Of God and His Creatures

In chapter XXII it is argued that the movement of the heavenly spheres goes to engender things on earth (motio ipsius coeli ordinatur ad generationem). In chapter XXIII it is argued that the movements of the heavenly spheres are not done mechanically, but are set up and kept going by intelligence, the star-bearing spheres being either all moved by God, or all by angels at His bidding, or all by the primum mobile, the primum mobile itself being either moved by God, or by an angel, or having a soul of its own, but in any case obeying God. "It makes no difference," says St Thomas, "to our present purpose, whether the heavenly sphere is moved by a subsistent intelligence united with it as a soul, or by an intelligence subsisting apart; and whether each of the heavenly spheres is moved by God, or whether none of them is moved by Him immediately, but they are moved mediately through created spirits; or whether the first alone is moved immediately by God, and the others through the medium of created spirits; provided it be held that the movement of the heavens is the work of spirit."

Of God and His Creatures: 3.21