purpose of avoiding something, and never obtained that object, the motion would be in vain. The circular motion of the sphere is consequently due to the action of some idea which produces this particular kind of motion; but as ideas are only possible in intellectual beings, the heavenly sphere is an intellectual being. But even a being that is endowed with the faculty of forming an idea, and possesses a soul with the faculty of moving, does not change its place on each occasion that it forms an idea; for an idea alone does not produce motion, as has been explained in [Aristotle’s] Metaphysics. We can easily understand this, when we consider how often we form ideas of certain things, yet do not move towards them, though we are able to do so; it is only when a desire arises for the thing imagined, that we move in order to obtain it. We have thus shown that both the soul, the principle of motion, and the intellect, the source of the ideas, would not produce motion without the existence of a desire for the object of which an idea has been formed. It follows that the heavenly sphere must have a desire for the ideal which it has comprehended, and that ideal, for which it has a desire, is God, exalted be His name! When we say that God moves the spheres, we mean it in the following sense: the spheres have a desire to become similar to the ideal comprehended by them. This ideal, however, is simple in the strictest sense of the word, and not subject to any change or alteration, but constant in producing everything good, whilst the spheres are corporeal; the latter can therefore not be like this ideal in any other way, except in the production of circular motion; for this is the only action of corporeal beings that can be perpetual; it is the most simple motion of a body; there is no change in the essence of the sphere, nor in the beneficial results of its motion.