Natural Knowledge in the Classical World 53this could- have- been- otherwise argument, that Galen sees himself as re-
sponding in On the Usefulness of the Parts of the Body:
The atoms or indivisible bodies which some posit as elements are not, accord-
ing to these very men, naturally formed into whole [bodies] by an external
force or by anything permeating them. They are left, then, to build the
structure of perceptible bodies by a random interweaving with one another.
But a random interweaving almost never produces a useful artifact, but usu-
ally something useless and silly. This is why men who claim that the primary
elements are the kinds of things atomists say they are, are unwilling to think
that Nature is skillful; for in spite of the fact that they clearly see as soon as
they look at an animal’s body that it has no part without a use, they try to
fi nd just one thing that will serve for contradiction, either at fi rst glance or
from dissection. Consequently, they have imposed on me the necessity of
explaining all the parts and of extending the discussion even to things that
are not necessary for the treatment, prognosis, or diagnosis of disease.^38Hence his completeness: if a single counterexample would satisfy his
opponents, Galen could afford to leave no stone unturned. Notice here
that he referred to a knowledge of anatomy as also being useful for the
physician in his day- to- day practice, a claim that not all of Galen’s con-
temporaries would take for granted, and a claim for which he argued ex-
plicitly in other works.^39
GODS
The centrality of divinity in Galen’s teleological argument was direct and
immediate. The purposiveness of Nature, her wisdom, her foresight, her
careful planning emerged as more than metaphors in his work. The ob-
viousness of intentional design was demonstrated at every level of obser-
vation, and the force of this idea seemed to strengthen the farther and
farther Galen moved into the body. For Aristotle before him, divinity had
also played a central role in nature, even though it came in only after
a number of other considerations. Aristotle argued that the stuff of the
heavens, with its eternal and unchanging natural circular motion, was
superior to the stuff of our changeable sublunary world, even claiming
that the farther away from our changeable world, the better the matter
would be.^40 But all motion requires a cause, either internal to the object
itself (as when animals walk) or external (as when balls are kicked by
children). When heavy bodies fall, that is a natural motion internal to the