Nothing was known of Al Mukammas until recently when fragments of his philosophical work were found in Judah ben Barzilai's commentary on the Sefer Yezirah.[35] The latter tells us that David Al Mukammas is said to have associated with Saadia, who learned a good deal from him, but the matter is not certain. If this account be true we have a second Jewish philosopher who preceded Saadia. His chief work is known by the title of "Twenty Chapters," fifteen of which were discovered in the original Arabic in 1898 by Abraham Harkavy of St. Petersburg.[36] Unfortunately they have not yet been published, and hence our account will have to be incomplete, based as it is on the Hebrew fragments in the Yezirah commentary above mentioned. These fragments are sufficient to show us that unlike Israeli, who shows little knowledge of the Muʿtazilite discussions, Al Mukammas is a real Muʿtazilite and moves in the path laid out by these Mohammedan rationalists. Whether this difference is due to their places of residence (Israeli having lived in Egypt and Kairuan, while Al Mukammas was in Babylon), or to their personal predilections for Neo-Platonism and the Kalam respectively, is not certain. Saadia knows the Kalam; but though coming originally from Egypt, he spent his most fruitful years in Babylonia, in the city of Sura, where he was gaon. The centres of Arabian rationalism were, as we know, the cities of Bagdad and Basra, nearer to Babylon and Mesopotamia than to Egypt or Kairuan. The first quotation in Judah ben Barzilai has reference to science and philosophy, their definition and classification. Science is the knowledge of the reality of existing things. It is divided into two parts, theoretical and practical. Theoretical science aims at knowledge for its own sake; practical seeks an end beyond knowledge, viz., the production of something. We call it then art. Thus geometry is a science in so far as one desires to know the nature and relations to each other of solid, surface, line, point, square, triangle, circle. But if his purpose is to know how to build a square or circular house, or to construct a mill, or dig a well, or measure land, he becomes an artisan. Theoretical science is three-fold. First and foremost stands theology, which investigates the unity of God and his laws and commandments. This is the highest and most important of all the sciences. Next comes logic and ethics, which help men in forming opinions and guide them in the path of understanding. The last is physics, the knowledge of created things. In the ninth and tenth chapters of his book Al Mukammas discusses the divine attributes. This was a very important problem in the Muʿtazilite schools, as we saw in the Introduction, and was treated in Muʿtazilite works in the first division, which went by the title of "Bab al Tauhid," the chapter on the unity.