This "comprehension" is not merely one of breadth, but of depth as well: the ideal includes not only the present of mankind, but its whole future also. Duties have always been recognized to posterity, but the range of generations to whom they applied was small, and the interests which it was believed could be secured were limited also. _Apres moi le deluge_ describes a form of selfishness of all ages, but different ages have understood the _apres moi_ quite differently. At the present day, the range of responsibility is extending indefinitely. A common political ideal does not mean a universal peace. Coarser forms of dispute disappear, but, on the other hand, as nations grow more refined in their ideals, they grow more susceptible. What a political humanity, or a political community of Europe, would mean, is the substitution of international punishment for the self-willed conflicts of irresponsible nations. We cannot say what the future of society and of morality may be,--whether mankind will be able to take mechanical means against a period of ice, or whether human society may not, as a whole, be destroyed, to be replaced by a higher type of existence, which may arise on the earth from the development of humanity, or may, on some other planet, take up the tale of human civilization as we take up that of the civilization of Greece and Rome. Two things follow from the progressive character of the moral ideal: (1) that the classification and description of duties will vary with each age; (2) that, as the ideal changes from age to age, the highest moral principle or sentiment will change with it.