middle ages. We have already seen in the Introduction (p. xxxiv) that Aristotle conceived the world as a series of concentric spheres with the earth in the centre. The principal spheres are eight in number, and they carry in order, beginning with the external sphere, (1) the fixed stars, (2) Saturn, (3) Jupiter, (4) Mars, (5) Mercury, (6) Venus, (7) Sun, (8) Moon. To account for the various motions of the sun and the planets additional spheres had to be introduced amounting in all to fifty-six. But the principal spheres remained those mentioned. Each sphere or group of spheres with the star it carries is moved by an incorporeal mover, a spirit or Intelligence, and over them all is the first unmoved mover, God. He sets in motion the outer sphere of the fixed stars, and so the whole world moves. There is nothing said in this of the origin of these spheres and their intelligible movers. On the other hand, in the Neo-Platonic system of Plotinus all existence and particularly that of the intelligible or spiritual world issues or emanates from the One or the Good. Intellect is the first emanation, Soul the second, Nature the third and Matter the last.
On account of the confusion which arose in the middle ages, as a result of which Neo-Platonic writings and doctrines were attributed to Aristotle, Alfarabi and Avicenna worked out a scheme which combined the motion theory of Aristotle with the doctrine of emanation of Plotinus. The theory is based upon a principle alleged to be Aristotle's that from a unitary cause nothing but a unitary effect can follow. Hence, said Avicenna, God cannot have produced directly all the world we see in its complexity. He is the direct cause of the first Intelligence only, or first angel as Judah Halevi calls him. This Intelligence contemplates itself and it contemplates its cause. The effect of the latter act is the emanation of a second intelligence or angel; the effect of the former is a sphere—that of the fixed stars, of which the first Intelligence is the mover. The second Intelligence again produces a third Intelligence by its contemplation of the First Cause, and by its self-contemplation it creates the second sphere, the sphere of Saturn, which is moved by it. So the process continues until we reach the sphere of the moon, which is the last of the celestial spheres, and the Active Intellect, the last of the Intelligences, having in charge the sublunar world.
This fanciful and purely mythological scheme arouses the antago-
