Ha’emunoth Vehade’oth [philosophy]. Translated into Hebrew by Judah ibn Tibon.

Originally written in Arabic, HaEmunoth V'HaDe’oth was the first systematic treatise of religious Jewish philosophic literature. Saadiah Gaon’s purpose is two-fold: to demonstrate that the principles of Judaism are compatible with reason and to interpret these principles in a manner that their rationality be evident. The book is divided into ten sections each of which is subdivided into chapters. The first nine sections philosophically establish the ten fundamental principles of faith and the tenth is devoted to ethics. For a brief overview of Saadiah’s philosophic arguments in this work, see M. Waxman, Vol. I pp. 322-7. There is a certain irony in Sa'adiah's magnum opus being issued at the press of Menasseh ben Israel. Sa'adiah writes that the belief in reincarnation is foreign to Judaism, whereas Menasseh filled his work Nishmath Chaim with anecdotes relating to reincarnation. See Nishmath Chaim IV, chaps. 6-23, especially chap. 6 where Sa'adia's objections are dismissed.