And since that which is moved must be moved by something, and the first mover must be in itself unmovable, and eternal movement must be produced by something eternal and a single movement by a single thing, and since we see that besides the simple spatial movement of the universe, which we say the first and unmovable substance produces, there are other spatial movements those of the planets which are eternal (for the body which moves in a circle is eternal and unresting; we have proved these points in the Physi, each of these movements also must be caused by a substance unmovable in itself and eternal.