Like Israeli Saadia shows considerable familiarity with Aristotelian notions as found in the Logic, the Physics and the Psychology. It is doubtful, however, whether he really knew Aristotle's more important treatises at first hand and in detail. The "Categories," a small treatise forming the first book of Aristotle's logic, he no doubt knew, but the other Aristotelian concepts he probably derived from secondary sources. For while he passes in review all the ten categories showing that none of them is applicable to God,[42] we scarcely find any mention of such important and fundamental Aristotelian conceptions as matter and form, potentiality and actuality, the four causes, formal, material, efficient and final--concepts which as soon as Aristotle began to be studied by Al Farabi and Avicenna became familiar to all who wrote anything at all bearing on philosophy, theology, or Biblical exegesis. Nay, the very concepts which he does employ seem to indicate in the way he uses them that he was not familiar with the context in which they are found in the Aristotelian treatises, or with the relation they bear to other views of Aristotle. Thus no one who knew Aristotle at first hand could make the mistake of regarding his definition of the soul as making the latter an accident.[43] When Saadia speaks of six kinds of motion [44] instead of _three_, he shows clearly that his knowledge of the Aristotelian theory of motion was limited to the little of it that is contained in the "Categories." We are thus justified in saying, that Saadia's sources are Jewish literature and tradition, the works of the Mutakallimun, particularly the Muʿtazilites, and Aristotle, whose book on the "Categories" he knew at first hand. Saadia tells us he was induced to write his book because he found that the beliefs and opinions of men were in an unsatisfactory state. While there are some persons who are fortunate enough to possess the truth and to know that they have it and rejoice thereat, this is not true of all. For there are others who when they have the truth know it not, and hence let it slip; others are still less fortunate and adopt false and erroneous opinions, which they regard as true; while still others vacillate continually, going from one opinion and belief to another. This gave him pain and he thought it his duty to make use of his limited knowledge to help them. A conscientious study of his book will tend to remove doubt and will substitute belief through knowledge for belief through tradition. Another result of such study, not less important, will be improvement of character and disposition, which will affect for the better a man's life in every respect, in relation to God as well as to his fellowmen.[45]