of "natural science" and "natural history," but "nature" by itself, though it is a very ambiguous
word, seldom means just what "phusis" meant. "Phusis" had to do with growth; one might say it is
the "nature" of an acorn to grow into an oak, and in that case one would be using the word in the
Aristotelian sense. The "nature" of a thing, Aristotle says, is its end, that for the sake of which it
exists. Thus the word has a teleological implication. Some things exist by nature, some from other
causes. Animals, plants, and simple bodies (elements) exist by nature; they have an internal
principle of motion. (The word translated "motion" or "movement" has a wider meaning than
"locomotion"; in addition to locomotion it includes change of quality or of size.) Nature is a
source of being moved or at rest. Things "have a nature" if they have an internal principle of this
kind. The phrase "according to nature" applies to these things and their essential attributes. (It was
through this point of view that "unnatural" came to express blame.) Nature is in form rather than
in matter; what is potentially flesh or bone has not yet acquired its own nature, and a thing is more
what it is when it has attained to fulfilment. This whole point of view seems to be suggested by
biology: the acorn is "potentially" an oak.
Nature belongs to the class of causes which operate for the sake of something. This leads to a
discussion of the view that nature works of necessity, without purpose, in connection with which
Aristotle discusses the survival of the fittest, in the form taught by Empedocles. This cannot be
right, he says, because things happen in fixed ways, and when a series has a completion, all
preceding steps are for its sake. Those things are "natural" which "by a continuous movement
originated from an internal principle, arrive at some completion" (199b).
This whole conception of "nature," though it might well seem admirably suited to explain the
growth of animals and plants, became, in the event, a great obstacle to the progress of science, and
a source of much that was bad in ethics. In the latter respect, it is still harmful.
Motion, we are told, is the fulfilling of what exists potentially. This view, apart from other defects,
is incompatible with the relativity of locomotion. When A moves relatively to B, B moves
relatively to A, and there is no sense in saying that one of the two is in motion while the other is at
rest. When a dog seizes a bone, it seems to common