The theoretic backbone of this mental attitude was the doctrine of the Fathers of the Church and the older scholasticism, pronouncing the illimitable power of human perception; the world's profoundest depths had been fathomed, its riddle finally solved; there was consequently no room for philosophy, the endless meditation on the meaning of the world and the destiny of man. Science had but one task: to bring logical proof of the revealed religious verities. The greatest champion of this view was Anselm of Canterbury (1033-1109), who in his treatise, _Cur Deus Homo_ proved that God was compelled to become man in order to complete the work of salvation. Abélard preached a similar doctrine, but carried away by the fervour of thought, arrived at conclusions which he was forced to recant ignominiously; for at the end of his chain of evidence he did not always find the foregone conclusion which should have been there. This system of a final and infallible knowledge of the world is the very foundation of ecclesiastical government. The priest alone has all knowledge, for he has the doctrine of salvation. Had it occurred to any man to defend his own opinions in contradiction to the system of the Church, that man would speedily have come to the conclusion that the devil had tempted him to false observations, or false deductions, and his submission to the Church would have been the outward sign of his victory over the evil which had blinded his spiritual vision. A man had to choose between the worship of God and the worship of the devil, there was no alternative. Nobody knew the limits of human knowledge; everybody, the learned ecclesiastic as well as the unlearned, plain man, believed others to be in possession of the key to profound secrets and unlimited power. One thing only was needful: to possess one's self of the philosopher's stone; therefore the belief in witchcraft and the fear of certain men supposed to be endowed with supernatural power--the priests--were but the obvious results of a world-system, founded on a revealed and exact religion.