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.
Remarks
Of the Doctrine of Virtue on the Principle Of Internal Freedom.

Habit (habitus) is a facility of action and a subjective perfection of the elective will. But not every such facility is a free habit (habitus libertatis); for if it is custom (assuetudo), that is, a uniformity of action which, by frequent repetition, has beco............