Kant, l'assassino alla porta e il giudizio morale comune

In 1797, Kant asserted a thesis that Benjamin Constant had polemically attributed to a German philosopher: we are not allowed to lie, not even to a murderer who asks us whether a friend of ours who is being pursued by him has taken refuge in our house. Kant's answer to the dilemma of the murderer at the door, which rules out the possibility of any exceptions to the duty of truthfulness, seems counterintuitive and difficult to reconcile with Kant's thesis that common moral judgement is reliable. For Kant, the task of the moral philosopher is a conceptual analysis of existing morality, and philosophy has nothing to say about normative ethics other than, or in addition to, what the common man already knows. The paper traces the real subject of the discussion between Kant and Constant and presents the conception that leads Kant to reject the dilemma of the murderer at the door as unrealistic. Kant believes that the course of the world and the choices of moral subjects cannot be objects of calculation, prediction and control and therefore, like his contemporaries, assumes two dimensions, as constitutive of moral life, of which the overriding one imposes prohibitions whose observance is always in the power of everyone.