Abu 'Ali al-Husayn ibn 'Abd-Allah ibn Sina, known in the West as Avicenna, was born in Bukhara, Persia, in 980. His father had come from Balkh to Bukhara to administer some royal estates. Bukhara was the tenth-century capital of the Samanids, a Persian dynasty theoretically acting on behalf of the Abbasid caliphate but actually quite independent of it. The Samanid rulers were noted for their patronage of the sciences and the arts. Avicenna's father was a member of the heterodox Ismaili sect, whose theology and religious philosophies embodied Neoplatonic ideas. As a boy Avicenna listened to his father and brother discuss the Ismaili doctrine of the mind and the soul. "I would listen to what they were saying and understand it," he writes, "but my soul would not accept it." His statement is significant not only because it seems to dissociate him from Ismailism but also because it indicates...