In his philosophy, it denotes an absolute, unconditional requirement that allows no exceptions, and is both required and justified as an end in itself, not as a means to some other end; the opposite of a hypothetical imperative. Most famously, he holds that all categorical imperatives can be derived from a single one, which is known as "the" Categorical Imperative (capitalized); it is upon this Imperative that the article will focus.



In his Groundwork of the Metaphysic of Morals, Kant formulates the Categorical Imperative in three different ways:

  • The first (Universal Law formulation): "Act only according to that maxim by which you can at the same time will that it should become a universal law."
  • The second (Humanity or End in Itself formulation): "Act in such a way that you always treat humanity, whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end."
  • The third (Kingdom of Ends formulation) combines the two: "All maxims as proceeding from our own [hypothetical] making of law ought to harmonise with a possible kingdom of ends."


In Kant's view immorality occurs when the categorical imperative is not followed: when a person attempts to set a different standard for themselves than for the rest of humanity. In the Groundwork for the Metaphysics of Morals, once Kant has derived his categorical imperative he applies it to a number of examples. The second example and probably the most analysed is that of an unfaithful promise. Kant applies his imperative to a person who is short of money who intends to ask for a loan, promising to repay it, but with no intention of doing so. When Kant applies the categorical imperative to this situation he discovers that it leads to a contradiction, for if breaking promises were to become universal then no person would ever agree to a promise and promises would disappear. Kant connects rationality with morality, and sees contradictory behaviour as immoral. Some critics have argued that Kant never asserts the connection between rationality and morality, but most dismiss this and point out that Kant clearly explains how morality must be based upon reason and not upon desires.

Rejection of Aristotle

Especially important to Kant were the works of Aristotle, which stand in direct opposition to much of what Kant argues. Before Kant the most important moral theories were based upon Aristotle's Nicomachean Ethics which assert that whatever leads to greater eudaimonia, or happiness, is what is moral. Kant, however, believes that any action taken for a deliberate end, whether it be happiness or some other goal, is morally neutral. Kant rests his rejection of the Aristotelian position on a number of points. He points out that all the imperatives are hypothetical, they are performed merely to attain a certain end. More importantly to Kant, this end is one dictated by desires, implying that the human will is no more than a facilitator of predetermined ends, limiting human freedom.

Kant also challenges the traditional viewpoint using his definition of duty as something that is impossible to learn from observation, and thus can only be deduced rationally. While it is possible to learn imperatives of skill and prudence that are morally neutral through observation, the categorical imperative that allows one to determine what actually is moral is known a priori and can only be properly determined through reason. Any imperative that is hypothetical is not based on reason. You perform a hypothetical imperative only if you want or desire something; they are performed for a certain hoped for end. They are based on desire and hope and not upon the reason upon which ethics should be founded.

Equivalence of the formulas

One problem is how Kant can possibly regard the first two formulas as equivalent. The answer may lie in the fundamental motivation for the Categorical Imperative—it is essentially based on a conception of fairness and universalizability. I must realise that there must be a consistent law for everyone—there cannot be one rule for me and another for everyone else.

For example, stealing would fail the test, since, to steal, you must deny the existence of property rights. But in so doing, you would be denying ownership of your own property, and the whole act of stealing would become (in Kant's eyes) logically self-defeating.

This desire for consistency drives the first formulation - could I consistently will that stealing became a universal law? Of course not. The same goes for killing, lying, and so on - I cannot will that these be universally practiced, since if they were it would be harmful to me. Any such actions I carry out are thus inconsistent with reason. There are also more subtle effects: for example, I cannot decide never to help others out, as I must recognise that I am likely to need help from others at some point.

The second formulation can be seen as following from the first - if we are tempted to use other people merely as a means, we must realise that a universal law that allowed this would harm us. So the second formulation can be seen as just an example of a universal law willed under the first formulation.

More than this, however, the second formulation is again based on a concept of fairness - although I recognise the importance of myself as an end (that is, a person with hopes, desires, and so on), I must realise that what is special about me as a rational being also makes everyone else special, and they too must be seen as ends-in-themselves. So I must regard all persons as ends-in-themselves, rather than just as means to my ends, which are, after all, no more important than anyone else's.

Thus, the first two formulations (and therefore the third, which combines the two) can arguably be seen as closely tied together.


Since the publication of the Groundwork, many new opponents have arisen and they too have tried to challenge the effectiveness of the imperative.

The enquiring murderer

One of the first major challenges to Kant's reasoning came from the Swiss philosopher Benjamin Constant who asserted that since truth telling must be universal according to Kant's theories, one must (if asked) tell a known murderer the location of his prey.

This challenge occurred while Kant was still alive and his response was the now infamous essay On a Supposed Right to Tell Lies from Benevolent Motives. In this reply Kant argued that it is indeed one's moral duty to be truthful to a murderer, a statement which seems to contradict Kant's earlier assertions that his moral theory is the one that people practice subconsciously anyway. The scholar Paton, usually a great Kant fan, has called this letter a temporary aberration, and the petulant reply of a 73 year old man.

It is worth noting that the example can be restated in such a way that "no comment" will confirm to the murderer the location of the victim, and so the only way to save the victim is to lie. In any event, saying "no comment" probably violates the Categorical Imperative anyway, since one cannot will that everyone would always respond to questions in such a manner. Thus, arguably, the Categorical Imperative requires truthfulness, rather than just prohibiting lies.

