The positive philosophy of history takes as its guiding principle the idea of unity. In virtue of a postulate which is an audacious anticipation concerning an uncertain future, the human species, in it, is regarded as an immense social unity. Similarly, in it, the evolution of humanity is regarded as ending in the moral and religious unity of all men. Humanity goes from spontaneous religion where it begins, to demonstrated religion where it becomes finally established. Between the two lies the domain of history. The successive states through which humanity passes in evolving are not homogeneous. The theological and the positive spirit are mingled in them at various degrees. They struggle one against the other. These states then contain within themselves the principle of their own destruction. Each one necessarily prepares the appearance of the following one, until the final state in which the positive spirit alone will predominate. The spring of these concrete views of history is the logical need of unity. It is this which determined the initial movement. For the primitive religions, unity was never perfect. Even at the period when fetichism rules without question, some rudiments of the positive spirit exist. Human nature, being invariable, the germ of its final state was already contained in a primitive state. From that time it was certain that, if humanity emerged from its primitive state, it would evolve until it found unity in the final religion. If this be so, how is it that Comte did not regard the succession of religious forms as the supreme dynamic law, as the principle of the philosophy of history? Why did he believe rather that he had found this principle in the law of the evolution of philosophies? It is because, according to him, the evolution of religious forms is a function of intellectual evolution. It is even subordinate to intellectual evolution, in this sense, that progress in the knowledge of the laws of nature sooner or later brings about a religious revolution. In the second place, if the philosophy of history had chosen the succession of religious forms as its chief axis, it would only have studied the process of decomposition of beliefs, which, up to the present time, has led them from the period when all thought is religious (fetichism), to that when no thought seems to be so any more (philosophical deism). It would not show at the same time the inverse and simultaneous process of the positive spirit, which not only determines this progressive decomposition, but also prepares the elements of a new faith. It would not show how by degrees, by means of science, this spirit establishes a conception of nature which by becoming social will become universal, and which will be the basis of the final religion. This is why Comte, while making religion the chief element in individual and social human life, was nevertheless to take the evolution of the intellect, that is