Kav ha-Yashar , authored by Tzvi Hirsch Kaidanover, a rabbi at Frankfurt and son of Aaron Samuel Kaidanover, is an "ethical-kabbalistic collection of stories, moral guidance, and customs", and one of the most popular works of musar literature. It serves as a guide to "God-fearing piety and to preserving the norms of the community", framing its teachings in the context of "individual providence and the reckoning of sins and merits". The title of the work alludes to the number of chapters it contains, as well as the author's middle name.