Kant believed the world would be shocked by how vast the uses and implications of his categorical imperative would be. After Constant, however, the uses were either dramatically lessened, or it had to be accepted that the moral system Kant was proposing would stand in opposition to the intuitions of the average person.

Indeed the uses and implications of the categorical imperative are vast. It prescribes universal behavior, a thing which is beyond the capability of the average person to comprehend. Average concepts of morality are of no importance to it. When examining the morality of truth-telling, one must fully consider the expected consequences and the act of telling the truth. In the case of the murderer, telling the truth allows a person to be murdered, and thus the truth-teller has essentially sanctioned murder. Just as it is immoral to commit murder, it is immoral to abet murder: it cannot be willed that all people would make themselves accomplice to murder. It is not only permissible to lie in circumstances where all people must be expected to lie; it is required. Thus, the answer to this challenge resides in the proper formulation of the maxim of action, which includes not only the lying but also the abetting of murder.

Kant argued that the telling the truth to the murderer is required because the action itself is of value, regardless of the consequences. One does not know what will happen in the future. It might turn out that if you lied about where the victim is, you would be morally responsible for that lie. For example, say you said the victim was in the park, when you thought he was in the library. However, little did you know, the victim actually left the library and went to the park. The lie would actually lead the murderer to the victim. Another example post-Kantians bring up is that you would not be morally responsible for the action, the murderer would be. If you told the truth, it might turn out the murderer decides not to murder after all. However, many philosophers deny these objections as fanciful thinking, impractical for real world situations.

Universal oath-breaking

Another objection to Kant came from the Englishman Sir David Ross who pointed that a world where everyone could be depended upon to always break their promises would be just as effective and reliable as a world where everyone kept their promises and one could thus will that promise breaking become universal.

The reply to this is that a world where one could always rely on everyone to break their promises would be the same world as one with promises but with a different language. The word 'not' in a phrase such as "I promise not to go to class today" would no longer mean a negation of a promise but would be an essential part of a promising phrase. Because the language is different does not change the act of promising at all; promises would still exist and one would still expect them to be carried through.

Prudential vs. moral maxims

Another problem for Kant's moral theory was that it has difficulty proving what is a moral maxim, and what is merely a prudential maxim. Louis White Beck used the example of the maxim that the purchaser of every new book should write their name on the flyleaf. There is nothing in the categorical imperative to discern that this is not a moral imperative for it is easily something which one would wish to be universally applied, and this universal application would lead to no irrational contradictions. Of course this imperative is actually hypothetical, but the condition is merely omitted. One could say that you should always inscribe your name inside a new book, if you want it to be returned. The categorical imperative on its own cannot differentiate between a prudential maxim and one that is truly moral--this requires a longer and more complex method of reasoning.

The difference between what is moral and what is merely prudential cannot be understood except with reference to the second maxim. One can certainly act in any way one chooses on a local scale and consider oneself moral: but this involves only a local group of people, not the universal whole. True morality can only be found when one acts with mindfulness of the interests of all people.

False negatives

The categorical imperative sometimes seems to give false negatives in terms of what is permitted behaviour. For example, I cannot will that everyone in the world should eat at my favorite restaurant.

This sort of problem can be avoided by being careful in the use of relative terms like my. In this case, it is possible to will that everyone should eat at his or her favourite restaurant. Again, this is an issue of the proper formulation of the maxim of action. A properly formed maxim would avoid the particular or singular, as it is to be tested for its universality.

Suicidal thoughts

The critique of Ayn Rand amounts to this reductio ad absurdum: The deduction that the entire human race has a duty to die is entirely consistent with the Categorical Imperative provided that the deducer agrees that he himself, or she herself, has a duty to die too - regardless of any, some or all's inclination, rooted in self-love, to stay alive. At the root of her critique is her conclusion that Kantian appeals to the good implicitly appeal to Aristotle's eudaimonia while explicitly denying its relevance to morals. An example: a duty to promote universal war is exactly the same as a duty to promote universal peace once eudaimonia is removed.

Attempts to combine with Kantian ethics

James Cornman holds that one may overcome the shortcomings of both Kant's categorical imperative and the shortcomings of Utilitarianism by combining them. The basic rule is that in any situation we must (a) treat as mere means as few people as possible, and (b) treat as ends as many people as is consistent with (a).

"He suggests that a Kantian ethic does not have to be nonconsequentialist, and that a utilitarian ethic does not have to reject the notion of a categorical imperative - in other words, that it makes sense to propose Ďa utilitarian Kantian principleí. This will involve grafting the utilitarian principle onto Kantís second formulation." (The Quest for an Ultimate Standard 2: Kantian Ethics)

Cornman describes the Utilitarian Kantian Principle in this way:

An action ought to be done in a situation if and only if:
1. Doing the action:
(a) treats as mere means as few people as possible in the situation, and
(b) treats as ends as many people as is consistent with (a).
2. Doing the action in the situation brings about as much overall happiness as is consistent with (1).
(Cornman, p. 346-347, 1992)

Related topics


  • Cornman, James, et al. 1992 Philosophical Problems and Arguments - An Introduction, 4th edition Indianapolis: Hackett
  • Michael Martin, "A Utilitarian Kantian Principle," Philosophical Studies, (with H. Ruf), 21, 1970, pp. 90-91.
  • Silverstein, Harry S. A Defence of Cornmanís Utilitarian Kantian Principle, Philosophical Studies (Dordrecht u.a.) 23, 212-215. 1972

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