צבי הירש קיידנובר

Rav Tzvi Hirsch Kaidanover (c. 5410/1650–15 Adar II 5472/1712) is known to all generations by his sefer: the Kav HaYashar, one of the most beloved and widely printed mussar works in the Jewish library. He was the son of Rav Aharon Shmuel Kaidanover, the Maharshak, and his childhood was shaped by the family’s flight through the gezeirot of tach v’tat, in which two of his sisters were murdered; the family wandered with his father’s rabbanut through Nikolsburg, Glogau and Fuerth. His rebbe muvhak in the hidden derech was Rav Yosef Yoska, rav of Minsk and later Dubno, author of the Yesod Yosef, whose kabbalah-founded mussar left the deepest mark on him; in halacha he followed his father.

Returning to Vilna, he prospered in trade and stood among the community’s notables — until a false denunciation cast him and his son into prison in chains. On his release he left Lita for Frankfurt, and turned his trials into Torah: he brought his father’s sefarim to print, adding his own introductions, and there wrote the Kav HaYashar, first printed in Frankfurt in 5466/1706.

The sefer — mussar and yirat Shamayim built on the kabbalah of his rebbe’s Yesod Yosef, told through stories and practical guidance — is woven from his own name: Kav in gematria is 102, the number of its chapters and the value of “Tzvi,” and HaYashar is an anagram of “Hirsch.” He himself prepared its Yiddish rendering, printed beside the Hebrew, and it has since appeared in hundreds of editions and remains a staple of batei Yisrael to this day. His son-in-law, Rav Elchanan Henle Kirchhahn, wrote the mussar sefer Simchas HaNefesh in its spirit. Rav Tzvi Hirsch was niftar in Frankfurt on 15 Adar II 5472 and rests there.