But most unfortunately for the Mu‘tazilites and for Islam, a Khalifa arose who had a relish for theological discussions and a high opinion of his own infallibility. This was al-Ma’mun. It did not matter that he ranged himself on the progressive side; his fatal error was that he invoked the authority of the state in matters of the intellectual and religious life. Thus, by enabling the conservative party to pose as martyrs, he brought the prejudices and passions of the populace still more against the new movement. He was that most dangerous of all beings, a doctrinaire despot. He had ideas and tried to make other people live up to them. Al-Mansur, though a bloody tyrant, had been a great statesman and had known how to bend people and things quietly to his will. He had sketched the firm outlines of a policy for the Abbasids, but had been cautious how he proclaimed his programme to the world. The world would come to him in time, and he could afford to wait and work in the dark. He knew, above all, that no people would submit to be school-mastered into the way in which they should go. Al-Ma’mun, for all his genius, was at heart a school-master. He was an enlightened patron of an enlightened Islam. Those who preferred to dwell in the darkness of the obscurant, he first scolded and then punished. Discussions in theology and comparative religion were his hobby. That some such interchange of letters between Muslims and Christians as that which crystallized in the Epistle of al-Kindi took place at his court seems certain. Bishr al-Marisi, who had lived in hiding in ar-Rashid’s time on account of his heretical views, disputed, in 209, before al-Ma’mun on the nature of the Qur’an. He founded at Baghdad an academy with library, laboratories, and observatory. All the weight of his influence was thrown on the side of the Mu‘tazilites. It appeared as though he were determined to pull his people up by force from their superstition and ignorance.