יצחק בן יהודה

Rav Yitzchak ben Yehuda (born c. 4770/1010), known in English sources as Isaac ben Judah of Mainz, was rosh yeshiva of Magentza (Mainz) in the eleventh century and one of the rebbeim of Rashi. In his youth he learned from his relative Rabbeinu Gershom Meor HaGolah, and from Rav Eliezer HaGadol ben Yitzchak; some sources bring that he learned as well from Rav Hai Gaon in Rome. When Rav Yaakov ben Yakar was niftar in 4824/1064, he took up the headship of the yeshiva. Questions reached him from as far as Bohemia and northern France, and those who asked addressed him with titles such as Rabbeinu HaKadosh. Several sources point to a family connection between him and Rashi.

Rashi learned in his yeshiva for a relatively short period and was shaped by him less than by his other rebbeim, yet he quotes him many times and corresponded with him in halacha, calling him mori tzedek and Rabbeinu HaRav HaGadol — while also differing with him, and on one occasion Rav Yitzchak withdrew his own view in the face of Rashi’s words. Rashi corrected portions of his Gemara text against Rav Yitzchak’s copy, whose girsaot were held to be exact in later generations too. Among his other talmidim were Rav Elyakim ben Meshullam HaLevi; Rav Yitzchak ben Asher HaLevi, the Riva, first of the Baalei HaTosafot in Ashkenaz; and the Bnei Machir, authors of Maaseh HaMachiri, which brings a great many of his practices.

He stood among the foremost respondents of Ashkenaz in his century. Some sixty-five teshuvot are attributed to him with certainty, most of them written to Rashi and to the Bnei Machir; further responsa of his lie scattered through the Pardes HaGadol, Likutei Pardes, the Or Zarua, the Shibbolei HaLeket, the Mordechai and the teshuvot of the Maharam of Rothenburg. There is clear evidence that commentaries on most of Shas were written in his beit midrash, and his commentary lay before Rashi, who used it in a number of places.

In psak he was careful and stringent — in the matter of yayin nesech, and in baking bread together with meat or cheese in one oven — writing that it is a mitzvah to be stringent and to set a fence around the matter. He gave great weight to minhag: it is a mitzvah, he wrote, to uphold the practice of the rishonim as far as a man is able, and minhag uproots halacha. He held that obedience to the enactments of the kehillah carries force from the Torah, and he raised the standing of the Talmud Bavli in Ashkenaz over the Yerushalmi, giving a central place to the teshuvot of the Geonim of Bavel. His son Rav Yehuda was among the chachamim of the Mainz yeshiva, and the chachamim of Mainz relied on him to recover his father’s practices; he was killed together with his wife Yehudit and their son Yitzchak in the gezeirot of tatnu.