We are not here concerned with the vicissitudes of Saadia's personal life or of his literary career as opponent of the Karaite sect. Nor can we afford more than merely to state that Jewish science in the larger sense begins with Saadia. Hebrew grammar and lexicography did not exist before him. The Bible had been translated into several languages before Saadia's day, but he was the first to translate it into Arabic, and the first to write a commentary on it. But the greatest work of Saadia, that which did the most important service to the theory of Judaism, and by which he will be best remembered, is his endeavor to work out a system of doctrine which should be in harmony with the traditions of Judaism on the one hand and with the most authoritative scientific and philosophic opinion of the time on the other. Israeli, we have seen, was interested in science before Saadia. As a physician he was probably more at home in purely physical discussions than Saadia. But there is no evidence that he had the larger interest of the Gaon of Sura, namely, to construct a system of Judaism upon the basis of scientific doctrine. Possibly the example of Islam was lacking in Israeli's environment, as he does not seem to be acquainted with the theories and discussions of the Mutakallimun, and draws his information from Aristotelian and Neo-Platonic sources. Saadia was in the very midst of Arab speculation as is evident from the composition of his _chef d'œuvre_, "Emunot ve-Deot," Beliefs and Opinions.[37] The work is arranged on the Muʿtazilite model. The two main divisions in works of this character are _Unity_ and _Justice_. The first begins with some preliminary considerations on the nature and sources of knowledge. It proceeds then to prove the existence of God by showing that the world cannot have existed from eternity and must have been created in time. Creation implies a creator. This is followed by arguments showing that God is one and incorporeal. The rest is devoted to a discussion of the divine attributes with the purpose of showing that God's unity and simplicity are not affected by them. The section on unity closes with a refutation of opposing views, such as those of the dualists or Trinitarians or infidels. The section on Justice centres about the doctrine of free will. Hence psychology and ethics are treated in this part of the work. To this may be added problems of a more dogmatic nature, eschatological and otherwise. We shall see in the sequel that Saadia's masterpiece is modeled on the same plan.