Pravo na laganje

This 1797 discussion begins with Constant's critique of Kant in his essay Des réactions politiques: an absolute duty to tell the truth, if applied unconditionally, would destroy society. Constant gives an example: if a murderer asks about a friend who has hidden in your house, lying would be justified out of philanthropy – because the murderer has no right to the truth.

Kant responds strongly, defending the absolute prohibition of lying. Kant's key arguments:

• The expression "right to the truth" is meaningless – there is no objective right to the truth, but only a subjective duty of truthfulness (veracitas) towards oneself and others.
• A lie is a deliberate untruth in a statement to another – it does not depend on harm, but on the violation of a formal duty of reason.
• The duty to tell the truth is categorical, without exceptions – the basis of all contracts, trusts and rights. If an exception is allowed (e.g. out of love for one's neighbor), the maxim becomes non-universal: the world would collapse into a chaos of distrust.
• In Constant's example: if you lie to a murderer, you are violating your duty – even if you do not accidentally harm him, lying is a crime against reason. If the murderer forces you to make a statement, the lie is a falsiloquium (untruth), but still a violation – you are responsible for the consequences if the lie enables the crime.

Kant does not allow "white lies" out of humanity – truthfulness is a sacred commandment of reason, of unlimited benefit. Constant sees this as a rigidity that destroys society; Kant sees Constant's approach as opportunism that undermines the foundation of morality.

This debate – one of the most famous in ethics – shows the conflict between absolute deontologism and pragmatic consequentialism.