I have stated this problem almost in Kant's words, and as he might have stated it if he had not introduced the conception of final causes. His use of the postulate of final causes without justifying it is a defect in his essay. He identifies what he well calls a stream of tendency with "a natural purpose." He makes no attempt to show that the succession of events is such that it cannot be explained without the postulate of a purpose. His solution of the problem is governed by this conception of finality, and by the unwarranted assumption that nature does nothing in vain.
He lays down that all the tendencies to which any creature is predisposed by its nature must in the end be developed perfectly and agreeably to their final purpose. Those predispositions in man which serve the use of his reason are therefore destined to be fully developed. This destiny, however, cannot be realised in the individual; it can only be realised in the species. For reason works tentatively, by progress and regress. Each man would require an inordinate length of time to make a perfect use of his natural tendencies. Therefore, as life is short, an incalculable series of generations is needed.
The means which nature employs to develop these tendencies is the antagonism which in man's social state exists between his gregarious and his antigregarious tendencies. His antigregarious nature expresses itself in the desire to force all things to comply to his own humour. Hence ambition, love of honour, avarice. These were necessary to raise mankind from the savage to the civilised state. But for these antisocial propensities men would be gentle as sheep, and "an Arcadian life would arise, of perfect harmony and mutual love, such as must suffocate and stifle all talents in their very germs." Nature, knowing better than man what is good for the species, ordains discord. She is to be thanked for competition and enmity, and for the thirst of power and wealth. For without these the final purpose of realising man's rational nature would remain unfulfilled. This is Kant's answer to Rousseau.
The full realisation of man's rational nature is possible only in a "universal civil society" founded on political justice. The establishment of such a society is the highest problem for the human species. Kant contemplates, as the political goal, a confederation of states in which the utmost possible freedom shall be united with the most rigorous determination of the boundaries of freedom.
Is it reasonable to suppose that a universal or cosmopolitical society of this kind will come into being; and if so, how will it be brought about? Political changes in the relations of states are generally produced by war. Wars are tentative endeavours to bring about new relations and to form new political bodies. Are combinations and recombinations to continue until by pure chance some rational self-supporting system emerges? Or is it possible that no such condition of society may ever arrive, and that ultimately all progress may be overwhelmed by a hell of evils? Or, finally, is Nature pursuing her regular course of raising the species by its own spontaneous efforts and developing, in the apparently wild succession of events, man's originally implanted tendencies?
Kant accepts the last alternative on the ground that it is not reasonable to assume a final purpose in particular natural processes and at the same time to assume that there is no final purpose in the whole. Thus his theory of Progress depends on the hypothesis of final causes.
It follows that to trace the history of mankind is equivalent to unravelling a hidden plan of Nature for accomplishing a perfect civil constitution for a universal society; since a universal society is the sole state in which the tendencies of human nature can be fully developed. We cannot determine the orbit of the development, because the whole period is so vast and only a small fraction is known to us, but this is enough to show that there is a definite course.
Kant thinks that such a "cosmopolitical" history, as he calls it, is possible, and that if it were written it would give us a clew opening up "a consolatory prospect into futurity, in which at a remote distance we shall discover the human species seated upon an eminence won by infinite toil, where all the germs are unfolded which nature has implanted and its own destination upon this earth accomplished."
3.
But to see the full bearing of Kant's discussion we must understand its connection with his ethics. For his ethical theory is the foundation and the motive of his speculation on Progress. The progress on which he lays stress is moral amelioration; he refers little to scientific or material progress. For him morality was an absolute obligation founded in the nature of reason. Such an obligation presupposes an end to be attained, and this end is a reign of reason under which all men obeying the moral law mutually treat each other as ends in themselves. Such an ideal state must be regarded as possible, because it is a necessary postulate of reason. From this point of view it may be seen that Kant's speculation on universal history is really a discussion whether the ideal state, which is required as a subjective postulate in the interest of ethics, is likely to be realised objectively.