Increasingly, from this time on, it is not heresy which has to be met so much as simple unbelief, more or less frank. It is evident that the heretics of the earlier period are now dividing in two directions, one part inclining toward milder forms of heresy and the other toward doubt in the largest sense, passing over to Aristotelian + neo-Platonic philosophy, and thence dividing into materialists, deists, and theists. Thus we have seen earlier the workings of al-Farabi and of the Ikhwan as-safa. The teachings of the latter pass on to the Isma‘ilians who developed them in the mountain fortresses, the centres of their power, scattered from Persia to Syria. These were otherwise called Assassins; otherwise Batinites in the narrower sense—in the broader that term meant only those who found under the letter of the Qur’an a hidden, esoteric meaning; otherwise Ta‘limites or claimers of a _ta‘lim_, a secret teaching by a divinely instructed Imam, and with them we shall have much to do later. It is sufficient here to notice how the peaceful and rather watery philosophy of the “Sincere Brethren” was transmuted through ambition and fanaticism into belligerent politics at the hands and daggers of these fierce sectaries. Into this period, too, fall some well-known names of dubious and more than dubious orthodoxy. Al-Beruni (d. 440) even at the court of Mahmud of Ghazna managed to keep his footing and his head. Yet it may be doubted how far he was a Karramite or even a Muslim. He was certainly the first scientific student of India and _Indica_ and of chronology and calendars, a man whose attainments and results show that our so-called modern methods are as old as genius. On religion, he maintained a prudent silence, but earned the favor of Mahmud by an unsparing exposure of the weakness in the Fatimid genealogy. In this sketch he has a place as a man of science who went his own way without treading on the religious toes of other people.