Aristotle was the first to delimit the boundaries of the various branches of philosophy and to treat them systematically. Logic, physics, psychology, biology, metaphysics, ethics, politics, rhet oric and poetics are all rigidly distinguished, and each of them has a treatise or treatises devoted to it in the extant works of Aristotle. The politics and the poetics were rather neglected by the Jews, the former because the Jews had no State of their own and the latter because it had no bearing on theology or the Bible. To be sure there is poetry in the Bible, but the Jewish philosophers were interested in doctrine and not in literary form. All the other works of Aristotle, notably the logic, physics, psy chology, metaphysics and ethics, were carefully studied, even if not at first hand, and the ideas contained therein were laid under contribution in the attempt to establish a scientific Jewish phi losophy. Interest in Aristotle's problems was taken partly for their own sake, for the Jews did develop a scientific temper, and partly for an apologetic purpose to defend the dogmas of Ju daism scientifically. And Biblical exegesis was introduced as an aid in the apologetic activity.
The most important part of the Aristotelian philosophy for the Jewish theologians was naturally his idea of God. His was the first scientific attempt to prove the existence of God irrespective of the religious motive. As is well known, Aristotle proves that the motion at the basis of all natural phenomena in the heavens and on earth requires for its existence an immovable mover, and an analysis of the concept of an immovable mover leads to the recognition of a being having the Divine attributes of unity and incorporeality. This demonstration was of immense importance for a religious philosophy and was adopted eagerly by the Jewish philosophers as soon as it became known to them. It took the place immediately of the Kalamistic proofs of the earlier writers and prepared the downfall of that system of doctrine. For Aris totle's proof of the existence of God could not be taken as an isolated bit of argumentation. Aristotle's ideas are not episodic, they are above all systematic. The argument for the existence of God carries with it the entire physical and metaphysical sys tem of Aristotle without which it has no meaning. Hence Mai monides, in the second book of the Guide of the Perplexed, pref aces the Aristotelian proof with a list of 25 propositions, which sum up in the form of dogmatic conclusions the physical and metaphysical theories of Aristotle. Abraham Ibn Daud, in his Exalted Faith, does the same thing in a less concentrated and less skilful form. And Hasdai Crescas (1340-1410), the Anti rationalist, undermines the Aristotelian doctrine by undertaking to refute, in his Light of the Lord, the 25 principles laid down by Maimonides.
The difference in method between the Kalamistic proofs of the existence of God and the Aristotelian is that the former were all based upon the doctrine of the creation of the world in time. Creation was proved first and the existence of God followed from creation. The Aristotelian proof was direct, though in prov ing God's incorporeality the assumption is that the world is eternal. This meant, of course, that one had to exercise caution in availing oneself of the Aristotelian arsenal for the purpose of borrowing arms for the defence of Judaism. There were those —not at all insignificant persons—who made precisely this charge that, in following the teachings of Aristotle, Maimonides and his school were falsifying Judaism. Maimonides did make use of the Aristotelian proof in place of the Kalamistic because he did not believe the creation of the world in time to be demonstrable by reason. But neither did he believe that Aristotle had suc ceeded in proving the world's eternity. As a matter of pure logic he thinks that the balance of probability is in favor of creation, and in creation he believes.
The treatment of the Divine attributes in the philosophy of the Jewish Aristotelians is also based on Aristotelian ideas. Unity and incorporeality are derived in Aristotelian fashion from the concept of the "unmoved mover." Thus the Aristotelian con ceptions of matter and form and .motion and change and nature and potentiality and actuality are adopted and laid under con tribution. Nevertheless the doctrine of Divine attributes in its details is not wholly Aristotelian. In the first place God is the Creator ex nihilo in accordance with the traditional interpreta tion of the creation story in Genesis and not merely the prime mover causing the combination of the eternal matter with the eternal forms as in Aristotle. Secondly, there is an element of neo-Platonic transcendence in the conception of God both in the philosophy of Maimonides and in that of the other Jewish Aris totelians, who differ only in the degree of transcendence they ascribe to God, Maimonides being extreme in his views on the subject, while Gersonides is more moderate.
The Aristotelian cosmology as it relates to the motions of the heavenly bodies and their several spiritual movers—the spirits of the spheres, as they were called, or the separate Intelligences— was also adopted in part and made use of to find a place for the Biblical doctrine of angels. The angels of which the Bible speaks are none other than the movers of the spheres, and they are immaterial beings.