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Isaac ben Solomon Israeli (ca. 855–ca. 955) was an accomplished physician and one of the earliest medieval Jewish philosophers. Although dismissed by Maimonides as “merely a physician” whose books were “futile and vain,” he introduced Neoplatonism into Jewish thought and by so doing had an influence on later developments in Jewish philosophy,Born in Egypt, Israeli relocated to Qayrawan, where he was court physician to the Aghlabid amir and the Fatimid caliph. His books, intended by the childless Israeli as a guarantor of his immortality, include both medical treatises (on such su…

Judah ben Elijah Hadassi ha-Avel (“the Mourner,” fl. 1148–1149) was the outstanding Karaite of twelfth-century Byzantium. Although he lived in a Christian country and very likely did not know Arabic, his major opus, Sefer Eshkol ha-Kofer (The Cluster of Henna, Song of Songs 1:14) serves as a summa of Karaite Judaism as it had developed under Islam from the proto-Karaite ʿAnan ben David to the demise of the Jerusalem Karaite community in 1099. It provides an overview of Karaite law, polemics, theology, heresiology, and much more. …

It is unclear how the biblical calendar was set, despite the fact that the observance of many biblical laws, such as the holiday celebrations, is dependent upon calendrical calculation. In the immediate postbiblical period, at the end of the Second Temple, there were competing calendrical systems, and it is unclear which one was predominant. The best-known of these calendars was the Pharisaic luni-solar system, which eventually became the accepted rabbinic calendar. The months of this calendar were lunar, beginning with the new moon. The years, however, f…

Neither the authors of the Bible nor the rabbis of the talmudic era expressed their ideas in philosophical terms. The Bible assumes the existence of a creative, providential God, without attempting to demonstrate His existence. Major theological questions, such as the existence of evil or God’s foreknowledge and human free will, find multiple, and often contradictory, solutions in the different books of the Bible. Rabbinic literature picks up the theological concerns of the Bible, but there are …

Judah ben Joseph ben Isaac ibn Simeon was the student for whom Moses Maimonides ostensibly wrote his Guide of the Perplexed (and not Judah ben Joseph ibn ʿAqnīn as was once thought). Born in Ceuta, Morocco, in the mid-twelfth century, Ibn Simeon went to Alexandria and, after corresponding with Maimonides, arrived in Fustatto study with the Master sometime between 1182 and 1184. Maimonides praised his student’s poetry and his presumed ability to grasp metaphysics through diligent study.Ibn Simeon eventually left Egypt on business but continued to correspond with Maimonid…

David (Dāwūd) ibn Marwān al-Muqammiṣ (perhaps al-Muqammaṣ) was active in mid-ninth-century Syria and northern Iraq, and was the first medieval Jewish philosopher to leave identifiable writings. He is said to have converted to Christianity, studied many years with Nonnus of Nisibis, and then returned to Judaism; his writings demonstrate a great deal of Christian influence. Both Karaites and Rabbanites claim him as one of their own, but the evidence is not sufficient to make a definite identification. Very little is otherwise known about him.Al-Muqammiṣ wrote Arabic treatises on…

Karaism (Heb. qaraʾut), the form of Judaism which claims to adhere to a more literal interpretation of the Bible ( miqraʾ) than that of the Rabbanites, the exponents of Rabbinic Judaism, and which rejects the institution of Jewish Oral Law as codified in the Mishna and Talmud, had its origins and greatest intellectual accomplishments in the Islamic world. It emerged in Iran, Iraq, and the Land of Israel in the late eighth and ninth centuries, and it had a Golden Age in tenth- and eleventh-century Jerusalem. During …