Of things that exist, some exist by nature, some from other causes.

    "By nature" the animals and their parts exist, and the plants and
the simple bodies (earth, fire, air, water)-for we say that these
and the like exist "by nature".

    All the things mentioned present a feature in which they differ from
things which are not constituted by nature. Each of them has within
itself a principle of motion and of stationariness (in respect of
place, or of growth and decrease, or by way of alteration). On the
other hand, a bed and a coat and anything else of that sort, qua
receiving these designations i.e. in so far as they are products of
art-have no innate impulse to change. But in so far as they happen
to be composed of stone or of earth or of a mixture of the two, they
do have such an impulse, and just to that extent which seems to
indicate that nature is a source or cause of being moved and of
being at rest in that to which it belongs primarily, in virtue of
itself and not in virtue of a concomitant attribute.

    I say "not in virtue of a concomitant attribute", because (for
instance) a man who is a doctor might cure himself. Nevertheless it is
not in so far as he is a patient that he possesses the art of
medicine: it merely has happened that the same man is doctor and
patient-and that is why these attributes are not always found
together. So it is with all other artificial products. None of them
has in itself the source of its own production. But while in some
cases (for instance houses and the other products of manual labour)
that principle is in something else external to the thing, in others
those which may cause a change in themselves in virtue of a
concomitant attribute-it lies in the things themselves (but not in
virtue of what they are).

    "Nature" then is what has been stated. Things "have a nature"which
have a principle of this kind. Each of them is a substance; for it
is a subject, and nature always implies a subject in which it inheres.

    The term "according to nature" is applied to all these things and
also to the attributes which belong to them in virtue of what they
are, for instance the property of fire to be carried upwards-which
is not a "nature" nor "has a nature" but is "by nature" or
"according to nature".

    What nature is, then, and the meaning of the terms "by nature" and
"according to nature", has been stated. That nature exists, it would
be absurd to try to prove; for it is obvious that there are many
things of this kind, and to prove what is obvious by what is not is
the mark of a man who is unable to distinguish what is self-evident
from what is not. (This state of mind is clearly possible. A man blind
from birth might reason about colours. Presumably therefore such
persons must be talking about words without any thought to
correspond.)

    Some identify the nature or substance of a natural object with
that immediate constituent of it which taken by itself is without
arrangement, e.g. the wood is the "nature" of the bed, and the
bronze the "nature" of the statue.

    As an indication of this Antiphon points out that if you planted a
bed and the rotting wood acquired the power of sending up a shoot,
it would not be a bed that would come up, but wood-which shows that
the arrangement in accordance with the rules of the art is merely an
incidental attribute, whereas the real nature is the other, which,
further, persists continuously through the process of making.

    But if the material of each of these objects has itself the same
relation to something else, say bronze (or gold) to water, bones (or
wood) to earth and so on, that (they say) would be their nature and
essence. Consequently some assert earth, others fire or air or water
or some or all of these, to be the nature of the things that are.
For whatever any one of them supposed to have this character-whether
one thing or more than one thing-this or these he declared to be the
whole of substance, all else being its affections, states, or
dispositions. Every such thing they held to be eternal (for it could
not pass into anything else), but other things to come into being
and cease to be times without number.

    This then is one account of "nature", namely that it is the
immediate material substratum of things which have in themselves a
principle of motion or change.

    Another account is that "nature" is the shape or form which is
specified in the definition of the thing.

    For the word "nature" is applied to what is according to nature
and the natural in the same way as "art" is applied to what is
artistic or a work of art. We should not say in the latter case that
there is anything artistic about a thing, if it is a bed only
potentially, not yet having the form of a bed; nor should we call it a
work of art. The same is true of natural compounds. What is
potentially flesh or bone has not yet its own "nature", and does not
exist until it receives the form specified in the definition, which we
name in defining what flesh or bone is. Thus in the second sense of
"nature" it would be the shape or form (not separable except in
statement) of things which have in themselves a source of motion. (The
combination of the two, e.g. man, is not "nature" but "by nature" or
"natural".)

    The form indeed is "nature" rather than the matter; for a thing is
more properly said to be what it is when it has attained to fulfilment
than when it exists potentially. Again man is born from man, but not
bed from bed. That is why people say that the figure is not the nature
of a bed, but the wood is-if the bed sprouted not a bed but wood would
come up. But even if the figure is art, then on the same principle the
shape of man is his nature. For man is born from man.

    We also speak of a thing's nature as being exhibited in the
process of growth by which its nature is attained. The "nature" in
this sense is not like "doctoring", which leads not to the art of
doctoring but to health. Doctoring must start from the art, not lead
to it. But it is not in this way that nature (in the one sense) is
related to nature (in the other). What grows qua growing grows from
something into something. Into what then does it grow? Not into that
from which it arose but into that to which it tends. The shape then is
nature.

    "Shape" and "nature", it should be added, are in two senses. For the
privation too is in a way form. But whether in unqualified coming to
be there is privation, i.e. a contrary to what comes to be, we must
consider later.