48 Lehoux
the fact that something is hiding in there in abeyance. But it does not
cover an ignorance of what that something is. Potential turns out to be
an explanatorily rich notion, playing a prominent role in Aristotelian ac-
counts of change. In development, it explains how a small seed can grow
to become a large (and very different) adult plant. The seed does not actu-
ally contain leaves and a trunk, but it does in potential, and the process
of development is just the actualization of that potential. But this process
of actualization depends on a kind of end- driven process, where the seed
has some power within it that pushes it toward that actualization, that
end product. One may be tempted to ask chicken- and- egg questions at
this point, but Aristotle put a stop to that by arguing that the mature form
of the plant or animal is prior (not just temporally, but hierarchically) to
the seed it produces.^23 Moreover, the process of change from seed to adult,
even though aiming at an end, was one driven internally, within the seed
itself, by nature—where nature just is this process of self- change.^24 This
means that concepts of nature and of (for example, human) artifi ce are
both defi ned in terms of change: the one driven internally, within the
organism or object itself (the growth and decay of plants, the heaviness
of rocks), and the other driven externally, by the imposition of force from
without (human craftsmanship for example, but also a dog picking up a
stick against the stick’s natural inclination to fall down).
This way of understanding development was not universally adopted
in antiquity, but aspects of it were widespread. In particular, the use of
teleological explanations (explanations that use the end- toward- which
something happens as some kind of cause) in biology had—and contin-
ues to have—a very long history.^25 One prominent principle that emerged
in tandem with teleology and that dominated much ancient thought, not
just in biology but in the sciences in general, was the maxim that nature
does nothing in vain.^26 This maxim works as a hermeneutic, guiding the
investigator to pay attention to every smallest detail, since all are relevant
to an understanding of nature, and all are purposive.EXPERIMENT AND OBSERVATION
Both this purposiveness and this demand for extreme attention to detail
come out very clearly in the work of Ptolemy’s contemporary, the second-
century CE anatomist and physician (perhaps the single greatest of each
in antiquity), Galen.^27 Five centuries before Galen, Aristotle himself had
performed anatomies on a wide range of animals and fi shes, although his