After reading The Groundwork of the Metaphysics of Morals, I'm still unsure why human beings have a duty to obey the Categorical Imperative. I understand Kant's argument why a rational will necessarily obeys it, but I do not see how it carries the force of an "ought", and thus why beings not bound by perfect rationality (e.g. humans) ought follow it. My suspicion is that Kant requires a good will to be rational, and since he holds that only a good will has intrinsic moral value the conclusion that we have a duty to obey the CI follows. This seems to be supported by the Stanford Encyclopedia of Philosophy, which states:

In Kant's terms, a good will is a will whose decisions are wholly determined by moral demands or as he often refers to this, by the Moral Law.

This implies that a good will is rational, as according to Kant any moral demand must be completely rational. However, I haven't been able to find strong textual support for this in Groundwork.

Is my suspicion correct? If not, what makes the CI an "ought" rather than just something a perfectly rational will would do?

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    Why do you think Kant actually meant the CI as a "duty"? - It is an Imperative and as long as you stick to German grammar you are not bound to it. This is expressed by the German word "sollen", which I hope is fittingly translated with should: "You should not kill people."
    – Sim
    Commented May 7, 2012 at 21:02
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    "The imagination of an objective Principle, as long as needed for a good will, is called a commandment, the the formula of that commandment is called imperativ. All Imperatives are expressed with 'should', which shows the relation between objective law to a will which is, due to his structural quality, not controlled by it." - The Groundwork of the Metaphysics of Morals Page 56-57 Ger. Reclam (hope it didn't turn out too bad, but translating Kant from German to English is a pain)
    – Sim
    Commented May 7, 2012 at 21:08
  • Haven't read it, and I'm someone who is not much interested in this kind of philosophy. But for what it's worth, I think Kant is taking part in a kind of game, like someone feeling the thrill of being the greatest chess player, but it is only a game. He is not uncovering objective truths about the "real" world. And your question presupposes that there is something externally real there which might be discovered. I believe there are externally real things, which cause our sensations of "flower" and "rain" etc, and cause our beliefs that "Redrum was the winner of the 2.30 at Ascot", but the cate
    – user2137
    Commented Jul 20, 2012 at 9:46

4 Answers 4


Utilitarianism, virtue ethics and deontological ethics draw their justification from consistency with our cultural values and/or intuitions.

Kant's categorical imperative is the basis for one of very few moral theories that attempts to derive morality from purely logical means. (It is possibly the only complete theory to do so). It's power comes from its lack of dependence on unsound habits and unjustifiable intuitions. To Kant, an action is morally permissible if and only if its manifestation as a universal is not necessarily contradictory.

The result of applying the categorical imperative to moral dilemmas often coincides with our moral intuitions. It could be argued that the "golden rule", (which most people would intuitively consider moral), is a dumbed down version of the categorical imperative. However, the categorical imperative arises out of logical necessity (infallible), whereas the "golden rule" arises out of intuition.

The Groundwork is not an easy work to digest. The important thing to understand is that Kant was unsatisfied with a morality that depends on how people feel about things, and sought a morality which could stand on its own logical value.


As you said and the quote points out, in Kant's terms, an ethical good act is dictated by the moral law. You do not have to obey the Categorical Imperative, but you will have to if you're aiming at acting morally right. The Categorical Imperative is an idea of an "obligatory ought" ("unbedingtes Sollen"), which is basically a 'must' due to a total lack of alternatives. I do therefore disagree with Sim's comment. The Imperative is not a simple "should".


Kant offers a significant contribution to our discourse on moral philosophy in Metaphysics, with a constellation of principles from his basic starting point--the notion that human beings are rational creatures with an internal will, or "reason"--to conceptual culmination--the pronouncement that to be "moral" is to exercise one's rational capacities in such a way that respects those capacities in other human beings and thus treats these beings as "ends" unto themselves. Using his assertions of the existence of the internal will and its provision of a basis for "pure" moral action (action on the basis of "duty"), Kant defines morality as "the condition under which alone a rational human being can be an end in itself" by his guiding concept: the "categorical imperative," or the exercise of our rational capacities such that we conduct our actions "unconditionally and for their own sake"--in defiance of accessory "inclinations" separate from the internal will.


Kant does not require good will to be rational, to do so would dismiss children and lesser intellects as being incapable of true morality. Then their entire moral lives would be reduced to mere means to our more moral ends, making his moralizing immoral.

He gives rational criteria for validating that one is in accord with true good will. But he does not rule out the idea that a decision can be right without having been intellectually vetted by any specific standard. In fact he makes the point explicitly that simply being in accord with true will, and not motivated by it does not make the action moral.

Since our motivations are perceived with a phenomenal mechanism, the inaccessibility of the noumenal always leaves us guessing whether we have acted on sentiment that is perfectly defensible, or whether we have truly acted out of good will.

From a perspective far outside Kant, one can see that our biology supports an automatic sentiment toward universalizability as much as one toward utilitarianism. I give an argument here: https://philosophy.stackexchange.com/a/17541/9166 which is already too long, so I will not repeat it.

Given that, one might say that what gives this imperative force is our biology being in tune with something deeper.

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