The four elements which comprise matter in the sublunary sphere follow rectilinear motion, which follows from a “natural property”; on the other hand, the ‘fifth element’ which makes up the heavenly spheres follows perfect circular motion, and this is due to a “soul”. Maimonides is at pains to explain that those who dispute the assertion that the heavenly spheres are endowed with souls

wrongly assume that when we ascribe a soul to the heavenly spheres we mean something like the soul of man, or that of an ass, or ox. We merely intend to say that the locomotion of the sphere undoubtedly leads us to assume some inherent principle by which it moves; and this principle is certainly a soul.

Maimonides explains further that animate beings move “either by instinct or by reason”; under ‘instinct’ he files all motion which is in response to the fulfillment of needs or the avoidance of harm; since the heavens move continuously and keep arriving at the same point over and over again, their motion must be due to reason and not instinct.

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

That idea is God; thus, the motion of the spheres is essentially the motion of an intellectual being which seeks to achieve ‘closeness’ to God by way of its circular motion (see, for example, Ibn Tufail) — perfect, ceaseless, circular, constant — and it is in this sense that God ‘moves’ the spheres; he is the ideal which is comprehended by the soul which animates the spheres.

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, … 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

Although the heavenly spheres themselves are corporeal beings, with a material existence, they are each associated with an Intelligence; these are

purely spiritual beings, which do not reside in corporeal objects, and which derive existence from God (كلها فائضة عن الله تعالى); and these form the intermediate element between God and this material world (هي الوسائط بين الله و بين هذه الأجسام كلها).

When Scripture speaks of the heavens praising and glorifying God — the example he gives is Psalms XIX 2: “The heavens declare the glory of God” — Maimonides asserts that “it is a great error to think that this is a mere figure of speech”; the heavens are not inanimate like the four elements of the sublunary world, but are intellectual beings (dhi ‘aql ذي عقل) which literally glorify God with their actions, perhaps consciously. When the heavenly spheres ‘praise God’, it is not really any different from a human being doing the same thing with spoken words, because when we do this, the real praise is in the form of an idea whereas the spoken words are just a vehicle for those ideas.