Kant's Categorical Imperative
The Categorical Imperative is Kant's supreme principle of morality, the single rule from which all genuine moral obligations derive, formulated in three equivalent versions: (1) the Universal Law Formula (act only according to maxims you could will to be universal laws); (2) the Humanity Formula (treat humanity, whether in your own person or that of another, always as an end and never merely as a means); and (3) the Kingdom of Ends Formula (act as a legislating member of a universal community of rational beings), establishing that moral obligations are binding independently of consequences or desires, purely from the form of rational consistency.
Kant's ethical project in the Groundwork for the Metaphysics of Morals (1785) began with a diagnosis: every previous ethical theory derived morality from something outside morality itself, from consequences (pleasure, happiness, welfare), from divine command, from natural instincts. Kant argued this was a fundamental error. A genuinely moral obligation must be unconditional, binding regardless of consequences, circumstances, or inclinations. The only source of unconditional obligation is pure practical reason: the capacity of rational beings to give themselves laws based on rational consistency alone.
The Universal Law Formula captures the core insight: before acting, ask whether the principle (maxim) behind your action could be consistently universalized, whether you could will that all rational beings act on the same principle. The lying promise test is the classic example: could you universalize the maxim 'I will make a false promise when convenient'? No, because if everyone made false promises, the institution of promising would dissolve, making the very action (promise-making) impossible. The self-defeating character of the universal principle reveals the immorality of the individual action. Kant argues this is not consequentialist reasoning (we don't reject lying because it has bad consequences) but purely formal: the maxim contradicts itself when universalized.
The Humanity Formula is the most practically significant: never treat a person merely as a means to your ends but always also as an end in themselves. This provides the foundation for human rights theory, persons have a dignity (Würde) that cannot be traded off against any amount of welfare or utility. Predictive History connects Kant's categorical imperative to the Enlightenment worldview's claim of universal human dignity: Kant provides the philosophical machinery for deriving this claim from pure reason rather than theological assertion, making it (apparently) independent of Christian metaphysics. The secular human rights tradition runs directly through Kant's Humanity Formula.
Related articles
Related terms
Frequently asked questions
What is Kant's categorical imperative? ＋
The supreme moral principle: act only according to maxims you could will to be universal laws. The lying promise test: could you universalize 'I will make false promises when convenient'? No, if everyone did, promising would be impossible, making the action self-defeating. Three formulations: (1) Universal Law Formula; (2) Humanity Formula, never treat persons merely as means, always as ends; (3) Kingdom of Ends, act as a member of a universal rational community. Moral obligations are binding independently of consequences, purely from rational consistency.