Categorical imperative
The categorical imperative is the cornerstone of Immanuel Kant's deontological moral philosophy, articulated in his 1785 treatise Groundwork of the Metaphysics of Morals, as an a priori principle of practical reason that unconditionally obligates rational agents to act in ways consistent with universal moral laws, detached from empirical consequences, personal inclinations, or hypothetical ends.[1][2] It demands adherence to maxims that could coherently apply to all rational beings without contradiction, thereby establishing duty as the sole determinant of moral worth.[1] Kant contrasts the categorical imperative with hypothetical imperatives, which condition actions on achieving desired outcomes, such as "if you wish to be healthy, exercise," rendering them advisory rather than binding.[1] The imperative's formulations include the formula of universal law—"Act only according to that maxim whereby you can at the same time will that it should become a universal law"—which tests moral permissibility by assessing whether a proposed action's underlying principle could consistently govern all similar cases without logical inconsistency or self-defeat.[1][3] A second formulation requires treating humanity, whether in oneself or others, always as an end in itself and never merely as a means, emphasizing respect for rational autonomy. These principles underpin Kant's conception of a "kingdom of ends," where rational agents legislate and obey moral laws in mutual respect.[1] While the categorical imperative has profoundly shaped modern ethical theory by prioritizing rational duty over consequentialism, it faces critiques for its apparent inflexibility, such as prohibiting deception even to thwart harm, as in Kant's example of denying refuge to a murderer at the door, and for presuming universal rationality among moral agents, potentially excluding non-rational entities or impaired individuals.[4][5][6]