Benjamin Constant

Benjamin Constant was a French-Swiss political activist and liberal theorist who challenged Kant's absolute prohibition on lying and distinguished ancient from modern liberty.

Constant's essay on the murderer at the door posed the decisive challenge to Kantian absolute duty: if a murderer asks where your friend is hiding, you must lie — demonstrating that consequences cannot be entirely excluded from moral reasoning; he also distinguished the ancient positive liberty of political participation from the modern negative liberty of private life.