(3) Demarcate, as forming higher or more general cla.s.ses, those groups of groups that have important characters in common; and, if possible, on the same principle, form these higher cla.s.ses into cla.s.ses higher still: that is to say, graduate the cla.s.sification upwards.
Whilst in Division the terms "Genus" and "Species" are entirely relative to one another and have no fixed positions in a gradation of cla.s.ses, it has been usual, in Inductive Cla.s.sification, to confine the term "Species" to cla.s.ses regarded as lowest in the scale, to give the term "Genera" to cla.s.ses on the step above, and at each higher step to find some new term such as "Tribe," "Order," "Sub-kingdom," "Kingdom"; as may be seen by turning to any book on Botany or Zoology. If, having fixed our Species, we find them subdivisible, it is usual to call the Sub-species "Varieties."
Suppose an attempt to cla.s.sify by this method the objects in a sitting-room. We see at a glance carpets, mats, curtains, grates, fire-irons, coal-scuttles, chairs, sofas, tables, books, pictures, musical instruments, etc. These may be called "Species." Carpets and mats go together; so do chairs and sofas; so do grates, fire-irons, and coal-scuttles and so on. These greater groups, or higher cla.s.ses, are "Genera." Putting together carpets, mats and curtains as "warmth-fabrics"; chairs, sofas and tables as "supports"; books, pictures and musical instruments as "means of culture"; these groups we may call Orders. Sum up the whole as, from the housewife"s point of view, "furniture." If we then subdivide some of the species, as books into poetry, novels, travels, etc., these Sub-species may be considered "Varieties."
A Cla.s.sification thus made, may be tested by the same rules as those given for testing a Division; but if it does not stand the test, we must not infer that the cla.s.sification is a bad one. If the best possible, it is good, though formally imperfect: whatever faults are found must then be charged upon the "matter," which is traditionally perverse and intractable. If, for example, there is a hammock in the room, it must be cla.s.sed not with the curtains as a warmth-fabric, but with the sofas as a support; and books and pictures may be cla.s.sed as, in a peculiar sense, means of culture, though all the objects in the room may have been modified and a.s.sorted with a view to gratifying and developing good taste.
-- 7. The difficulty of cla.s.sifying natural objects is very great. It is not enough to consider their external appearance: exhaustive knowledge of their internal structure is necessary, and of the functions of every part of their structure. This is a matter of immense research, and has occupied many of the greatest minds for very many years. The following is a tabular outline of the cla.s.sification of the
Animal Kingdom | ------------------- | | SUB-KINGDOM, Vertebrates Invertebrates (10 Sub-kingdom 5) or | Phylum: |------------------------------- | | | | Sauropsida Ichthyopsida | | | | --------- ----------- | | | | | CLa.s.s: Mammalia Birds Reptiles Amphibia Fishes | ------------------------- | | SUB-CLa.s.s: Placental Implacental | | | ------------------- | | | DIVISION: Monodelphia Didelphia Ornithodelphia | --------------------------------------- | | | | | ORDER: Quadrumana Rodentia Carnivora Ungulata Caetacea, etc.
| ---------------------------------- | | | SECTION: Pinnigrada Plantigrada Digitigrada | | | (Seals, etc.) (Bears, etc.) | | -------------------------------------- | | | | | GENUS: Mustelidae Viverridae Hyaaenidae Canidae Felidae | | | (Weasels, etc.) (Civets, etc.) | | --------------------------------------- | | | | | | SPECIES: Lion Tiger Leopard Puma Lynx Cat, etc.
| --------------------- | | | VARIETY: African Syrian Cave-lion (extinct)
As there is not s.p.a.ce enough to tabulate such a cla.s.sification in full, I have developed at each step the most interesting groups: Vertebrates, Mammalia, Monodelphia Carnivora, Digitigrada, Felidae, Lion. Most of the other groups in each grade are also subdivisible, though some of them contain far fewer sub-cla.s.ses than others.
To see the true character of this cla.s.sification, we must consider that it is based chiefly upon knowledge of existing animals. Some extinct animals, known by their fossils, find places in it; for others new places have been made. But it represents, on the whole, a cross-section, or cross-sections of Nature as developing in time; and, in order to give a just view of the relations of animals, it must be seen in the light of other considerations. The older systems of cla.s.sification, and the rules for making them, seem to have a.s.sumed that an actual system of cla.s.ses, or of what Mill calls "Kinds," exists in nature, and that the relations of Kinds in this system are determined by quant.i.ty of resemblance in co-inherent qualities, as the ground of their affinity.
