Hence this internal
which is the condition of all ethical duty must be discussed as a preliminary (discursus praeliminaris), just as above the doctrine of conscience was discussed as the condition of all duty.
The-Critique-of-Practical-Reason-The-Metaphysical-Elements-of-Ethics-and-Fundamental-Principles-of-the-Metaphysic-of-Morals-by-Immanuel-Kant
