54 Lehoux
body itself. Nevertheless, because there is a terminus for falling—a bottom
toward which heavy bodies move—we need an explanation for why the
cosmos has not simply achieved a state of stagnancy: all the earth having
fallen to the center, all the water at rest around that hard core, all the air
above the water, and all the fi re having risen up to the outside. We may
be tempted to look to the large class of self- moving beings, living things,
for keeping motion in play, but as Aristotle pointed out these things are
only self- moving in virtue of a large number of prior motions among
the elements themselves. Instead it is the movement of the heavens (and
the sun primary among the heavenly bodies) that produces changes in the
qualities (hot / cold / wet / dry)—and therefore the elements—down here.
But now what keeps the heavens moving? Here Aristotle turned to an
analysis of what we may think of as “chain reactions,” where one thing
moves another that moves another, and so on. If I push a billiard ball with
a cue, the immediate cause of the ball’s motion is the thing that touched it
directly, a bit of chalk on a small piece of felt. But to say the chalk caused
the ball to move is only to tell an insignifi cant part of the story. The chalk
moved because the felt it was rubbed into moved, and the felt moved
because the glue binding it to the cue moved, and the glue moved...
ultimately because I pushed the body of the cue forward. So where does
the chain of causation (and of explanation) end for the cosmos? That
there must be one fi rst, unmoved, mover emerges from a number of con-
siderations.^41 Where the account gets most richly fl eshed out, however,
is in Metaphysics, book 12. The argument runs as follows: there must be
some eternal motion (in our eternal and currently moving universe). This
combines with an argument that there must be some unmoved mover
(lest the chain of causation regress to infi nity) to produce some necessary
fi rst (primary) cause in the chain which is itself unmoved. But what can
move without being itself moved by that which it moves? Does the bil-
liard ball not push back against me to some extent when I strike it with
the cue? Here the answer gets very interesting. “Objects of desire,” Aristo-
tle says, can cause motion without pushing back. Three paragraphs later
he is into a full- fl edged theological account of the prime mover, which is
now characterized as “that for the sake of which” the heavens rotate, as an
unmoved divinity existing without magnitude at the circumference of the
very cosmos and causing all heavenly spherical motion. Aristotle’s physics
necessitates a god as a fi rst and eternal cause for all motion.
The Stoics took this one step further, identifying god not with the
beginning of a causal chain, but as physically identical to the entirety of
the cosmos itself. Moreover, since the cosmos is the highest order possible,
and since it is itself divine, it must also be rational. Not just rationally