The period now under review was one prolific of authors on grammar, rhetoric, logic, exegesis, traditions and the various branches of philosophy; but the men who stand out most prominently as philosophers were then, and are now, considered heretics.[180] Al-Kendi, was born at Basra, on the Persian Gulf. He died about 870 A.D. He was a very scientific man, but a thorough rationalist in theology. He composed commentaries on the logic of Aristotle. In his great work on the unity of God he has strayed far away from Muslim dogmas. Al Farabi, another philosopher patronized by the 'Abbassides, seems to have denied not only the rigid and formal Islamic view of inspiration, but any objective revelation at all. He held that intuition was a true inspiration, and that all who had acquired intuitive knowledge were real prophets. This is the only revelation he admits. He received his philosophical training at Baghdad, where for a while he taught; but finally he went to Damascus, where he died 950 A.D. Ibn Sina, better known as Avicenna, a man of Persian origin, was a Philosopher of great note, but of him it is said that in spite of the concessions he made to the religious ideas of his age, he could not find favour for his opinions, which ill accord with the principles of Islam. He was born near Bukhara, in the year 980 A.D. For a while he taught medicine and philosophy in Ispahan. Ibn Badja, (Avempace) was one of the most celebrated Muslim Philosophers of Spain. He was born at Saragossa towards the end of the eleventh century. He is distinguished for having opposed the mystical tendencies of the teaching of Al-Ghazzali, and for maintaining that speculative science alone was capable of leading man to a true conception of his own proper nature. He was violently attacked by the orthodox divines who declared that all philosophical teaching was "a calamity for religion and an affliction to those who were in the good way."