“Consciousness of this fundamental law may be called a fact of reason.”Immanuel Kant · Critica rațiunii practice · 1788 · Partea I, Cartea I, §6, AA 5:31
The moral law is not proven but observed: denying it already affirms it.
Kant seeks an unshakable starting point for ethics and finds it not in arguments but in the fact that every person is aware of duty, even when violating it. This awareness works like a fact: it cannot be denied without affirming it, since denying it is itself a moral judgment. Anyone claiming no binding rules exist is already making excuses, and thus acknowledging obligation.
If duty is something observed, not a proven conclusion, then the order of thinking changes. We do not build morality starting from interests or consequences. We find it already active in us, the way we find that we think. Someone recalling a lie told yesterday feels that unwanted weight before analyzing anything. That feeling is not the result of a calculation, but of a law we did not write ourselves. From here a natural question arises: what kind of law is this, and where does its authority over us come from?
Why it matters For anyone wondering why morality is not just opinion, the answer is that the sense of duty is directly observable, prior to any theory.