of gaon, “excellence”) attempted to standardize Jewish law, custom, and liturgy in accordance with their own practices, which they set forth in their replies (responsa) to inquiries from Diaspora communities. Thus, the hegemony over Jewry passed from Palestine to Babylonia, and the Babylonian Talmud came to be the most authoritative rabbinic document.
In the cultural ambit of Islam, rabbinic Judaism encountered Greek philosophy as recovered and interpreted by Islamic commentators. Rabbinic intellectuals began to cultivate philosophy to defend Judaism against the polemics of Islamic theologians and to demonstrate to other Jews the rationality of their revealed faith and law. Medieval Jewish philosophy typically concerns the attributes of God, miracles, prophecy (revelation), and the rationality of the commandments. The most notable philosophical interpretations of Judaism were put forth by the 9th-century Babylonian gaon Saadia ben Joseph, by Judah Ha-Levi in the 12th century, and, preeminently, by Moses ben Maimon (Maimonides) in the 12th century (Guide for the Perplexed, c. 1190; trans. 1919). The exposure to systematic logic also affected rabbinic legal studies in the Muslim world and is evident in numerous posttalmudic codifications of Jewish law, the most famous being Maimonides' elegant Mishneh Torah.
Medieval Judaism developed two distinctive cultures, Sephardic (centered in Moorish Spain) and Ashkenazic (in the lands of the Holy Roman Empire. Philosophy and systematic legal codification were distinctly Sephardic activities and were opposed by the Ashkenazim, who preferred intensive study of the Babylonian Talmud. The great Rhineland school of Talmud commentary began with the 11th-century scholar Solomon ben Isaac (Rashi) of Troyes and continued with his grandsons and students, known as the tosaphists, who produced the literature of tosaphoth (“additions” to Rashi's Talmud commentary).
Throughout the medieval period, Judaism was continually revitalized by mystical and ethical-pietistic movements. The most significant of these were the 12th-century German Hasidic, or “pietist,” movement and the 13th-century Spanish Cabala, of which the most influential work was Sefer ha-zohar (The Book of Splendor) by Moses de León.
The Cabala is an esoteric theosophy, containing elements of Gnosticism and Neoplatonism, that describes the dynamic nature of the godhead and offers a powerful symbolic interpretation of the Torah and the commandments. It began in small, elite scholarly circles but became a major popular movement after the calamitous expulsion of the Jews from Catholic Spain in 1492.