by Aristotle
Furthermore, living beings cannot be divided by the functions common to body and soul, by Flying, for instance, and Walking, as we see them divided in the dichotomies already referred to. For some groups, Ants for instance, fall under both [643b1] divisions, some ants flying while others do not. Similarly as regards the division into Wild and Tame; for it also would involve the disruption of a species into different groups. For in almost all species in which some members are tame, there are other [5] members that are wild. Such, for example, is the case with Men, Horses, Oxen, Dogs in India, Pigs, Goats, Sheep: groups which if they have the same name, have not been divided, and which, if single, prove that Wildness and Tameness do not amount to specific differences. And whatever differentia we take as a basis of division the same difficulty will occur.
We must attempt to recognize the natural groups, following the indications [10] afforded by the instincts of mankind, which led them for instance to form the class of Birds and the class of Fishes, each of which groups combines a multitude of differentiae, and is not defined by a single one as in dichotomy. The method of dichotomy is either impossible (for it would put a single group under different [15] divisions or contrary groups under the same division), or it only furnishes a single differentia for each species, which either alone or in combination has to constitute the ultimate species.
If, again, they do not take a differentia of the differentia, they are bound to make their division continuous only in the sense in which a sentence is one by conjunction. For instance, suppose we have the bifurcation Feathered and Featherless, [20] and then divide Feathered into Wild and Tame, or into White and Black. Tame and White are not a differentiation of Feathered, but are the commencement of an independent bifurcation, and are here by accident.
As we said then, we must define at the outset by a multiplicity of differentiae. [25] If we do so, privative terms will be available, which are unavailable to the dichotomist.
The impossibility of reaching the definition of any of the ultimate forms by dichotomy of the larger group, as some propose, is manifest also from the following considerations. It is impossible that a single differentia, either by itself or in [30] combination shall express the whole of a species. [In saying a single differentia by itself I mean one which has no differentia as Cleft-footed; in saying a single differentia in combination I mean, to give an instance, Many-cleft-footed as related to Cleft-footed.]3 The very continuity of a series of successive differentiae in a [35] division is intended to show that the whole is a unity. But one is misled by the usages of language into imagining that it is merely the final term of the series [Many-cleft-footed or Two-footed for instance]4 that constitutes the whole differentia, [and [644a1] that Footed Cleft-footed, are superfluous]5 Now it is evident that such a series cannot consist of many terms. For if one divides and subdivides, one soon reaches the final differential term, [but for all that will not have got to the ultimate division, [5] that is, to the species.]6 Suppose, for example, Man to be the animal to be defined; the single differentia will be Cleft-footed, either by itself or with its antecedents, Footed and Two-footed. Now if man was nothing more than a Cleft-footed animal, this single differentia would duly represent his essence. But seeing that this is not the case, more differentiae than this one will necessarily be required to define him; and these cannot come under one division; for each single branch of a dichotomy [10] ends in a single differentia, and cannot possibly include several differentiae belonging to one and the same animal.
It is impossible then to reach any of the ultimate animal forms by dichotomous division.
4 · It deserves inquiry why a single name denoting a higher group was not invented by mankind, as an appellation to comprehend the two groups of Water [15] animals and Winged animals. For even these have certain attributes in common. However, the present nomenclature is just. Groups that only differ in degree, and in the more or less of an identical element that they possess, are aggregated under a single class; groups whose attributes are only analogous are separated. For instance, bird differs from bird by gradation, or by excess and defect—some birds have long [20] feathers, others short ones. Bird and Fish only agree in having analogous organs; for what in the bird is feather, in the fish is scale. It is not easy to do this in all cases; for in most animals what is common is so by analogy.
Since the ultimate species are substances and individuals which do not differ in species are found in them (e.g. Socrates, Coriscus), we must either describe the [25] universal attributes first or else say the same thing many time over, as I said. (The universal attributes are common; for we call universal those which belong to more than one subject.)
One may wonder which of two courses to follow. For on the one hand it may be urged that as the ultimate species represent substances, it will be well, if practicable, to examine these ultimate species separately, as Man, and Bird—for [30] this genus contains species: about every indivisible species, then, e.g. Sparrow, Crane, and the like.
On the other hand, however, this course would involve repeated mention of the same attribute, as the same attribute is common to many species, and so far would be somewhat irrational and tedious. Perhaps, then, it will be best to treat generically [644b1] the universal attributes of the groups that have a common nature and contain closely allied subordinate forms, whether they are groups recognized by popular usage, such as Birds and Fishes, or groups not popularly known by a common [5] appellation, but composed of closely allied subordinate groups; and only to deal individually with the attributes of a single species, when such species—man, for instance, and any other such, if such there be—are not of that sort.
