[The following passage, from one of Aristotle's biological works, treats the role played by teleology in the scientific inquiry into living things. The basic question Aristotle poses is, what is the best way to explain the three kinds of animal parts - the elements of fire, air, earth, and water, that are the fundamental constituents of matter; the homogenous substances, such as blood, bone, and viscera, that form when the basic elements mix in certain ratios, and the heterogeneous organs, such as limbs, eyes, and so forth that are comprised by definite mixtures of the homogenous substances. It is, of course, possible to describe the chains of efficient causes and effects by means of which the organic parts come together in their characteristic ways. But such mechanistic explanation in terms of efficient causality is only a secondary theme in the entire story of organic life. If we to understand the parts fully, we must grasp the role that they play in the total functioning of the living organism. This is what Aristotle calls the "form" (eidos) of the living thing. He is careful to warn us that organic form is not the same thing as shape or color. The form of a living thing is not statically spatial; it is a dynamic process, an act of self-accomplishment that unfolds in time. As an ergon, a mode of working or functioning, the form is the telos, the end that all of the organisms parts and partial processes serve. The efficient causal relations that produce such parts and partial processes have what Aristotle calls a "hypothetical necessity." That is to say, they must exist if the whole organism is to exist, but they exist for the sake of the organism, and not the organism for their sake. Efficient causality takes second place to teleological causality.]
Another matter which must not be
passed over without consideration is, whether the proper subject of our
exposition is that with which the ancient writers concerned themselves, namely,
what is the process of formation of each animal; or whether it is not rather,
what are the characters of a given creature when formed. For there is no small
difference between these two views. The best course appears to be that we should
follow the method already mentioned, and begin with the phenomena presented by
each group of animals, and, when this is done, proceed afterwards to state the
causes of those phenomena, and to deal with their evolution. For elsewhere, as
for instance in house building, this is the true sequence. The plan of the
house, or the house, has this and that form; and because it has this and that
form, therefore is its construction carried out in this or that manner. For the
process of evolution is for the sake of the thing Anally evolved, and not this
for the sake of the process. Empedocles, then, was in error when he said that
many of the characters presented by animals were merely the results of
incidental occurrences during their development; for instance, that the backbone
was divided as it is into vertebrae, because it happened to be broken owing to
the contorted position of the foetus in the womb. In so saying he overlooked the
fact that propagation implies a creative seed endowed with certain formative
properties. Secondly, he neglected another fact, namely, that the parent animal
pre-exists, not only in idea, but actually in time. For man is generated from
man; and thus it is the possession of certain characters by the parent that
determines the development of like characters in the child. The same statement
holds good also for the operations of art, and even for those which are
apparently spontaneous. For the same result as is produced by art may occur
spontaneously. Spontaneity, for instance, may bring about the restoration of
health. The products of art, however, require the pre-existence of an efficient
cause homogeneous with themselves, such as the statuary's art, which must
necessarily precede the statue; for this cannot possibly be produced
spontaneously. Art indeed consists in the conception of the result to be
produced before its realization in the material. As with spontaneity, so with
chance; for this also produces the same result as art, and by the same process.
The fittest mode, then, of
treatment is to say, a man has such and such parts, because the conception of a
man includes their presence, and because they are necessary conditions of his
existence, or, if we cannot quite say this, which would be best of all, then the
next thing to it, namely, that it is either quite impossible for him to exist
without them, or, at any rate, that it is better for him that they should be
there; and their existence involves the existence of other antecedents. Thus we
should say, because man is an animal with such and such characters, therefore is
the process of his development necessarily such as it is; and therefore is it
accomplished in such and such an order, this part being formed first, that next,
and so on in succession; and after a like fashion should we explain the
evolution of all other works of nature.
Now that with which the ancient
writers, who first philosophized about Nature, busied themselves, was the
material principle and the material cause. They inquired what this is, and what
its character; how the universe is generated out of it, and by what efficient
influence, whether, for instance, by antagonism or friendship, whether by
intelligence or spontaneous action, the substratum of matter being assumed to
have certain inseparable properties; fire, for instance, to have a hot nature,
earth a cold one; the former to be light, the latter heavy. For even the genesis
of the universe is thus explained by them. After a like fashion do they deal
also with the development of plants and of animals. They say, for instance, that
the water contained in the body causes by its currents the formation of the
stomach and the other receptacles of food or of excretion; and that the breath
by its passage breaks open the outlets of the nostrils; air and water being the
materials of which bodies are made; for all represent nature as composed of such
or similar substances.
