To those who hold that experience mechanically impresses itself upon the mind and so automatically expresses itself as truth, it must appear somewhat strange that mankind should have advanced for thousands of years without knowing that they had progressed; and still more strange that it was not as an induction from experience, but on _a priori_ grounds that they arrived at the conclusion. Yet so it was. The mere contemplation of the rise and fall of empires no more suggested the presence and persistence of a constant tendency to progress than the mountainous wave which threatens to engulf the ship suggests that the sea-level is a scientific truth. But when Darwin established his theory that man was descended from the brute, all was clear: it became certain _a priori_ that the long history and "pre-history" of man must have been one of progress and advance. When the descent of man was established, his ascent came to be studied, and human evolution was seen to be synonymous with progress. Savages were seen to be the nearest existing representatives of primitive man, and there was an end to the idea that the primitive state was perfection. The comparative method, once applied to the study of mankind, was able to set side by side examples of savagery, barbarism, and civilisation, which illustrated every step in the process of the evolution of society, and showed that, though the forms of society may fluctuate as do the waves of the sea, society itself is steady in its advance and progressive in its evolution. This conclusion, which at first was a deduction drawn from the animal descent of man, has now the independent support of an enormous amount of evidence. The existence of a Stone Age, palæolithic and neolithic, of a Bronze Age and an Iron Age, and the succession of those ages in the order named, are established facts of science. That the culture of nomad peoples is lower than that of pastoral tribes; that pastoral tribes advance in culture when they become agricultural; that agriculture, implying settled habits and fixed homes, leads to the foundation of cities and the formation of civic life; that the city-states of the ancient world give way to the nation-states of modern times: are all accepted facts, bridging the apparent chasm between civilisation and savagery, and demonstrating the action of the law of continuity in the evolution of society.