Various Works

  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.

  2

  Some writers propose to reach the definitions of the ultimate

  forms of animal life by bipartite division. But this method is often

  difficult, and often impracticable.

  Sometimes the final differentia of the subdivision is sufficient

  by itself, and the antecedent differentiae are mere surplusage. Thus

  in the series Footed, Two-footed, Cleft-footed, the last term is

  all-expressive by itself, and to append the higher terms is only an

  idle iteration. Again it is not permissible to break up a natural

  group, Birds for instance, by putting its members under different

  bifurcations, as is done in the published dichotomies, where some

  birds are ranked with animals of the water, and others placed in a

  different class. The group Birds and the group Fishes happen to be

  named, while other natural groups have no popular names; for instance,

  the groups that we may call Sanguineous and Bloodless are not known

  popularly by any designations. If such natural groups are not to be

  broken up, the method of Dichotomy cannot be employed, for it

  necessarily involves such breaking up and dislocation. The group of

  the Many-footed, for instance, would, under this method, have to be

  dismembered, and some of its kinds distributed among land animals,

  others among water animals.

  3

  Again, privative terms inevitably form one branch of dichotomous

  division, as we see in the proposed dichotomies. But privative terms

  in their character of privatives admit of no subdivision. For there

  can be no specific forms of a negation, of Featherless for instance or

  of Footless, as there are of Feathered and of Footed. Yet a generic

  differentia must be subdivisible; for otherwise what is there that

  makes it generic rather than specific? There are to be found

  generic, that is specifically subdivisible, differentiae; Feathered

  for instance and Footed. For feathers are divisible into Barbed and

  Unbarbed, and feet into Manycleft, and Twocleft, like those of animals

  with bifid hoofs, and Uncleft or Undivided, like those of animals with

  solid hoofs. Now even with differentiae capable of this specific

  subdivision it is difficult enough so to make the classification, as

  that each animal shall be comprehended in some one subdivision and

  in not more than one; but far more difficult, nay impossible, is it to

  do this, if we start with a dichotomy into two contradictories.

  (Suppose for instance we start with the two contradictories, Feathered

  and Unfeathered; we shall find that the ant, the glow-worm, and some

  other animals fall under both divisions.) For each differentia must be

  presented by some species. There must be some species, therefore,

  under the privative heading. Now specifically distinct animals

  cannot present in their essence a common undifferentiated element, but

  any apparently common element must really be differentiated. (Bird and

  Man for instance are both Two-footed, but their two-footedness is

  diverse and differentiated. So any two sanguineous groups must have

  some difference in their blood, if their blood is part of their

  essence.) From this it follows that a privative term, being

  insusceptible of differentiation, cannot be a generic differentia;

  for, if it were, there would be a common undifferentiated element in

  two different groups.

  Again, if the species are ultimate indivisible groups, that is,

  are groups with indivisible differentiae, and if no differentia be

  common to several groups, the number of differentiae must be equal

  to the number of species. If a differentia though not divisible

  could yet be common to several groups, then it is plain that in virtue

  of that common differentia specifically distinct animals would fall

  into the same division. It is necessary then, if the differentiae,

  under which are ranged all the ultimate and indivisible groups, are

  specific characters, that none of them shall be common; for otherwise,

  as already said, specifically distinct animals will come into one

  and the same division. But this would violate one of the requisite

  conditions, which are as follows. No ultimate group must be included

  in more than a single division; different groups must not be

  included in the same division; and every group must be found in some

  division. It is plain then that we cannot get at the ultimate specific

  forms of the animal, or any other, kingdom by bifurcate division. If

  we could, the number of ultimate differentiae would equal the number

  of ultimate animal forms. For assum
e an order of beings whose prime

  differentiae are White and Black. Each of these branches will

  bifurcate, and their branches again, and so on till we reach the

  ultimate differentiae, whose number will be four or some other power

  of two, and will also be the number of the ultimate species

  comprehended in the order.

  (A species is constituted by the combination differentia and matter.