It is generally similarity in the shape of particular organs, or of the whole body, that has determined the formation of the larger groups. It is in virtue of such a similarity that Birds, Fishes, Cephalopoda, and Testacea have been made to form [10] each a separate class. For within the limits of each such class, the parts do not differ in that they have no nearer resemblance than that of analogy—such as exists between the bone of man and the spine of fish—but differ merely in respect of such corporeal conditions as largeness smallness, softness hardness, smoothness roughness, and other similar oppositions, or, in one word, in respect of degree. [15]
We have now touched upon the canons for criticizing the method of natural science, and have considered what is the most systematic and easy course of investigation; we have also dealt with division, and the mode of conducting it so as best to attain the ends of science, and have shown why dichotomy is either impracticable or inefficacious for its professed purposes.
Having laid this foundation, let us pass on to our next topic. [20]
5 · Of substances constituted by nature some are ungenerated, imperishable, and eternal, while others are subject to generation and decay. The former are excellent and divine, but less accessible to knowledge. The evidence that might [25] throw light on them, and on the problems which we long to solve respecting them, is furnished but scantily by sensation; whereas respecting perishable plants and animals we have abundant information, living as we do in their midst, and ample [30] data may be collected concerning all their various kinds, if only we are willing to take sufficient pains. Both departments, however, have their special charm. The scanty conceptions to which we can attain of celestial things give us, from their excellence, more pleasure than all our knowledge of the world in which we live; just as a half glimpse of persons that we love is more delightful than an accurate view of [645a1] other things, whatever their number and dimensions. On the other hand, in certitude and in completeness our knowledge of terrestrial things has the advantage. Moreover, their greater nearness and affinity to us balances somewhat the loftier interest of the heavenly things that are the objects of the higher philosophy. Having [5] already treated of the celestial world, as far as our conjectures could reach, we proceed to treat of animals, without omitting, to the best of our ability, any member of the kingdom, however ignoble. For if some have no graces to charm
the sense, yet nature, which fashioned them, gives amazing pleasure in their study to all who can [10] trace links of causation, and are inclined to philosophy. Indeed, it would be strange if mimic representations of them were attractive, because they disclose the mimetic skill of the painter or sculptor, and the original realities themselves were not more [15] interesting, to all at any rate who have eyes to discern the causes. We therefore must not recoil with childish aversion from the examination of the humbler animals. Every realm of nature is marvellous: and as Heraclitus, when the strangers who came to visit him found him warming himself at the furnace in the kitchen and [20] hesitated to go in, is reported to have bidden them not to be afraid to enter, as even in that kitchen divinities were present, so we should venture on the study of every kind of animal without distaste; for each and all will reveal to us something natural and something beautiful. Absence of haphazard and conduciveness of everything to an end are to be found in nature’s works in the highest degree, and the end for which [25] those works are put together and produced is a form of the beautiful.
If any person thinks the examination of the rest of the animal kingdom an unworthy task, he must hold in like disesteem the study of man. For no one can look at the elements of the human frame—blood, flesh, bones, vessels, and the [30] like—without much repugnance. Moreover, when any one of the parts or structures, be it which it may, is under discussion, it must not be supposed that it is its material composition to which attention is being directed or which is the object of the discussion, but rather the total form. Similarly, the true object of architecture is not bricks, mortar, or timber, but the house; and so the principal object of natural philosophy is not the material elements, but their composition, and the totality of [645b1] the substance, independently of which they have no existence.
The course of exposition must be first to state the essential attributes common to whole groups of animals, and then to attempt to give their explanation. Many groups, as already noticed, present common attributes, that is to say, in some cases [5] absolutely identical—feet, feathers, scales, and the like; while in other groups the affections and organs are analogous. For instance, some groups have lungs, others have no lung, but an organ analogous to a lung in its place; some have blood, others [10] have no blood, but a fluid analogous to blood, and with the same office. To treat of the common attributes separately in connexion with each individual group would involve, as already suggested, useless iteration. For many groups have common attributes. So much for this topic.
As every instrument and every bodily member is for the sake of something, viz. [15] some action, so the whole body must evidently be for the sake of some complex action. Thus the saw is made for sawing, for sawing is a function, and not sawing for the saw. Similarly, the body too must somehow or other be made for the soul, and each part of it for some subordinate function, to which it is adapted. [20]
We have, then, first to describe the common functions, and those which belong to a genus or to a species. By ‘common’ I mean those which belong to all animals; by to a genus’, those of animals whose differences from one another we see to be matters of degree—Bird is a genus. Man is a species, and so is everything not [25] differentiated into subordinate groups. In the first case the common attributes may be called analogous, in the second generic, in the third specific.
When a function is ancillary to another, a like relation manifestly obtains between the organs which discharge these functions; and similarly, if one function is prior to and the end of another, their respective organs will stand to each other in [30] the same relation. Thirdly, there are functions which are the necessary consequences of others.
Instances of what I mean by functions and affections are Reproduction, Growth, Copulation, Waking, Sleep, Locomotion, and other similar animal actions. Instances of what I mean by parts are Nose, Eye, Face, and other so-called [646a1] members; and similarly for the rest. So much for the method to be pursued. Let us now try to set forth the causes of all these things, both common and special, and in so doing let us follow that order of exposition which conforms, as we have indicated, to the order of nature.
