Kantian ethics

The core idea

Immanuel Kant held that the only thing good without qualification is a good will: acting from duty, because it is right, not from inclination or for some benefit. The moral worth of an action lies in the principle behind it, not its results.

The test of a principle is the categorical imperative. Could you will that everyone act on it? A lying promise fails, because if everyone made them, promises would mean nothing. And you must treat humanity, in yourself and others, always as an end and never merely as a means. This gives persons a dignity that cannot be traded off against benefits to others.

Kantian ethics is the leading form of deontology. It shapes modern ideas of human rights, consent and respect, and supplies the main objections to utilitarianism in cases such as the trolley problem.

What they hold

• Moral rules bind all rational beings, whatever their desires.
• Act only on principles you could will to be universal laws.
• Never treat a person merely as a means to an end.
• The rightness of an act does not depend on its consequences.
• Morality presupposes that we are free.

The main criticisms

The classic objection is rigidity: Kant held that it is wrong to lie even to a murderer asking where your friend is hiding. Critics also argue that the universalisability test can approve bad principles and reject harmless ones, and that the theory has trouble when duties conflict. Utilitarians reply that refusing to minimise harm is a strange kind of respect.

“Two things fill the mind with ever new and increasing admiration and awe, the oftener and the more steadily we reflect on them: the starry heavens above and the moral law within.”

Immanuel Kant, Critique of Practical Reason, trans. T. K. Abbott

Further reading

• EncyclopediaStanford Encyclopedia of Philosophy: Kant's Moral Philosophy
• WikipediaKantian ethics