But if men and animals and their
several parts are natural phenomena, then the natural philosopher must take into
consideration not merely the ultimate substances of which they are made, but
also flesh, bone, blood, and all other homogeneous parts; not only these, but
also the heterogeneous parts, such as face, hand, foot; and must examine how
each of these comes to be what it is, and in virtue of what force. For to say
what are the ultimate substances out of which an animal is formed, to state, for
instance, that it is made of fire or earth, is no more sufficient than would be
a similar account in the case of a couch or the like. For we should not be
content with saying that the couch was made of bronze or wood or whatever it
might be, but should try to describe its design or mode of composition in
preference to the material; or, if we did deal with the material, it would at
any rate be with the concretion of material and form. For a couch is such and
such a form embodied in this or that matter, or such and such a matter with this
or that form; so that its shape and structure must be included in our
description. For the formal nature is of greater importance than the material
nature.
Does, then, configuration and
colour constitute the essence of the various animals and of their several parts?
For if so, what Democritus says will be strictly correct. For such appears to
have been his notion. At any rate he says that it is evident to every one what
form it is that makes the man, seeing that he is recognizable by his shape and
colour. And yet a dead body has exactly the same configuration as a living one;
but for all that is not a man. So also no hand of bronze or wood or constituted
in any but the appropriate way can possibly be a hand in more than name. For
like a physician in a painting, or like a flute in a sculpture, in spite of its
name it will be unable to do the office which that name implies. Precisely in
the same way no part of a dead body, such I mean as its eye or its hand, is
really an eye or a hand. To say, then, that shape and colour constitute the
animal is an inadequate statement, and is much the same as if a woodcarver were
to insist that the hand he had cut out was really a hand. Yet the physiologists,
when they give an account of the development and causes of the animal form,
speak very much like such a craftsman. What, however, I would ask, are the
forces by which the hand or the body was fashioned into its shape? The
woodcarver will perhaps say, by the axe or the auger; the physiologist, by air
and by earth. Of these two answers the artificer's is the better, but it is
nevertheless insufficient. For it is not enough for him to say that by the
stroke of his tool this part was formed into a concavity, that into a flat
surface; but he must state the reasons why he struck his blow in such a way as
to effect this, and what his final object was; namely, that the piece of wood
should develop eventually into this or that shape. It is plain, then, that the
teaching of the old physiologists is inadequate, and that the true method is to
state what the definitive characters are that distinguish the animal as a whole;
to explain what it is both in substance and in form, and to deal after the same
fashion with its several organs; in fact, to proceed in exactly the same way as
we should do, were we giving a complete description of a couch.
If now this something that
constitutes the form of the living being be the soul, or part of the soul, or
something that without the soul cannot exist; as would seem to be the case,
seeing at any rate that when the soul departs, what is left is no longer a
living animal, and that none of the parts remain what they were before,
excepting in mere configuration, like the animals that in the fable are turned
into stone; if, I say, this be so, then it will come within the province of the
natural philosopher to inform himself concerning the soul, and to treat of it,
either in its entirety, or, at any rate, of that part of it which constitutes
the essential character of an animal; and it will be his duty to say what this
soul or this part of a soul is; and to discuss the attributes that attach to
this essential character, especially as nature is spoken of in two senses, and
the nature of a thing is either its matter or its essence; nature as essence
including both the motor cause and the final cause. Now it is in the latter of
these two senses that either the whole soul or some part of it constitutes the
nature of an animal; and inasmuch as it is the presence of the soul that enables
matter to constitute the animal nature, much more than it is the presence of
matter which so enables the soul, the inquirer into nature is bound on every
ground to treat of the soul rather than of the matter. For though the wood of
which they are made constitutes the couch and the tripod, it only does so
because it is capable of receiving such and such a form.
What has been said suggests the
question, whether it is the whole soul or only some part of it, the
consideration of which comes within the province of natural science. Now if it
be of the whole soul that this should treat, then there is no place for any
other philosophy beside it. For as it belongs in all cases to one and the same
science to deal with correlated subjects-one and the same science, for instance,
deals with sensation and with the objects of sense-and as therefore the
intelligent soul and the objects of intellect, being correlated, must belong to
one and the same science, it follows that natural science will have to include
the whole universe in its province. But perhaps it is not the whole soul, nor
all its parts collectively, that constitutes the source of motion; but there may
be one part, identical with that in plants, which is the source of growth,
another, namely the sensory part, which is the source of change of quality,
while still another, and this not the intellectual part, is the source of
locomotion. I say not the intellectual part; for other animals than man have the
power of locomotion, but in none but him is there intellect. Thus then it is
plain that it is not of the whole soul that we have to treat. For it is not the
whole soul that constitutes the animal nature, but only some part or parts of
it. Moreover, it is impossible that any abstraction can form a subject of
natural science, seeing that everything that Nature makes is means to an end.
