רלב"ג

Rav Levi ben Gershom (5048/1288–6 Iyar 5104/1344), the Ralbag, known in Latin sources as Gersonides, was a rishon of Provence — parshan of the Tanach, baal machshavah, and one of the great mathematicians and astronomers of his age. He was born in Bagnols in Languedoc, southern France, to a family known for piety and depth in Talmud — some say his father was Rav Gershon ben Shlomo — and he lived in Avignon and Orange without ever holding rabbinic office.

His peirush on Tanach covers the Torah, Neviim Rishonim, Mishlei, Iyov, Kohelet, Shir HaShirim, Rut, Esther, Daniel, Ezra-Nechemiah, and Divrei HaYamim, each parshah opened in three parts: the meaning of the words, the run of the parshah, and the “to’aliyot” — lessons drawn out in deiot, middot, and mitzvot; in Shemot and Vayikra he adds the “shorashim,” the halachic roots of each mitzvah learned from the diyuk of the pesukim. The peirush on the Torah was among the very first Hebrew sefarim printed (Mantua, 5236/1476), and his peirushim on Neviim Rishonim and on Iyov entered the Mikraot Gedolot of the early Venice printings and stand in the standard editions since. In halachah he left Shaarei Tzedek on the thirteen middot of Rabbi Yishmael — the only one of his Talmudic works extant, printed in Livorno in 5560/1800 — besides a peirush on Berachot, Mechokek Safun on the aggadot of the fifth perek of Bava Batra, and two teshuvot, which have not survived.

His great work of machshavah, Milchamot Hashem, was twelve years in the writing and completed in 5088/1328: six chalakim on hisharut hanefesh, dreams and nevuah, the knowledge of Hashem, hashgachah, the heavenly bodies, and chiddush haolam — where he holds firmly that the world was created. Some of his positions drew sharp hasagot from chachmei hadorot, the Rivash and the Abarbanel among them, yet his peirush on Tanach was received everywhere and is cited in sifrei halachah and machshavah to this day.

In 5081/1321 he wrote Maaseh Choshev on arithmetic and the ways of counting combinations, with early proofs by mathematical induction; he proved the sine law and computed tables of sines; and he invented the measuring instrument called the mateh Yaakov, with which seafarers measured the heavens for some four hundred years. He built his astronomy on his own observations of eclipses rather than on Ptolemy’s model, which he showed could not stand against what the eye measures, and the astronomical part of Milchamot Hashem was translated into Latin in his lifetime. He was niftar on 6 Iyar 5104/1344, and by tradition was buried in Metz. A crater of the moon bears the name “Rabbi Levi” in his honor, and it is told that the Vilna Gaon said: “Would that I might sit in the mechitzah of the Ralbag in Gan Eden.”