display themselves in common with unwonted vigor; if we consider that Christianity and Buddhism were developed at periods of grand systematizations and in the midst of sufferings like the oppression which stirred up the fanatics of Cevennes; if, on the other hand, it is recognized that primitive religions are born at the dawn of human reason, during the richest expansion of human imagination, at times of the greatest naivete and of the greatest credulity; if we consider, again, that Mohammedanism appeared along with the advent of poetic prose and of the conception of material unity, amongst a people destitute of science and at the moment of a sudden development of the intellect—­we might conclude that religion is born and declines, is reformed and transformed, according as circumstances fortify and bring together, with more or less precision and energy, its three generative instincts; and we would then comprehend why religion is endemic in India among specially exalted imaginative and philosophic intellects; why it blooms out so wonderfully and so grandly in the Middle Ages, in an oppressive society, amongst new languages and literature; why it develops again in the sixteenth century with a new character and an heroic enthusiasm, at the time of an universal renaissance and at the awakening of the Germanic races; why it swarms out in so many bizarre sects in the rude democracy of America and under the bureaucratic despotism of Russia; why, in fine, it is seen spreading out in the Europe of to-day in such different proportions and with such special traits, according to such differences of race and of civilizations.  And so for every kind of human production, for letters, music, the arts of design, philosophy, the sciences, state industries, and the rest.  Each has some moral tendency for its direct cause, or a concurrence of moral tendencies; given the cause, it appears; the cause withdrawn, it disappears; the weakness or intensity of the cause is the measure of its own weakness or intensity.  It is bound to that like any physical phenomenon to its condition, like dew to the chilliness of a surrounding atmosphere, like dilatation to heat.  Couples exist in the moral world as they exist in the physical world, as rigorously linked together and as universally diffused.  Whatever in one case produces, alters, or suppresses the first term, produces, alters, and suppresses the second term as a necessary consequence.  Whatever cools the surrounding atmosphere causes the fall of dew.  Whatever develops credulity, along with poetic conceptions of the universe, engenders religion.  Thus have things come about, and thus will they continue to come about.  As soon as the adequate and necessary condition of one of these vast apparitions becomes known to us our mind has a hold on the future as well as on the past.  We can confidently state under what circumstances it will reappear, foretell without rashness many portions of its future history, and sketch with precaution some of the traits of its ulterior development.