-- 8. Darwin"s doctrine of the origin of species affects the conception of natural cla.s.sification in several ways, (1) If all living things are blood-relations, modified in the course of ages according to their various conditions of life, "affinity" must mean "nearness of common descent"; and it seems irrational to propose a cla.s.sification upon any other basis. We have to consider the Animal (or the Vegetable) Kingdom as a family tree, exhibiting a long line of ancestors, and (descended from them) all sorts of cousins, first, second, third, etc., perhaps once, twice, or oftener "removed." Animals in the relation of first cousins must be cla.s.sed as nearer than second cousins, and so on.
But, if we accept this principle, and are able to trace relationship, it may not lead to the same results as would be reached by simply relying upon the present "quant.i.ty of resemblance," unless we understand this in a very particular way. For the most obvious features of an animal may have been recently acquired; which often happens with those characters that adapt an animal to its habits of life, as the wings of a bat, or the fish-like shape of a dolphin; or as in cases of "mimicry." Some b.u.t.terflies, snakes, etc., have grown to resemble closely, in a superficial way, other b.u.t.terflies and snakes, from which a stricter investigation widely separates them; and this superficial resemblance is probably a recent acquisition, for the sake of protection; the imitated b.u.t.terflies being nauseous, and the imitated snakes poisonous. On the other hand, ancient and important traits of structure may, in some species, have dwindled into inconspicuous survivals or be still found only in the embryo; so that only great knowledge and sagacity can identify them; yet upon ancient traits, though hidden, cla.s.sification depends. The seal seems nearer allied to the porpoise than to the tiger, the shrew nearer to the mouse than to the hedgehog; and the Tasmanian wolf looks more like a true wolf, the Tasmanian devil more like a badger, than like a kangaroo: yet the seal is nearer akin to the tiger, the shrew to the hedgehog, and the Tasmanian flesh-eaters are marsupial, like the kangaroo. To overcome this difficulty we must understand the resemblance upon which cla.s.sification is based to include resemblance of Causation, that is, the fact itself of descent from common ancestors.
For organic beings, all other rules of cla.s.sification are subordinate to one: trace the genealogy of every form.
By this rule we get a definite meaning for the phrase "important or fundamental attribute" as determining organic cla.s.ses; namely, most ancient, or "best serving to indicate community of origin." Grades of cla.s.sification will be determined by such fundamental characters, and may correspond approximately to the more general types (now extinct) from which existing animals have descended.
(2) By the hypothesis of development the fixity of species is discredited. The lowest grade of a cla.s.sification is made up not of well-defined types unchanging from age to age, but of temporary species, often connected by uncertain and indistinct varieties: some of which may, in turn, if the conditions of their existence alter, undergo such changes as to produce new species. Hence the notion that Kinds exist in organic nature must be greatly modified. During a given period of a few thousand years, Kinds may be recognised, because, under such conditions as now prevail in the world, that period of time is insufficient to bring about great changes. But, if it be true that lions, tigers, and leopards have had a common ancestor, from whose type they have gradually diverged, it is plain that their present distinctness results only from the death of intermediate specimens and the destruction of intermediate varieties. Were it possible to restore, by the evidence of fossils, all the ranks of the great processions that have descended from the common ancestor, there would nowhere occur a greater difference than between offspring and parents; and the appearance of Kinds existing in nature, which is so striking in a museum or zoological garden, would entirely vanish.
A cla.s.sification, then, as formerly observed, represents a cross-section of nature as developing in time: could we begin at the beginning and follow this development down the course of time, we should find no cla.s.ses, but an ever-moving, changing, spreading, branching continuum.
It may be represented thus: Suppose an animal (or plant) A, extending over a certain geographical area, subject to different influences and conditions of climate, food, hill and plain, wood and prairie, enemies and rivals, and undergoing modifications here and there in adaptation to the varying conditions of life: then varieties appear. These varieties, diverging more and more, become distinct species (AB, AC, AD, AX). Some of these species, the more widely diffused, again produce varieties; which, in turn become species (ABE, ABF, ADG, ADH). From these, again, ABE, ABFI, ABFJ, AC, ADHK, ADHL, ADHM, the extant species, descend.
