Skip to main content

Isaac ben Mordecai


ISAAC BEN MORDECAI (known as Ribam, initials of R abbi I saac B en M ordecai; 12th century), German tosafist. Isaac was also known as Isaac b. Mordecai of Bohemia and Isaac b. Mordecai of Prague. The abbreviated form of his name, Ribam, led to his being confused at times with *Isaac b. Meir (see Urbach, Tosafot, 170 no. 37). Active in the community of Regensburg, he served as head of its bet din and was regarded as the greatest scholar of the town and its leader (as described by Jacob b. Meir *Tam in Sefer ha-Yashar, part of responsa ed. by F. Rosenthal (1898), 178 no. 80). He was a pupil of *Isaac b. Asher ha-Levi (Riba i) of Speyer and of Jacob Tam. He compiled tosafot to most tractates of the Talmud, a large part of them while with his teachers. A considerable part of his tosafot to Bava Batra are included in the printed edition of the Talmud and in the tosafot of *Isaiah di Trani. He is known to have written tosafot to the tractates Pesaḥim, Mo'ed Katan, and Bava Kamma compiled before his teacher, Isaac, and to Shabbat, Ketubbot, Gittin, Sotah, Nazir, and Bava Meẓia. He is quoted in the printed tosafot to Yoma, Ḥagigah, Sanhedrin, Zevaḥim, and Ḥullin, and in Sefer ha-Ravyah and Or Zaru'a. *Eliezer b. Nathan of Mainz sent his book to him and his colleagues *Ephraim b. Isaac and Moses b. Joel on the bet din of Regensburg. They criticized many of his statements and in his reply Eliezer treated them with great respect. He also sent them the well-known responsum on ḥallonot ("windows," i.e., the prohibition against disturbing the privacy of a neighbor by opening a window facing his premises).


Eliezer b. Nathan, Sefer Rabban, ed. by S. Albeck (1904), introd. p. xi; V. Aptowitzer, Mavo le-Sefer Ravyah (1938), 29, 42f., 288, 378f.; Epstein, in: Tarbiz, 12 (1940/41), 200–2; Urbach, Tosafot, 167–70.

[Shlomoh Zalman Havlin]

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Isaac ben Mordecai." Encyclopaedia Judaica. . 25 Jun. 2019 <>.

"Isaac ben Mordecai." Encyclopaedia Judaica. . (June 25, 2019).

"Isaac ben Mordecai." Encyclopaedia Judaica. . Retrieved June 25, 2019 from

Learn more about citation styles

Citation styles gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, cannot guarantee each citation it generates. Therefore, it’s best to use citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.