We’re blogging through St. Thomas Aquinas’ Compendium Theologiae, sometimes called his Shorter Summa. Find the previous posts here.
A body, in philosophical terms, is a material thing that takes up space. Stones, trees, dogs, and human beings are all bodies, that being the most general physical genus on the Tree of Porphyry. God, however, is not this kind of thing.
It is evident, further, that God Himself cannot be a body. For in every body some composition is found, since a body has parts. Hence that which is absolutely simple cannot be a body.
A body is always a composition of some substantial form and prime matter, combined in an act of existence. But we’ve shown that God is absolutely simple, having no composition at all, so God isn’t this kind of thing.
Again, remember that “move”, to Thomas, connotes change of any kind, not simply motion from place to place. But note that phrase in the middle, “as will appear clearly to anyone who examines the matter fully.” I take that to mean that even the sketch of the argument is too long to fit Thomas’ conception of the Compendium—and that’s a point worth remembering. All too often Thomas’ arguments from motion are dismissed by moderns as being too simple, they not realizing that even the longer forms found in the Summa are mere sketches of much longer arguments.
Moreover, we find that a body does not move anything else unless it is first moved itself, as will appear clearly to anyone who examines the matter fully. So if the first mover is absolutely immovable, that being cannot be a body.