The paper gives an interpretation of Kant's doctrine of the fact of reason against the background of a constructivist reading of his philosophy, which does not allow us to appeal to any indubitable facts. The fact of reason is the object of a philosophical account of the moral law forms the quid juris part of deduction or legitimization of the law. A more intuitive grasp of the fact is the phenomenon of reverence for duty which ordinary people grasp in form (...) of a feeling and emotion. (shrink)