Sefer Ha-Yashar (The Book of Righteousness); one of the most popular ethical books in the Middle Ages. It was frequently attributed to R. Tam, the tosafist, who wrote a book by a similar name. Some manuscripts attribute the book to Zerahiah ha-Yevani, but there is no evidence for this. Others have suggested R. Jonah Gerondi as the author but his ideas are contradicted by Sefer Ha-Yashar. It remains an anonymous work probably written in the 13th century. The style and language conform to contemporaneous philosophical ethical writings and ideas; the author especially made use of Aristotelian terms and concepts. He includes a number of other beliefs which hint at possible qabbalistic tendencies. The work is also similar is substance to ideas present amongst Ḥasidei Ashkenaz.