The differences which separate the historical forms of Christianity are, like those of religion in general, of two kinds: there are differences of kind and differences of degree. The differences of kind are those which arise from diversity of races, languages, civilisations, temperaments, genius. The differences of degree are those connected with the very intensity and purity of the Christian faith and life. Churches and peoples are diversified at once by their constitution and by their degree of culture and of moral life. It goes without saying that these two classes of differences are not juxtaposed; they are mixed incessantly and complicated endlessly. It remains none the less true that they provoke and legitimate two sorts of judgment. The first are accepted with tolerance and sympathy, since it would not be reasonable to blame a man for the colour of his skin. But the second may and should be discussed and analysed, for they imply intellectual errors or moral defects, the corruption or the weakness of the Christian principle, and they can only be corrected and remedied by discussion and criticism. The Christian seed is never sown in a neutral and empty soil. No soul, no social state, is a _tabula rasa_. The place is always occupied by anterior traditions of ideas, rites, or customs, by institutions in possession. Christianity cannot therefore root itself anywhere without entering into conflict with the regnant powers, without giving battle to prejudices, manners, and superstitions which naturally resist, and which, when conquered, spring up again in other forms in the victorious religion. Take the Ebionite Christianity of the first centuries: what is it but a mixture, a compromise between Jewish and Christian elements? What shall we say of the Catholic Church after Constantine? Is it not true that, in the religious transformation at that time effected, there was a double and mutual conversion, and that it is hard to say whether the pagan world was more modified by Christianity or Christianity more deeply penetrated and invaded by the manners and the religion that it was supposed to replace? In this order the most striking victories are never complete. Even after the most radical conversion, the old man survives, at least by its roots, in the new man. The Pharisee long survived in St. Paul after he became an Apostle of Christ. The same in human societies: political or moral revolutions never abolish the past. After those great battles in which passions and interests have often as much weight as noble ideas and generous sentiments, there is always established a sort of equilibrium by mutual concessions and spontaneous alliances between the vanquished and the victorious tendencies. Hence come what we have named the corruptions of the Christian principle in the course of historical Christianity, for which alone should be reserved the name of heresies.