A /|\_ / | __ / | _____ ________/ | __ / | AB AC AD AX / | / / | / / | / ABE ABF | ADG ADH / / | /| / / | / | / / | / | ABE ABFI ABFJ AC ADHK ADHL ADHM
If in this age a cla.s.sifier appears, he finds seven living species, which can be grouped into four genera (ABE, ABF, AC, ADH), and these again into three Families (AB, AC, AD), all forming one Order. But the animals which were their ancestors are all extinct. If the fossils of any of them--say AB, ADG and AX--can be found, he has three more species, one more genus (ADG), and one more family (AX). For AC, which has persisted unchanged, and AX, which has become extinct, are both of them Families, each represented by only one species. It seems necessary to treat such ancient types as species on a level with extant forms; but the naturalist draws our attention to their archaic characteristics, and tries to explain their places in the order of evolution and their relationships.
But now suppose that he could find a fossil specimen of every generation (hundreds of thousands of generations), from ABFI, etc., up to A; then, as each generation would only differ from the preceding as offspring from parents, he would be unable at any point to distinguish a species; at most, he would observe a slightly marked variety. ABFI and ABFJ would grow more and more alike, until they became indistinguishable in ABF; ABF and ABE would merge into AB; AB, AC, AD and AX would merge into A. Hence, the appearance of species is due to our taking cross-sections of time, or comparing forms that belong to periods remote from one another (like AX, ADG, and ADHK, or AD, ADH and ADHK), and this appearance of species depends upon the destruction of ancestral intermediate forms.
(3) The hypothesis of development modifies the logical character of cla.s.sification: it no longer consists in a direct induction of co-inherent characters, but is largely a deduction of these from the characters of earlier forms, together with the conditions of variation; in other words, the definition of a species must, with the progress of science, cease to be a mere empirical law of co-inherence and become a derivative law of Causation. But this was already implied in the position that causation is the fundamental principle of the explanation of concrete things; and accordingly, the derivative character of species or kinds extends beyond organic nature.
-- 9. The cla.s.sification of inorganic bodies also depends on causation.
There is the physical cla.s.sification into Solids, Liquids, and Gases.
But these states of matter are dependent on temperature; at different temperatures, the same body may exist in all three states. They cannot therefore be defined as solid, liquid, or gaseous absolutely, but only within certain degrees of temperature, and therefore as dependent upon causation. Similarly, the geological cla.s.sification of rocks, according to relative antiquity (primary, secondary, tertiary, with their subdivisions), and mode of formation (igneous and aqueous), rests upon causation; and so does the chemical cla.s.sification of compound bodies according to the elements that enter into them in definite proportions.
Hence, only the cla.s.sification of the elements themselves (amongst concrete things), at present, depends largely upon empirical Coinherence. If the elements remain irresolvable into anything simpler, the definitions of the co-inherent characters that distinguish them must be reckoned amongst the ultimate Uniformities of Nature. But if a definite theory of their origin both generally and severally, whether out of ether-vortices, or groups of electric corpuscles, or whatnot, shall ever gain acceptance, similarity of genesis or causation will naturally be the leading consideration in cla.s.sifying the chemical elements. To find common principles of causation, therefore, const.i.tutes the verification of every Natural Cla.s.sification. The ultimate explanation of nature is always causation; the Law of Causation is the backbone of the system of Experience.
CHAPTER XXII
NOMENCLATURE, DEFINITION, PREDICABLES
-- 1. Precision of thought needs precision of language for the recording of such thought and for communicating it to others. We can often remember with great vividness persons, things, landscapes, changes and actions of persons or things, without the aid of language (though words are often mixed with such trains of imagery), and by this means may form judgments and inferences in particular cases; but for general notions, judgments and inferences, not merely about this or that man, or thing, but about all men or all kinds of things, we need something besides the few images we can form of them from observation. Even if we possess generic images, say, of "horse" or "cat" (that is, images formed, like composite photographs, by a coalescence of the images of all the horses or cats we have seen, so that their common properties stand out and their differences frustrate and cancel one another), these are useless for precise thought; for the generic image will not correspond with the general appearance of horse or cat, unless we have had proportional experience of all varieties and have been impartially interested in all; and, besides, what we want for general thought is not a generic image of the appearance of things, though it were much more definite and fairly representative than such images ever are, but a general representation of their important characters; which may be connected with internal organs, such as none but an anatomist ever sees. We require a symbol connected with the general character of a thing, or quality, or process, as scientifically determined, whose representative truth may be trusted in ordinary cases, or may be verified whenever doubt arises. Such symbols are for most purposes provided by language; Mathematics and Chemistry have their own symbols.
