No More Learning

All           is known only by the obstacles that it can overcome; and in the case of virtue the obstacles are the natural inclinations which may come into conflict with the moral purpose; and as it is the man who himself puts these obstacles in the way of his maxims, hence virtue is not merely a self-constraint (for that might be an effort of one inclination to constrain another), but is also a con- straint according to a principle of inward freedom, and therefore by the mere idea of duty, according to its formal law.