[“The Book of the Righteous” - ethics]. Anonymous.

Sepher HaYashar, probably written in the 13th century, was one of the most popular ethical works of the Middle Ages. It is often ascribed to the Tosaphist Jacob (Rabbeinu) Tam, as he authored an Halachic work under the same title. The style and language conform to the contemporary philosophies of the time with references to Aristotelian terms and concepts, yet some of the main ideas conflict with conventional philosophy to the extent that some scholars attributed the authorship to a kabbalist not wishing to reveal the full scope of his mystical beliefs. Others find similarities between the work and the ethical concepts of the Aschkenazic Hasidic (pietist) movement which peaked in the 13th century. As of yet, no critical edition of this work has been published and until the correct text is ascertained, the questions regarding it's authorship and underlying philosophical thought are still in doubt. For a brief survey of the structure and contents of Sepher HaYashar, see M. Waxman, Literature, Vol. II, pp. 276-8.