In the history of human thought and social organization there is an interesting pendular swing between conflicting ideas so that, about the time we wake up to recognize that thought is swinging one way, we may be fairly sure that soon it will be swinging the other. Man's social organization, for example, has moved back and forth between the two poles of individual liberty and social solidarity. To pick up the swing of that pendulum only in recent times, we note that out of the social solidarity of the feudal system man swung over to the individual liberty of the free cities; then from the individual liberty of the free cities to the social solidarity of the absolute monarchies; then back again into the individual liberty of the democratic states. We see that now we are clearly swinging over to some new form of social solidarity, of which tendency federalism and socialism are expressions, and doubtless from that we shall recoil toward individual liberty once more. It is a safe generalization that whenever human thought shows some decided trend, a corrective movement is not far away. However enthusiastic we may be, therefore, about the idea of progress and the positive contributions which it can make to our understanding and mastery of life, we may be certain that there are in it the faults of its qualities. If we take it without salt, our children will rise up, not to applaud our far-seeing wisdom, but to blame our easy-going credulity. We have already seen that the very idea of progress sprang up in recent times in consequence of a few factors which predisposed men's minds to social hopefulness. Fortunately, some of these factors, such as the scientific control of life through the knowledge of law, seem permanent, and we are confident that the idea of progress will have abiding meaning for human thought and life. But no study of the matter could be complete without an endeavour to discern the perils in this modern mode of thought and to guard ourselves against accepting as an unmixed blessing what is certainly, like all things human, a blend of good and evil.