For just as human creations are the products of art, so living objects are
manifest in the products of an analogous cause or principle, not external but
internal, derived like the hot and the cold from the environing universe. And
that the heaven, if it had an origin, was evolved and is maintained by such a
cause, there is therefore even more reason to believe, than that mortal animals
so originated. For order and definiteness are much more plainly manifest in the
celestial bodies than in our own frame; while change and chance are
characteristic of the perishable things of earth. Yet there are some who, while
they allow that every animal exists and was generated by nature, nevertheless
hold that the heaven was constructed to be what it is by chance and spontaneity;
the heaven, in which not the faintest sign of haphazard or of disorder is
discernible! Again, whenever there is plainly some final end, to which a motion
tends should nothing stand in the way, we always say that such final end is the
aim or purpose of the motion; and from this it is evident that there must be a
something or other really existing, corresponding to what we call by the name of
Nature. For a given germ does not give rise to any chance living being, nor
spring from any chance one; but each germ springs from a definite parent and
gives rise to a definite progeny. And thus it is the germ that is the ruling
influence and fabricator of the offspring. For these it is by nature, the
offspring being at any rate that which in nature will spring from it. At the
same time the offspring is anterior to the germ; for germ and perfected progeny
are related as the developmental process and the result. Anterior, however, to
both germ and product is the organism from which the germ was derived. For every
germ implies two organisms, the parent and the progeny. For germ or seed is both
the seed of the organism from which it came, of the horse, for instance, from
which it was derived, and the seed of the organism that will eventually arise
from it, of the mule, for example, which is developed from the seed of the
horse. The same seed then is the seed both of the horse and of the mule, though
in different ways as here set forth. Moreover, the seed is potentially that
which will spring from it, and the relation of potentiality to actuality we
know.
There are then two causes,
namely, necessity and the final end. For many things are produced, simply as the
results of necessity. It may, however, be asked, of what mode of necessity are
we speaking when we say this. For it can be of neither of those two modes which
are set forth in the philosophical treatises. There is, however, the third mode,
in such things at any rate as are generated. For instance, we say that food is
necessary; because an animal cannot possibly do without it. This third mode is
what may be called hypothetical necessity. Here is another example of it. If a
piece of wood is to be split with an axe, the axe must of necessity be hard;
and, if hard, must of necessity be made of bronze or iron. Now exactly in the
same way the body, which like the axe is an instrument-for both the body as a
whole and its several parts individually have definite operations for which they
are made-just in the same way, I say, the body, if it is to do its work, must of
necessity be of such and such a character, and made of such and such materials.
It is plain then that there are
two modes of causation, and that both of these must, so far as possible, be
taken into account in explaining the works of nature, or that at any rate an
attempt must be made to include them both; and that those who fail in this tell
us in reality nothing about nature. For primary cause constitutes the nature of
an animal much more than does its matter. There are indeed passages in which
even Empedocles hits upon this, and following the guidance of fact, finds
himself constrained to speak of the ratio (olugos) as constituting the essence
and real nature of things. Such, for instance, is the case when he explains what
is a bone. For he does not merely describe its material, and say it is this one
element, or those two or three elements, or a compound of all the elements, but
states the ratio (olugos) of their combination. As with a bone, so manifestly is
it with the flesh and all other similar parts.
The reason why our predecessors
failed in hitting upon this method of treatment was, that they were not in
possession of the notion of essence, nor of any definition of substance. The
first who came near it was Democritus, and he was far from adopting it as a
necessary method in natural science, but was merely brought to it, spite of
himself, by constraint of facts. In the time of Socrates a nearer approach was
made to the method. But at this period men gave up inquiring into the works of
nature, and philosophers diverted their attention to political science and to
the virtues which benefit mankind.
Of the method itself the
following is an example. In dealing with respiration we must show that it takes
place for such or such a final object; and we must also show that this and that
part of the process is necessitated by this and that other stage of it. By
necessity we shall sometimes mean hypothetical necessity, the necessity, that
is, that the requisite antecedants shall be there, if the final end is to be
reached; and sometimes absolute necessity, such necessity as that which connects
substances and their inherent properties and characters. For the alternate
discharge and re-entrance of heat and the inflow of air are necessary if we are
to live. Here we have at once a necessity in the former of the two senses. But
the alternation of heat and refrigeration produces of necessity an alternate
admission and discharge of the outer air, and this is a necessity of the second
kind.
In the foregoing we have an
example of the method which we must adopt, and also an example of the kind of
phenomena, the causes of which we have to investigate.
. . .