Rashi was the outstanding Biblical commentator of the Middle Ages. He was born in Troyes, France, and lived from 1040 to 1105, surviving the massacres of the First Crusade through Europe. He was a fantastic scholar and studied with the greatest student of Rabbenu Gershom of Mainz At twenty-five, he founded his own academy in France. Rashi's commentary on the Bible was unique. His concern was for every word in the text which need elaboration or explanation. Moreover, he used the fewest words possible in his commentaries. Most of his explanations were not written by him. Apparently, students would ask him questions about the text, or he would rhetorically ask questions about specific words, and a student would write his short, lucid answers in the margin of the parchment text. These answers comprise Rashi's commentary. We now have the answers, but the trick to studying Rashi is to figure out what the problem was with the text or the grammar of a given word. Besides explaining individual words, Rashi also made use of the the great oceans of midrash. However, instead of just quoting the early rabbis, Rashi applied the stories specifically to the Bible text; often abridging them. He assumed that his students knew the midrash; he just emphasized its immediate relevance to the TaNaCH. Rashi is also important for students of French. Many words in the Bible were unknown to Rashi's students, and obviously there would ask what a particular word meant and Rashi would give the answer in Old French using Hebrew transliteration. These transliterations provide important insights into the development of French and its pronunciation. The original printed Bible text by Daniel Bomberg in 1517 included Rashi's commentary. That commentary became so popular that there are now more than 200 commentaries on his commentary. It is assumed in traditional circles that when you read the TaNaCh, you also read Rashi. Rashi's commentary on the Talmud was even more important than his TaNaCh commentary. The Talmud was written in legalese: terse, unexplained language with no punctuation. Rashi provided a simple explanation of all Gemarra discussions. He explained all of the terse phrases; he explained the principles and concepts assumed by the sages who put together the Gemarra. His simple, brief explanations for practically every phrase of the Gemara made the Talmud understandable to the non-scholar. It became an instant best seller, and, to this day, it is unthinkable to study Talmud without studying Rashi's commentary at the same time.

ISAAC BEN JUDAH OF MAINZ (11th century), German scholar; teacher of Rashi. Practically no biographical details are known of him or his family. R. Isaac was head of the famous yeshivah in Mainz founded by his teacher R. Gershom b. Judah, to whom he was apparently related, as he was to Rashi. He seems to have come from France (Zedekiah b. Abraham ha-Rofe, Shibbolei ha-Leket ed. by Buber (1886). 66 no. 93). He was also a pupil of Eliezer ha-Gadol of Metz who was also one of the heads of Mainz yeshivah. In addition to Rashi, he numbered Eliakim b. Meshullam among his distinguished pupils. Eliakim refers to him as Moreh Zedek ("the righteous teacher") whenever he mentions him in his commentary to Yoma and Rashi uses the same title on Yoma 16b and in his responsa. According to Abraham Epstein, the commentary attributed to Rabbenu Gershom in the Romm (Vilna) editions of the Talmud to the tractates Menahot, Bekhorot, Arakhin, Temurah, Keritot, Me'ilah, Tamid, Hullin, Ta'anit, and Bava Batra was compiled in Isaac's bet midrash. Eight of his responsa are included in the Teshuvot Hakhmei Zarefat ve-Loter (1881), and in the introduction to this work J. Mueller gives a list of 17 of his responsa and novellae which are scattered throughout the literature. I. Elfenbein's edition of Rashi's responsa (1943) contains 38 of Isaac's, mainly directed to Rashi.

KASHER, MENAHEM (1895–1983), rabbi and halakhist, distinguished for his research in talmudic and rabbinic literature. Kasher, born in Warsaw, studied under the greatest Polish rabbis of his time, and was primarily influenced in his method of study by Abraham Bornstein. He was ordained by Meir Dan Plotzki in 1915 and went to Erez Israel in 1925 as an emissary of Abraham Mordecai Alter, the head of the hasidic Gur dynasty, on whose behalf he founded in Jerusalem the yeshivah Sefat Emet, which he directed and managed for two years. Despite his communal work and his religious activity, Kasher never held any official appointment, and his reputation derives mainly from his literary work. This consists for the most part of varied anthologies, encyclopedic in character, which he not only initiated and wrote, but also took the responsibility for financing. His Torah Shelemah is an encyclopedia of the Talmud and Midrash, in which all relevant material in the oral law, both published and in manuscript, is collected according to the Scriptural verse to which it applies together with notes, expositions, and supplements. Thirty-three volumes, covering Genesis–Leviticus 24:23 had been published by 1981 (the first volume appeared in 1927). For this work, Kasher was awarded the Israel Prize in 1962. Gemara Shelemah (1960) deals with the first nine pages of the tractate Pesahim, with variant readings from all the known manuscripts and with all the relevant comments of the rishonim, together with notes and expositions by Barukh Naeh edited by Kasher—the beginning of a long-term project toward a scientific edition of the entire Talmud. Haggadah Shelemah (1956) comprises the Passover Haggadah with variant readings, notes, and expositions, to which are added a selection of relevant homiletic comments. Sarei ha-Elef (1959) consists of a list of Hebrew books whose authors lived between 500 and 1500, edited and arranged in conjunction with J. Mandelbaum. These compilations are basic reference works for all research in talmudic and rabbinic literature. In 1950 Kasher founded, in Jerusalem and in New York, the Torah Shelemah Institute for research and publication.

In 1956 Kasher discovered an extensive collection of writings by Joseph Rozin, author of Zafenat Pa'ne'ah. In order to edit and publish this material he founded, together with the Yeshiva University in New York, the Zafenat Pa'ne'ah Institute, which by 1970 had issued 12 volumes. Aside from these projects, Kasher published many works on varied subjects. Mefa'ne'ah Zefunot (1959), elucidating the halakhic terms and concepts used by Rozin in the above-mentioned book; Sefer ha-Rambam ve-ha-Mekhilta de-Rabbi Shimon b. Yohai (1943), clarifications of the sources of Maimonides; Shabbat Bereshit ve-Shabbat Sinai, in Talpiyoth, 1 (1944), and Ha-Shabbat u-Mizrah ha-Olam, in Ha-Pardes, 28 (1954), elucidations of the problem of the International Date Line prompted by the dilemma of the Jewish war refugees in Japan; a small collection of responsa by Rashi (1925); Targum Yerushalmi ha-Shalem from a Rome manuscript, and others. Kasher also devoted himself to the clarification of contemporary halakhic problems, and to comparisons of the view of the sages with modern concepts. These appear mostly in the annual publication No'am (1958– ) which Kasher founded and which he edited. The halakhic aspects of such problems as artificial insemination, autopsies, are dealt with in this publication. Kasher also wrote an extensive article to prove the antiquity of the Zohar, and published many articles on the importance of manuscripts for a complete and correct understanding of the Talmud. He instituted an eruv for Manhattan in New York which gave rise to considerable controversy. In 1968 there appeared his Ha-Tekufah ha-Gedolah in which he maintained that the establishment of the State of Israel is the beginning of the Redemption foretold by the prophets, and its development its progressive realization. A hitherto unknown work on a similar theme by R. Hillel Shklover, a disciple of Elijah Gaon of Vilna, is appended to the work with a commentary by Kasher.