Although the origin of a revolution may be perfectly rational, we must not forget that the reasons invoked in preparing for it do not influence the crowd until they have been transformed into sentiments. Rational logic can point to the abuses to be destroyed, but to move the multitude its hopes must be awakened. This can only be effected by the action of the affective and mystic elements which give man the power to act. At the time of the French Revolution, for example, rational logic, in the hands of the philosophers, demonstrated the inconveniences of the ancien regime, and excited the desire to change it. Mystic logic inspired belief in the virtues of a society created in all its members according to certain principles. Affective logic unchained the passions confined by the bonds of ages and led to the worst excesses. Collective logic ruled the clubs and the Assemblies and impelled their members to actions which neither rational nor affective nor mystic logic would ever have caused them to commit. Whatever its origin, a revolution is not productive of results until it has sunk into the soul of the multitude. Then events acquire special forms resulting from the peculiar psychology of crowds. Popular movements for this reason have characteristics so pronounced that the description of one will enable us to comprehend the others. The multitude is, therefore, the agent of a revolution; but not its point of departure. The crowd represents an amorphous being which can do nothing, and will nothing, without a head to lead it. It will quickly exceed the impulse once received, but it never creates it. The sudden political revolutions which strike the historian most forcibly are often the least important. The great revolutions are those of manners and thought. Changing the name of a government does not transform the mentality of a people. To overthrow the institutions of a people is not to re-shape its soul. The true revolutions, those which transform the destinies of the peoples, are most frequently accomplished so slowly that the historians can hardly point to their beginnings. The term evolution is, therefore, far more appropriate than revolution. The various elements we have enumerated as entering into the genesis of the majority of revolutions will not suffice to classify them. Considering only the designed object, we will divide them into scientific revolutions, political revolutions, and religious revolutions. 2. Scientific Revolutions. Scientific revolutions are by far the most important. Although they attract but little attention, they are often fraught with remote consequences, such as are not engendered by political revolutions. We will therefore put them first, although we cannot study them here.