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.
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 become a necessity, then it is not a habit proceeding from freedom, and therefore not a moral habit. Virtue therefore cannot be defined as a habit of free law-abiding actions, unless indeed we add "determining itself in its action by the idea of the law"; and then this habit is not a property of the elective will, but of the rational will, which is a faculty that in adopting a rule also declares it to be a universal law, and it is only such a habit that can be reckoned as virtue. Two things are required for internal freedom: to be master of oneself in a given case (animus sui compos) and to have command over oneself (imperium in semetipsum), that is to subdue his emotions and to govern his passions. With these conditions, the character (indoles) is noble (erecta); in the opposite case, it is ignoble (indoles abjecta serva).