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. ...
Nature then is what has
been stated. Things have a naturewhich 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.
...
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. ...
Part 2
We have distinguished, then, the
different ways in which the term nature is used.
The next point to consider is how
the mathematician differs from the physicist. Obviously
physical bodies contain surfaces and volumes, lines and
points, and these are the subject-matter of mathematics.
Further, is astronomy different
from physics or a department of it? It seems absurd that the
physicist should be supposed to know the nature of sun or
moon, but not to know any of their essential attributes,
particularly as the writers on physics obviously do discuss
their shape also and whether the earth and the world are
spherical or not.
Now the mathematician, though he
too treats of these things, nevertheless does not treat of
them as the limits of a physical body; nor does he consider
the attributes indicated as the attributes of such bodies.
That is why he separates them; for in thought they are
separable from motion, and it makes no difference, nor does
any falsity result, if they are separated. The holders of the
theory of Forms do the same, though they are not aware of it;
for they separate the objects of physics, which are less
separable than those of mathematics. This becomes plain if
one tries to state in each of the two cases the definitions
of the things and of their attributes. Odd and
even, straight and
curved, and likewise number,
line, and figure, do not involve
motion; not so flesh and bone and
man-these are defined like snub nose,
not like curved. ...
Part 3
Now that we have established these
distinctions, we must proceed to consider causes, their
character and number. Knowledge is the object of our inquiry,
and men do not think they know a thing till they have grasped
the why of (which is to grasp its primary cause).
So clearly we too must do this as regards both coming to be
and passing away and every kind of physical change, in order
that, knowing their principles, we may try to refer to these
principles each of our problems.
In one sense, then, (1) that out of
which a thing comes to be and which persists, is called
cause, e.g. the bronze of the statue, the silver
of the bowl, and the genera of which the bronze and the
silver are species.
In another sense (2) the form or
the archetype, i.e. the statement of the essence, and its
genera, are called causes (e.g. of the octave the
relation of 2:1, and generally number), and the parts in the
definition.
Again (3) the primary source of the
change or coming to rest; e.g. the man who gave advice is a
cause, the father is cause of the child, and generally what
makes of what is made and what causes change of what is
changed.
Again (4) in the sense of end or
that for the sake of which a thing is done, e.g.
health is the cause of walking about. (Why is he
walking about? we say. To be healthy, and,
having said that, we think we have assigned the cause.) The
same is true also of all the intermediate steps which are
brought about through the action of something else as means
towards the end, e.g. reduction of flesh, purging, drugs, or
surgical instruments are means towards health. All these
things are for the sake of the end, though they
differ from one another in that some are activities, others
instruments.
This then perhaps exhausts the
number of ways in which the term cause is used.
Such then is the number and nature
of the kinds of cause. ...
OPTIONAL READING OF PARTS 8 & 9
Part 8
We must explain then (1) that
Nature belongs to the class of causes which act for the sake
of something; (2) about the necessary and its place in
physical problems, for all writers ascribe things to this
cause, arguing that since the hot and the cold, &c., are
of such and such a kind, therefore certain things necessarily
are and come to be-and if they mention any other cause (one
his friendship and strife, another his
mind), it is only to touch on it, and then
good-bye to it.
A difficulty presents itself: why
should not nature work, not for the sake of something, nor
because it is better so, but just as the sky rains, not in
order to make the corn grow, but of necessity? What is drawn
up must cool, and what has been cooled must become water and
descend, the result of this being that the corn grows.
Similarly if a mans crop is spoiled on the
threshing-floor, the rain did not fall for the sake of
this-in order that the crop might be spoiled-but that result
just followed. Why then should it not be the same with the
parts in nature, e.g. that our teeth should come up of
necessity-the front teeth sharp, fitted for tearing, the
molars broad and useful for grinding down the food-since they
did not arise for this end, but it was merely a coincident
result; and so with all other parts in which we suppose that
there is purpose? Wherever then all the parts came about just
what they would have been if they had come be for an end,
such things survived, being organized spontaneously in a
fitting way; whereas those which grew otherwise perished and
continue to perish, as Empedocles says his man-faced
ox-progeny did.
Such are the arguments (and others
of the kind) which may cause difficulty on this point. Yet it
is impossible that this should be the true view. For teeth
and all other natural things either invariably or normally
come about in a given way; but of not one of the results of
chance or spontaneity is this true. We do not ascribe to
chance or mere coincidence the frequency of rain in winter,
but frequent rain in summer we do; nor heat in the dog-days,
but only if we have it in winter. If then, it is agreed that
things are either the result of coincidence or for an end,
and these cannot be the result of coincidence or spontaneity,
it follows that they must be for an end; and that such things
are all due to nature even the champions of the theory which
is before us would agree. Therefore action for an end is
present in things which come to be and are by nature.
Further, where a series has a
completion, all the preceding steps are for the sake of that.
