During the tenth and eleventh centuries when Christendom was for the most part wrapped in a barbarous ignorance, Saracen culture, in the caliphates of Baghdad and Cordova, had kept alive the sciences—mathematics, astronomy, medicine—and speculative thinkers had preserved, not indeed uncorrupted, yet always as a vital influence, the ancient philosophy of Greece, when to the Christian world it was lost in oblivion. Side by side with an orthodox philosophy in consonance with the teachings of the Koran, Islam had produced a heretic philosophy, which though written in a Semitic language and modified by an oriental environment, was essentially Greek, essentially Aristotelian.[73] To the Arabian thinkers the Stagirite represented the utmost limit of the human intelligence; they could not conceive that there could ever be improvement upon knowledge so Catholic, synthesis so complete. The first of the great Arabian philosophers, Alfarabi, had been Neoplatonist in thought, Aristotelian in method.[74] His great successor, Avicenna, was Aristotelian both in the content and the logical scheme of his work.[75] The distinctive teachings of Avicenna were, first, the nominalist doctrine that universality exists not in reality, but in thought only; secondly, that matter is uncreated and eternal; thirdly, that the first and only direct emanation from God or the First Cause is Intelligence, νοῦς, but that this communication of intelligence to lesser beings is not a single act in time, but a constant process or an everlasting act. While in the eastern caliphate these bold speculations were strongly denounced by the later philosopher of Baghdad, Ghazali, and were repudiated in a powerful orthodox reaction;[76] in Spain at the beginning of the twelfth century Avempace and Abubacer were teaching that the life of the soul is a progress from a purely instinctive existence shared with the lower animals to a spiritual absorption in the divine essence and intellect; while the latter philosopher added the contention that religious creeds were but types of, or approximations to, absolute truth, which the philosopher, but never the mere theologian, may attain. The greatest of all the Arabian thinkers, Averrhoës, whose life extended over the greater part of the twelfth century was, in even greater degree than Avicenna, a worshipper of Aristotle.[77] While Avicenna occasionally questioned his great original, Averrhoës never did. He laid no claim to originality. To him the substance of human wisdom could never alter, being enshrined for ever in Aristotle’s pages. If Averrhoïsm differs from Aristotelianism, it does not differ consciously. Averrhoïsm is simply and solely the undiluted gospel of Aristotle, as Averrhoës conceived it.