Kant's Duty Ethics

by Dr. Jan Garrett

Last revised: October 2, 2006

For a very substantial internet resource center on Kant, see Kant on the Web.

For the text from which the ideas discussed below are primarily derived see
Immanuel Kant, Fundamental Principles of the Metaphysics of Morals (complete text, pdf file)

For Kant, the morally important thing is not consequences but the way choosers think when they make choices.

Kant says that only one [kind of] thing is inherently good, and that is the good will.

What makes the will good? The will is good when it acts out of duty, not out of inclination.

What does it mean to act out of inclination? To do something because it makes you feel good or because you hope to gain something from it.

What does it mean to act out of duty? Kant says this means that we should act from respect for the moral law.

How do we do that? We must know what the moral law is.

How do we know that? We use the "Categorical Imperative."


Act only on those maxims (or rules of action)
that you could at the same time will to be a universal law.

The Categorical Imperative is a rule for testing rules.

Kant's example of a false promise (Using Test One)

Maxim: I may make a false promise in order to reap financial gain.

Generalized: Anyone may make a false promise to get something s/he wants.

This is self-contradictory because:

If anyone may make a "false promise," nobody would take a promise seriously; promising becomes meaningless.

Result: I may not act on that maxim.

The maxim fails Test One.

Similar reasoning leads Kant to conclude that any maxim permitting theft or lying must be rejected.

A thief's maxim, once generalized, would overturn the institution of property, but unless the institution of property exists, there can be no theft.

A liar's maxim, once generalized, would overturn the assumption of truthfulness, but without this assumption, no lie can even be attempted.

Kant's example of the Bad Samaritan (Using Tests One and Two)

Maxim: I may refuse to help another person in distress who cannot pay me even though I could do so at little cost to myself.

Generalized: Anyone may refuse to help another person in distress who cannot pay her even though it would cost her little to help.

Can it be conceived? Yes.

Could you will this to be a universal law? Probably not, because you might find yourself in a situation of extreme need and nobody else would help you.

Result: You cannot act on the "Bad Samaritan" maxim.

Try this method on a maxim that would permit you to dump your used motor oil on the ground in order to save time and effort rather than taking it to an oil recycling center.


Always act so as to treat rational nature
(i.e., other human beings) as an end, never as a means only.

The phrase "practical imperative" is Jacques Thiroux's. Kant himself says this is just another way of stating his Categorical Imperative.

This version of the Categorical Imperative seems designed to exclude exploitation. Utilitarianism has been accused of justifying exploitation of people already disadvantaged. If a program increases the misery of the disadvantaged but promotes the total social good, then utilitarianism might have to support such a program.