  For no part of an animal is purely material or purely immaterial;

  nor can a body, independently of its condition, constitute an animal

  or any of its parts, as has repeatedly been observed.)

  Further, the differentiae must be elements of the essence, and not

  merely essential attributes. Thus if Figure is the term to be divided,

  it must not be divided into figures whose angles are equal to two

  right angles, and figures whose angles are together greater than two

  right angles. For it is only an attribute of a triangle and not part

  of its essence that its angles are equal to two right angles.

  Again, the bifurcations must be opposites, like White and Black,

  Straight and Bent; and if we characterize one branch by either term,

  we must characterize the other by its opposite, and not, for

  example, characterize one branch by a colour, the other by a mode of

  progression, swimming for instance.

  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 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 members that are wild. Such, for example, is the

  case with Men, Horses, Oxen, Dogs in India, Pigs, Goats, Sheep; groups

  which, if double, ought to have what they have not, namely,

  different appellations; and which, if single, prove that Wildness

  and Tameness do not amount to specific differences. And whatever

  single element we take as a basis of division the same difficulty will

  occur.

  The method then that we must adopt is to attempt to recognize the

  natural groups, following the indications 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 divisions or contrary groups under the

  same division), or it only furnishes a single ultimate differentia for

  each species, which either alone or with its series of antecedents has

  to constitute the ultimate species.

  If, again, a new differential character be introduced at any stage

  into the division, the necessary result is that the continuity of

  the division becomes merely a unity and continuity of agglomeration,

  like the unity and continuity of a series of sentences coupled

  together by conjunctive particles. For instance, suppose we have the

  bifurcation Feathered and Featherless, 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 foreign to the series at the end of

  which they are introduced.

  As we said then, we must define at the outset by multiplicity of

  differentiae. 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 with its antecedents,

  shall express the whole essence of a species. (In saying a single

  differentia by itself I mean such an isolated differentia as

  Cleft-footed; in saying a single differentia with antecedent I mean,

  to give an instance, Manycleft-footed preceded by Cleft-footed. The

  very continuity of a series of successive differentiae in a division

  is intended to show that it is their combination that expresses the

  character of the resulting unit, or ultimate group. But one is

  misled by the usages of language into imagining that it is merely

  the final term of the series, Manycleft-footed for instance, that

  constitutes the whole differentia, and that the antecedent terms,

  Footed, Cleft-footed, are superfluous. 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, that is, to the

  species.) No single differentia, I repeat, either by itself or with

  its antecedents, can possibly express the essence of a species.

  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 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 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 not identical but analogous are

  separated. For instance, bird differs from bird by gradation, or by

  excess and defect; some birds have long feathers, others short ones,

  but all are feathered. Bird and Fish are more remote and only agree in

  having analogous organs; for what in the bird is feather, in the

  fish is scale. Such analogies can scarcely, however, serve universally

  as indications for the formation of groups, for almost all animals

  present analogies in their corresponding parts.

  The individuals comprised within a species, such as Socrates and

  Coriscus, are the real existences; but inasmuch as these individuals

  possess one common specific form, it will suffice to state the

  universal attributes of the species, that is, the attributes common to

  all its individuals, once for all, as otherwise there will be

  endless reiteration, as has already been pointed out.

/>   But as regards the larger groups-such as Birds-which comprehend many

  species, there may be a question. For on the one hand it may be

  urged that as the ultimate species represent the real existences, it

  will be well, if practicable, to examine these ultimate species

  separately, just as we examine the species Man separately; to examine,

  that is, not the whole class Birds collectively, but the Ostrich,

  the Crane, and the other indivisible groups or species belonging to

  the class.

  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 the universal attributes of

  the groups that have a common nature and contain closely allied

  subordinate forms, whether they are groups recognized by a true

  instinct of mankind, such as Birds and Fishes, or groups not popularly

  known by a common appellation, but withal 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-stands apart from

  others, and does not constitute with them a larger natural group.

  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 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.

  We have now touched upon the canons for criticizing the method of

  natural science, and have considered what is the most systematic and