BOOK II
1 · The nature and the number of the parts of which animals are severally composed are matters which have already been set forth in detail in the book of Histories about animals. We have now to inquire what are the causes that in each [10] case have determined this composition, a subject quite distinct from that dealt with in the Histories.
Now there are three degrees of composition; and of these the first in order, as all will allow, is composition out of what some call the elements, such as earth, air, water, fire. Perhaps, however, it would be more accurate to say composition out of [15] the elementary forces; nor indeed out of all of these, as said elsewhere in previous treatises. For wet and dry, hot and cold, form the material of all composite bodies; and all other differences are secondary to these, such differences, that is, as heaviness or lightness, density or rarity, roughness or smoothness, and any other [20] such properties of bodies as there may be. The second degree of composition is that by which the homogeneous parts of animals, such as bone, flesh, and the like, are constituted out of the primary substances. The third and last stage is the composition which forms the heterogeneous parts, such as face, hand, and the rest.
[25] Now the order of development and the order of substance are always the inverse of each other. For that which is posterior in the order of development is antecedent in the order of nature, and that is genetically last which in nature is first.
(That this is so is manifest by induction; for a house does not exist for the sake of bricks and stones, but these materials for the sake of the house; and the same is [30] the case with the materials of other bodies. And the same thing can be shown by argument. For generation is a process from something to something, from a principle to a principle—from the primary efficient cause, which is something already endowed with a certain nature, to some definite form or similar end; for [35] man generates man, and plant generates plant, in each case out of the underlying material.)
[646b1] In order of time, then, the material and the generative process must necessarily be anterior; but in logical order the substance and form of each being precedes the material. This is evident if one only tries to define the process of formation. For the definition of house-building includes that of the house; but the definition of the [5] house does not include that of house-building; and the same is true of all other productions. So that it must necessarily be that the elementary material exists for the sake of the homogeneous parts, seeing that these are genetically posterior to it, just as the heterogeneous parts are posterior genetically to them. For these heterogeneous parts have reached the end and goal, having the third degree of [10] composition, in which development often attains its final term.
Animals, then, are composed of homogeneous parts, and are also composed of heterogeneous parts. The former, however, exist for the sake of the latter. For the active functions and operations of the body are carried on by these; that is, by the heterogeneous parts, such as the eye, the nostril, the whole face, the fingers, the [15] hand, and the whole arm. But inasmuch as there is a great variety in the functions and motions not only of the whole animal but also of the individual organs, it is necessary that the substances out of which these are composed shall present a diversity of powers. For some purposes softness is advantageous, for others hardness; some parts must be capable of extension, others of flexion. Such powers, [20] then, are distributed separately to the different homogeneous parts, one being soft another hard, one wet another dry, one viscous another brittle; whereas each of the heterogeneous parts presents a combination of multifarious powers. For the hand, to take an example, requires one power to enable it to effect pressure, and another [25] for simple prehension. For this reason the instrumental parts of the body are compounded out of bones, sinews, flesh, and the like, but not these latter out of the former.
So far, then, as ha
s yet been stated, the relations between these two orders of parts are determined by a final cause. We have, however, to inquire whether necessity may not also have a share in the matter; and it must be admitted that these [30] mutual relations could not from the very beginning have possibly been other than they are. For heterogeneous parts can be made up out of homogeneous parts, either from a plurality of them, or from a single one, as is the case with some of the viscera which, varying in configuration, are yet, to speak broadly, formed from a single homogeneous substance; but that homogeneous substances should be formed out of a combination of heterogeneous parts is clearly an impossibility—for then a homogeneous thing would consist of many heterogeneous things. For these causes, then, some parts of animals are simple and homogeneous, while others are [647a1] composite and heterogeneous; and dividing the parts into the instrumental and the sensitive, each one of the former is, as before said, heterogeneous, and each one of [5] the latter homogeneous. For each sense is confined to a single order of sensibles, and its organ must be such as to admit that order. But that which is endowed with a property potentially acted on by that which has the like property actually, so that the two are the same in kind, and if the latter is single so also is the former. Thus it is [10] that while no physiologists ever dream of saying of the hand or face or other such part that one is earth, another water, another fire, they couple each separate sense-organ with a separate element, asserting this one to be air and that other to be fire.
Sensation, then, is confined to the simple or homogeneous parts. But, as might reasonably be expected, the organ of touch, though still homogeneous, is yet the [15] least simple of all the sense-organs. For touch more than any other sense appears to be correlated to several distinct kinds of objects, and to recognize more than one category of contrasts, heat and cold, for instance, dry and wet, and other similar oppositions. Accordingly, the organ which deals with these varied objects is of all the sense-organs the most corporeal, being either the flesh, or the substance which [20] in some animals takes the place of flesh.