In general we may say that Judah Halevi has a better knowledge of Aristotelian doctrines than any of his predecessors. Thus to take one example, which we used before (p. 138), Aristotle's famous definition of the soul is quoted by Isaac Israeli, Saadia, Joseph ibn Zaddik as well as by Judah Halevi. Israeli does not discuss the definition in detail.[204] Saadia and Ibn Zaddik show clearly that they did not understand the precise meaning of the definition. Judah Halevi is the first who understands correctly all the elements of the definition. And yet it would be decidedly mistaken to infer from this that Judah Halevi studied the Aristotelian works directly. By a fortunate discovery of S. Landauer[205] we are enabled to follow Judah Halevi's source with the certainty of eyewitnesses. The sketch which he gives of the Aristotelian psychology is taken bodily not from Aristotle's De Anima, but from a youthful work of Ibn Sina. Judah Halevi did not even take the trouble to present the subject in his own words. He simply took his model and abridged it, by throwing out all argumentative, illustrative and amplificatory material. Apart from this abridgment he follows his authority almost word for word, not to speak of reproducing the ideas in the original form and order. This is a typical and extremely instructive instance; and it shows how careful we must be before we decide that a mediæval writer read a certain author with whose ideas he is familiar and whom he quotes. In the sketch of philosophical theory Judah Halevi first speaks of the hyle (ὕλη) or formless matter, which according to the philosophers was in the beginning of things contained within the lunar sphere. The "water" in the second verse of Genesis ("and the spirit of God moved upon the face of the water") is supposed by them to denote this primitive matter, as the "darkness" in the same verse and the "chaos" ("Tohu") in the first verse signify the absence of form and composition in the matter (the Aristotelian στέρησις). God then willed the revolution of the outermost sphere, known as the diurnal sphere, which caused all the other spheres to revolve with it, thereby producing changes in the hyle in accordance with the motions of the sphere. The first change was the heating of that which was next to the lunar sphere and making it into pure fire, known among the philosophers as "natural fire," a pure, fine and light substance, without color or burning quality. This became the sphere of fire. The part that was further away changed as a result of the same revolution into the sphere of air, then came the sphere of water, and finally the terrestrial globe in the centre, heavy and thick by reason of its distance from the place of motion. From these four elements come the physical objects by composition. The forms (in the Aristotelian sense) of things are imposed upon their matters by a divine power, the "Intellect, and Giver of Forms"; whereas the matters come from the hyle, and the accidental