The spirit of inquiry, which always leads men to question the authority of these customs and moral codes and of their religious sanctions and thus tends to weaken them, is, then, a socially disruptive force, at the same time that it is the source of all progress. Hence, though the free play of the intellect and of the spirit of inquiry may secure for a time the rapid progress of civilisation, it cannot alone secure continued progress. Continued progress has only resulted where there has been maintained a happy balance between the conservative and the progressive forces, between the authority of custom and the moral code on the one hand and the free activity of the intellect on the other. Wherever the progressive force has outrun the conservative, progress has been first rapid and then has come abruptly to an end. Greece exemplified this process in the clearest manner. It was the excessive seeking of individuals for their own power and glory, unrestrained by the customs and religious systems which their intellect had outgrown, that ruptured the bonds of society, plunged the State into war and civil strife, and eventually destroyed it by the extermination of the Greek aristocracy. The same is true of the brilliant but brief periods of rapid progress exhibited by the medieval Italian States. Intellect outran and undermined morals, and progress was brought to an end. Some observers have maintained that history will pass the same verdict upon modern France, and that most of our leading nations of the present day are seriously threatened by the same danger. Any long continued progressive evolution of the mind of a people has been, then, a rare exception in the history of the world; partly because the free play of the spirit of inquiry and of the intellectual faculties, which is the source of all progress, exerts a socially disruptive tendency, so that progress is by its very nature dangerous to the stability of any nation; but partly also because the free play of the spirit of inquiry has been so rarely achieved or permitted, so that even such progress as has led on to social disruption has been exceptional. A long period of intellectual and moral stagnation in the rigid bonds of custom and religion has been the rule for nearly all the peoples of the earth, so soon as they had attained to a settled mode of existence. The primary question, then, to be answered in seeking to account for the progress of nations, is—What conditions enabled the spirit of inquiry to break the bonds of custom and religion and to extend man’s knowledge of man and of the world in which he lives?