The Book of Substances

Isaac ben Solomon al-Isrā’īlī, a physician and philosopher, was born in Egypt but spent most of his career in Qayrawān, Tunisia, where he was court physician for both the Aghlabids and the Fātimids. An early Jewish Neoplatonist, al-Isrā’īlī wrote several philosophical works. He held that the universe existed through a process of divine emanation, although unlike some Neoplatonists, he allowed that the divine will played a role in it. His primary student in philosophy was Dunash Ibn Tamīm (ca. 890–ca. 956), and he also corresponded with Se‘adya Ga’on (882–942) on philosophical matters. Al-Isrā’īlī was an accomplished medical author; his extant works include monographs on uroscopy, dietary regimens, and fevers. Some of his works were translated into Latin and other languages, and two became part of the medieval Latin medical curriculum. He never married and was childless, reportedly quipping that his book would survive better than any children.