Marsilio Ficino’s Platonic Theology, Volume II

3Indeed, those parts will not be parts of another body at all, precisely because each will exist in its own actuality. Each will instead subsist as a complete thing by itself, and there will be an infinite multitude of little bodies existing in actuality. But no such multitude can exist in nature. Since, therefore, the parts of a body cannot be actually infinite—and indeed cannot, in truth, even exist in actuality at all, since they have no being of their own but are contained under the being of the composite whole—it follows that the parts of a body do not move themselves. Otherwise they would be forced for that reason to exist in actuality and to be actually infinite without qualification. Let us conclude, then, that body cannot be truly and primarily self-moving, since this cannot belong to it throughout itself when its parts cannot attain self-motion.

4Let us approach the same conclusion again by another path. When someone asserts that a body moves itself, he is compelled to admit one chiefly among four possibilities: one part of the body is moved by another; the whole is moved by a part; a part is moved by the whole; or the whole is moved by the whole—that is, all the parts by all the parts. If the first is affirmed, since one part is one thing and the other another, the same thing will not move itself; one thing will instead move another. Nor on this account will the composite body truly move itself, since it is constituted of parts that do not move themselves. It will merely contain two things distinct from one another, one of which moves the other. If you accept the second member of the division, namely that a part moves the whole, or the third, that the whole moves a part, the composite still does not truly move itself. For we take a part to be one thing and the whole another. And the part that moves the whole must move every part; consequently, among the other parts it also changes itself.