to say, the sciences and the philosophies, as the “guiding thread” of his philosophy of history. II. It does not come within the purpose of this work to give even a summary outline of the philosophy of history developed by Comte first in the _Cours de philosophie positive_, and then in the third volume of the _Politique positive_. Neither shall we disengage the ingenious or profound views of detail with which it abounds. It will suffice for us to show how, according to Comte, the laws of social dynamics are always verified, and how apparent exceptions end by being interpreted in the direction of these laws. Fetichism, properly so-called, was succeeded by astrology, then by polytheism, which was first conservative (the régime of castes in Egypt), then intellectual (Greece), and social (the Roman empire). With the Christian religion monotheism comes to be substituted to polytheism. But does not the theory of progress soon meet with an insurmountable obstacle? How does it explain the Middle Ages, that long succession of centuries which Voltaire and the philosophers had described as full of darkness, of superstition, and of ignorance, as the disgrace of history? How to reconcile this lamentable “retrogression” with the “continuity” of progress affirmed by social dynamics? Auguste Comte’s answer is presented in two forms. In the first place the “retrogression” was never complete. At the time when the Middle Ages were at their darkest in Europe, Arab civilisation was going through its most brilliant period. In it many of the sciences were going beyond the extreme point reached by them in antiquity. The continuity of evolution was then not interrupted. It suffices to understand, in conformity with the postulate laid down by Comte at the beginning of social dynamics, that, at this period, the Arabs were the part of humanity whose intellectual evolution was most advanced, and who, consequently, represented the rest. But, above all, the current opinion concerning the Middle Ages is erroneous. The philosophers of the XVIII. century did not know it. They only saw this period through their prejudices, or rather they did not deign to look at it. Nevertheless, the whole spiritual movement of modern centuries goes back to those “memorable times, unjustly qualified as dark by metaphysical criticism, of which Protestantism was the first organ.”[288]