were not known so well as they are at present. I think that it was the object of Aristotle in attributing in his Metaphysics one Intelligence to every sphere, to assume the existence of something capable of determining the peculiar course of each sphere. Later on I will show that he has not gained anything thereby; but now 1 will explain the words," according to our capacity, wisdom, and opinion," occurring in the passage which we quoted. I have not noticed that any of the commentators explain them. The term" our opinion" refers to the principle that everything is the result of natural laws, or to the theory of the Eternity of the Universe. By" our wisdom" he meant the knowledge of that which is clear and generally accepted, viz., that the existence of every one of these things is due to a certain cause, and not to chance. By" our capacity" he meant the insufficiency of our intellect to find the causes of all these things. He only intended to trace the causes for a few of them; and so he did. For he gives an excellent reason why the sphere of the fixed stars moves slowly, while the other spheres move with greater velocity, namely, because its motion is in a different direction [from the uppermost sphere]. He further says that the more distant a sphere is from the eighth sphere the greater is its velocity. But this rule does not hold good in all cases, as I have already explained . More forcible still is the following objection: There are spheres below the eighth that move from east to west. Of these each upper one, according to this rule, would have a greater velocity than the lower one: and the velocity of these spheres would almost equal that of the ninth sphere. But Astronomy had, in the days of Aristotle, not yet developed to the height it has reached at present.
According to our theory of the Creation, all this can easily be explained; for we say that there is a being that determines the direction and the velocity of the motion of each sphere: but we do not know the reason why the wisdom of that being gave to each sphere its peculiar property. If Aristotle had been able to state the cause of the difference in the motion of the spheres, and show that it corresponded as he thought to their relative positions, this would have been excellent, and the variety in their motions would be explained in the same way as the variety of the elements, by their relative position between the centre and the surface: but this is not the case, as I said before.
There is a phenomenon in the spheres which more clearly shows the existence of voluntary determination; it cannot be explained otherwise than by assuming that some being designed it: this phenomenon is the existence of the stars. The fact that the sphere is constantly in motion, while the stars remain stationary, indicates that the substance of the stars is different from that of the spheres. Abu-nasr has already mentioned the fact in his additions to the Physics of Aristotle. He says:" There is a difference between the stars and the spheres: for the spheres are transparent, the stars are opaque: and the cause of this is that there is a difference, however small it may be, between their substances and forms." So far Abu-nasr. But I do not say that there is a small difference, but a very great difference: because I do not infer it from the transparency of the spheres, but from their motions. I am convinced that there are three different kinds of substance, with three different forms, namely:--(1) Bodies which never move of their own accord; such are the
