What is the categorical imperative?

It is Kant's supreme moral principle, which commands unconditionally rather than as a means to some further end, and which he states in several formulations including the Formula of Universal Law and the Formula of Humanity.

Why does Kant say moral worth requires acting from duty?

Because, on Kant's view, an action has distinctively moral worth only when it is done out of respect for the moral law itself, not merely from inclination or self-interest that happens to align with duty.

Kantian Ethics

Kantian ethics grounds morality in practical reason, holding that moral requirements are categorical imperatives binding on all rational agents in virtue of their rationality and autonomy.

Definition

Kantian ethics holds that an action has moral worth only if done from duty, and that the supreme principle of morality is the categorical imperative, which commands unconditionally and tests maxims for their fitness to serve as universal laws among autonomous rational agents.

Scope

This topic covers Kant's moral philosophy and its development: the good will and duty, the categorical imperative and its principal formulations, autonomy and the kingdom of ends, and contemporary constructivist readings. It addresses how Kantian ethics derives substantive duties and how it differs from consequentialist and intuitionist deontology.

Core questions

What makes a will good, and how is moral worth related to acting from duty?
How do the formulations of the categorical imperative constrain permissible maxims?
What does it mean to treat humanity always as an end and never merely as a means?
How does autonomy ground the authority of moral law?

Key theories

The Formula of Universal Law: Kant's test that one may act only on a maxim that one can at the same time will to become a universal law, ruling out maxims that cannot be coherently universalized.
The Formula of Humanity: The requirement to treat humanity, whether in oneself or another, always as an end in itself and never merely as a means, grounding respect for persons as the core of morality.

History

Kant set out his moral theory in the Groundwork (1785) and the Critique of Practical Reason (1788), grounding morality in the autonomy of rational agents rather than in inclination or consequences. In the late twentieth century, constructivist interpreters such as Korsgaard (1996) and O'Neill recast the categorical imperative as a procedure for constructing moral requirements from the standpoint of practical reason.

Debates

Rigorism and conflicting duties: Kant's apparent claim that lying is impermissible even to a would-be murderer is taken to show an implausible rigorism; interpreters dispute whether his theory really forbids all exceptions.
The emptiness objection: Hegel and later critics charge that the universal-law test is a merely formal procedure unable to generate determinate duties; defenders reply that it constrains maxims substantively.

Key figures

Immanuel Kant
Christine Korsgaard
Onora O'Neill
Barbara Herman

Seminal works

kant1785
kant1788
korsgaard1996

Frequently asked questions

What is the categorical imperative?: It is Kant's supreme moral principle, which commands unconditionally rather than as a means to some further end, and which he states in several formulations including the Formula of Universal Law and the Formula of Humanity.
Why does Kant say moral worth requires acting from duty?: Because, on Kant's view, an action has distinctively moral worth only when it is done out of respect for the moral law itself, not merely from inclination or self-interest that happens to align with duty.