Now surely as in intelligent action, so in nature; and as in
nature, so it is in each action, if nothing interferes. Now
intelligent action is for the sake of an end; therefore the
nature of things also is so. Thus if a house, e.g. had been a
thing made by nature, it would have been made in the same way
as it is now by art; and if things made by nature were made
also by art, they would come to be in the same way as by
nature. Each step then in the series is for the sake of the
next; and generally art partly completes what nature cannot
bring to a finish, and partly imitates her. If, therefore,
artificial products are for the sake of an end, so clearly
also are natural products. The relation of the later to the
earlier terms of the series is the same in both. This is most
obvious in the animals other than man: they make things
neither by art nor after inquiry or deliberation. Wherefore
people discuss whether it is by intelligence or by some other
faculty that these creatures work,spiders, ants, and the
like. By gradual advance in this direction we come to see
clearly that in plants too that is produced which is
conducive to the end-leaves, e.g. grow to provide shade for
the fruit. If then it is both by nature and for an end that
the swallow makes its nest and the spider its web, and plants
grow leaves for the sake of the fruit and send their roots
down (not up) for the sake of nourishment, it is plain that
this kind of cause is operative in things which come to be
and are by nature. And since nature means two
things, the matter and the form, of which the latter is the
end, and since all the rest is for the sake of the end, the
form must be the cause in the sense of that for the
sake of which.
Now mistakes come to pass even in
the operations of art: the grammarian makes a mistake in
writing and the doctor pours out the wrong dose. Hence
clearly mistakes are possible in the operations of nature
also. If then in art there are cases in which what is rightly
produced serves a purpose, and if where mistakes occur there
was a purpose in what was attempted, only it was not
attained, so must it be also in natural products, and
monstrosities will be failures in the purposive effort. Thus
in the original combinations the ox-progeny if
they failed to reach a determinate end must have arisen
through the corruption of some principle corresponding to
what is now the seed.
Further, seed must have come into
being first, and not straightway the animals: the words
whole-natured first... must have meant seed.
Again, in plants too we find the
relation of means to end, though the degree of organization
is less. Were there then in plants also olive-headed
vine-progeny, like the man-headed
ox-progeny, or not? An absurd suggestion; yet there
must have been, if there were such things among animals.
Moreover, among the seeds anything
must have come to be at random. But the person who asserts
this entirely does away with nature and what
exists by nature. For those things are natural
which, by a continuous movement originated from an internal
principle, arrive at some completion: the same completion is
not reached from every principle; nor any chance completion,
but always the tendency in each is towards the same end, if
there is no impediment.
The end and the means towards it
may come about by chance. We say, for instance, that a
stranger has come by chance, paid the ransom, and gone away,
when he does so as if he had come for that purpose, though it
was not for that that he came. This is incidental, for chance
is an incidental cause, as I remarked before. But when an
event takes place always or for the most part, it is not
incidental or by chance. In natural products the sequence is
invariable, if there is no impediment.
It is absurd to suppose that
purpose is not present because we do not observe the agent
deliberating. Art does not deliberate. If the ship-building
art were in the wood, it would produce the same results by
nature. If, therefore, purpose is present in art, it is
present also in nature. The best illustration is a doctor
doctoring himself: nature is like that.
It is plain then that nature is a
cause, a cause that operates for a purpose.
Part 9
As regards what is of
necessity, we must ask whether the necessity is
hypothetical, or simple as well. The
current view places what is of necessity in the process of
production, just as if one were to suppose that the wall of a
house necessarily comes to be because what is heavy is
naturally carried downwards and what is light to the top,
wherefore the stones and foundations take the lowest place,
with earth above because it is lighter, and wood at the top
of all as being the lightest. Whereas, though the wall does
not come to be without these, it is not due to these, except
as its material cause: it comes to be for the sake of
sheltering and guarding certain things. Similarly in all
other things which involve production for an end; the product
cannot come to be without things which have a necessary
nature, but it is not due to these (except as its material);
it comes to be for an end. For instance, why is a saw such as
it is? To effect so-and-so and for the sake of so-and-so.
This end, however, cannot be realized unless the saw is made
of iron. It is, therefore, necessary for it to be of iron, it
we are to have a saw and perform the operation of sawing.
What is necessary then, is necessary on a hypothesis; it is
not a result necessarily determined by antecedents. Necessity
is in the matter, while that for the sake of
which is in the definition.
Necessity in mathematics is in a
way similar to necessity in things which come to be through
the operation of nature. Since a straight line is what it is,
it is necessary that the angles of a triangle should equal
two right angles. But not conversely; though if the angles
are not equal to two right angles, then the straight line is
not what it is either. But in things which come to be for an
end, the reverse is true. If the end is to exist or does
exist, that also which precedes it will exist or does exist;
otherwise just as there, if-the conclusion is not true, the
premiss will not be true, so here the end or that for
the sake of which will not exist. For this too is
itself a starting-point, but of the reasoning, not of the
action; while in mathematics the starting-point is the
starting-point of the reasoning only, as there is no action.
If then there is to be a house, such-and-such things must be
made or be there already or exist, or generally the matter
relative to the end, bricks and stones if it is a house. But
the end is not due to these except as the matter, nor will it
come to exist because of them. Yet if they do not exist at
all, neither will the house, or the saw-the former in the
absence of stones, the latter in the absence of iron-just as
in the other case the premisses will not be true, if the
angles of the triangle are not equal to two right angles.
The necessary in nature, then, is
plainly what we call by the name of matter, and the changes
in it. Both causes must be stated by the physicist, but
especially the end; for that is the cause of the matter, not
vice versa; and the end is that for the sake of
which, and the beginning starts from the definition or
essence; as in artificial products, since a house is of
such-and-such a kind, certain things must necessarily come to
be or be there already, or since health is this, these things
must necessarily come to be or be there already. Similarly if
man is this, then these; if these, then those. Perhaps the
necessary is present also in the definition. For if one
defines the operation of sawing as being a certain kind of
dividing, then this cannot come about unless the saw has
teeth of a certain kind; and these cannot be unless it is of
iron. For in the definition too there are some parts that
are, as it were, its matter.