XV Of the Principle on Which Ethics Is Separated From Jurisprudence
This separation on which the subdivision of moral philosophy in general rests, is founded on this: that the notion of freedom, which is common to both, makes it necessary to divide duties into those of external and those of internal freedom; the latter of which alone are ethical. Hence this internal freedom 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.
INTRODUCTION ^paragraph 185