Three classes of actions to which public opinion applies its sanction may be distinguished: actions blamed; those the neglect of which is blamed; and those which are praised. The first two classes, sanctioned by a punishment, are regarded as duty; the last class, sanctioned by at least mental reward, are actions of desert. Actions the omission of which is punished or blamed are not actions of desert, but of duty and obligation. The boundary-line between duty and desert is not fixed and definite; in the measure in which the moral condition of a society is perfected, the province of that which is regarded as duty is extended into that which was formerly regarded as desert. The distinction between duty and desert has, in general, only an outward significance; it has regard to the relation to others, to the social sanction. The moral human being does not inquire what entitles him to praise, but simply what is right; and he does not compare himself with others but with his moral ideal. Hence he recognizes, with regard to himself, only duty, not desert. He aspires to attain, not the approbation of others, but his own, and he attains this only when he has done that which he holds to be the best possible. The moral significance of the outward sanction lies in its educating influence; it acts as counterpoise to inclination to action opposed to the moral law, and facilitates, thus, the victory of the moral motives, which increase in strength through use. If it is true that a condition of "heteronomy" always precedes that of "autonomy," then the outer sanction is the indispensable condition of the evolution of moral feelings. It has sometimes been said that the human being is under obligation to others only. But it seems that this view has proceeded from a confusion of the moral with the juridic significance of the word "duty." It is not to be doubted that the consciousness of duty would not develop in an individual who grew up in solitude,--but speech and reason likewise would not become his. The law of morality applies not only to social conduct but also to conduct having reference to self. By "moral law" is not meant a law in the sense that it is imposed on human beings from without, by another; it is exactly the peculiarity of the moral law that it is self-imposed as the voice of conscience. Virtue is related to duty as the enduring characteristic to the single action, or the lasting will to obligation, to the "ought"; virtue is a disposition to act in accordance with duty. Vice is a characteristic which continually determines actions opposed to duty.