-- 2. First there should be "a name for every important meaning": (a) A Nomenclature, or system of the names of all cla.s.ses of objects, adapted to the use of each science. Thus, in Geology there are names for cla.s.ses of rocks and strata, in Chemistry for the elements and their compounds, in Zoology and Botany for the varieties and species of animals and plants, their genera, families and orders.
To have such names, however, is not the whole aim in forming a scientific language; it is desirable that they should be systematically significant, and even elegant. Names, like other instruments, ought to be efficient, and the efficiency of names consists in conveying the most meaning with the least effort. In Botany and Zoology this result is obtained by giving to each species a composite name which includes that of the genus to which it belongs. The species of Felidae given in chap.
xvii. -- 7, are called _Felis leo_ (lion), _Felis tigris_ (tiger), _Felis leopardus_ (leopard), _Felis concolor_ (puma), _Felis lyncus_ (European lynx), _Felis catus_ (wild cat). In Chemistry, the nomenclature is extremely efficient. Names of the simpler compounds are formed by combining the names of the elements that enter into them; as Hydrogen Chloride, Hydrogen Sulphide, Carbon Dioxide; and these can be given still more briefly and efficiently in symbols, as HCl, H_{2}S, CO_{2}.
The symbolic letters are usually initials of the names of the elements: as C = Carbon, S = Sulphur; sometimes of the Latin name, when the common name is English, as Fe = Iron. Each letter represents a fixed quant.i.ty of the element for which it stands, viz., the atomic weight. The number written below a symbol on the right-hand side shows how many atoms of the element denoted enter into a molecule of the compound.
(b) A Terminology is next required, in order to describe and define the things that const.i.tute the cla.s.ses designated by the nomenclature, and to describe and explain their actions.
(i) A name for every integral part of an object, as head, limb, vertebra, heart, nerve, tendon; stalk, leaf, corolla, stamen, pistil; plinth, frieze, etc. (ii) A name for every metaphysical part or abstract quality of an object, and for its degrees and modes; as extension, figure, solidity, weight; rough, smooth, elastic, friable; the various colours, red, blue, yellow, in all their shades and combinations and so with sounds, smells, tastes, temperatures. The terms of Geometry are employed to describe the modes of figure, as angular, curved, square, elliptical; and the terms of Arithmetic to express the degrees of weight, elasticity, temperature, pitch of sound. When other means fail, qualities are suggested by the names of things which exhibit them in a salient way; figures by such terms as amphitheatre, bowl-like, pear-shaped, egg-shaped; colours by lias-blue, sky-blue, gentian-blue, peac.o.c.k-blue; and similarly with sounds, smells and tastes. It is also important to express by short terms complex qualities, as harmony, fragrance, organisation, s.e.x, symmetry, stratification.
(iii) In the explanation of Nature we further require suitable names for processes and activities: as deduction, conversion, verification, addition, integration, causation, tendency, momentum, gravitation, aberration, refraction, conduction, affinity, combination, germination, respiration, attention, a.s.sociation, development.
There may sometimes be a difficulty in distinguishing the terms which stand for qualities from those that express activities, since all qualities imply activities: weight, for example, implies gravitation; and the quality heat is also a kind of motion. The distinction aimed at lies between a quality as perceived by means of an effect upon our senses (as weight is resistance to our effort in lifting; heat, a sensation when we approach fire), and that property of a body which is conceived to account for its energy (as gravitation that brings a body to the ground, or physical heat that expands an iron bar or works an engine). The former cla.s.s of words, expressing qualities, are chiefly used in description: the latter cla.s.s, expressing activities, are chiefly needed in explanation. They correspond respectively, like cla.s.sification and explanation, with the static and dynamic aspects of Nature.
