The Book of Beliefs and Opinions

The first systematic work of Jewish philosophy, written in Judaeo-Arabic by Saadia Gaon, head of the academy of Sura in Babylonia, and completed in 933. Saadia wrote it for believers troubled by doubt, to show that the teachings of the Torah can also be established by reason. The introduction names four sources of knowledge: sense perception, reason, necessary inference and reliable tradition. Ten treatises follow. The first gives four proofs that the world was created from nothing and refutes rival theories of its origin. The second argues for God's unity and interprets the bodily language used of God in scripture. The third distinguishes commandments that reason can work out from those known only through revelation. Later treatises defend human free choice and discuss the soul, resurrection, the redemption of Israel and reward and punishment, and the last describes the best life as a balanced mix of pursuits rather than devotion to any single one.

It began medieval Jewish philosophy and is a clear example of how a religious tradition used the rational theology of kalām to defend creation, free will and revelation.