What, then, is the law of human progress—the law under which civilization advances?

It must explain clearly and definitely, and not by vague generalities or superficial analogies, why, though mankind started presumably with the same capacities and at the same time, there now exist such wide differences in social development. It must account for the arrested civilizations and for the decayed and destroyed civilizations; for the general facts as to the rise of civilization, and for the petrifying or enervating force which the progress of civilization has heretofore always evolved. It must account for retrogression as well as for progression; for the differences in general character between Asiatic and European civilizations; for the difference between classical and modern civilizations; for the different rates at which progress goes on; and for those bursts, and starts, and halts of progress which are so marked as minor phenomena And, thus, it must show us what are the essential conditions of progress, and what social adjustments advance and what retard it?

It is not difficult to discover such a law. We have but to look and we may see it. I do not pretend to give it scientific precision, but merely to point it out.