The terms of ordinary language fall into the same cla.s.ses as those of science: they stand for things, cla.s.ses of things, parts, or qualities, or activities of things; but they are far less precise in their signification. As long as popular thought is vague its language must be vague; nor is it desirable too strictly to correct the language whilst the thought is incorrigible. Much of the effect of poetry and eloquence depends upon the elasticity and indirect suggestiveness of common terms.
Even in reasoning upon some subjects, it is a mistake to aim at an unattainable precision. It is better to be vaguely right than exactly wrong. In the criticism of manners, of fine art, or of literature, in politics, religion and moral philosophy, what we are anxious to say is often far from clear to ourselves; and it is better to indicate our meaning approximately, or as we feel about it, than to convey a false meaning, or to lose the warmth and colour that are the life of such reflections. It is hard to decide whether more harm has been done by sophists who take a base advantage of the vagueness of common terms, or by honest paralogists (if I may use the word) who begin by deceiving themselves with a plausible definiteness of expression, and go on to propagate their delusions amongst followers eager for systematic insight but ignorant of the limits of its possibility.
-- 3. A Definition is necessary (if possible) for every scientific name.
To define a name is to give a precise statement of its meaning or connotation. The name to be defined is the subject of a proposition, whose predicate is a list of the fundamental qualities common to the things or processes which the subject denotes, and on account of possessing which qualities this name is given to them.
Thus, a curve is a line of which no part is straight. The momentum of a moving body is the product of its ma.s.s and its velocity (these being expressed in numbers of certain units). Nitrogen is a transparent colourless gas, atomic weight 14, specific gravity .9713, not readily combining, etc. A lion is a monodelphian mammal, predatory, walking on its toes, of nocturnal habits, with a short rounded head and muzzle; dental formula: Incisors (3-3)/(3-3), canines (1-1)/(1/1), praemolars (3-3)/(2-2), molars (1-1)/(1-1) = 30; four toes on the hind and five on the fore foot, retractile claws, p.r.i.c.kly tongue, light and muscular in build, about 9-1/2 feet from muzzle to tip of tail, tawny in colour, the males maned, with a tufted tail. If anything answers to this description, it is called a lion; if not, not: for this is the meaning of the name.
For ordinary purposes, it may suffice to give an Incomplete Definition; that is, a list of qualities not exhaustive, but containing enough to identify the things denoted by the given name; as if we say that a lion is "a large tawny beast of prey with a tufted tail." Such purposes may also be served by a Description; which is technically, a proposition mentioning properties sufficient to distinguish the things denoted, but not the properties that enter into the definition; as if nitrogen be indicated as the gas that const.i.tutes 4/5 of the atmosphere.
-- 4. The rules for testing a Definition are: I.--As to its Contents--
(1) It must state the whole connotation of the name to be defined.
(2) It must not include any quality derivative from the connotation.
Such a quality is called a Proprium. A breach of this rule can do no positive harm, but it is a departure from scientific economy. There is no need to state in the definition what can be derived from it; and whatever can be derived by causation, or by mathematical demonstration, should be exhibited in that manner.
(3) It must not mention any circ.u.mstance that is not a part of the connotation, even though it be universally found in the things denoted.
Such a circ.u.mstance, if not derivable from the connotation, is called an Accident. That, for example, the lion at present only inhabits the Old World, is an accident: if a species otherwise like a lion were found in Brazil, it would not be refused the name of lion on the score of locality. Whilst, however, the rules of Logic have forbidden the inclusion of proprium or accident in a definition, in fact the definitions of Natural History often mention such attributes when characteristic. Indeed, definitions of superordinate cla.s.ses--Families and Orders--not infrequently give qualities as generally found in the subordinate cla.s.ses, and at the same time mention exceptional cases in which they do not occur.
II.--As to its Expression--
(4) A Definition must not include the very term to be defined, nor any cognate. In defining "lion" we must not repeat "lion," nor use "leonine"; it would elucidate nothing.
(5) It must not be put in vague language.
(6) It must not be in a negative form, if a positive form be obtainable.
We must not be content to say that a lion is "no vegetarian," or "no lover of daylight." To define a curve as a line "always changing its direction" may be better than as "in no part straight."
-- 5. The process of determining a Definition is inseparable from cla.s.sification. We saw that cla.s.sification consists in distributing things into groups according to their likenesses and differences, regarding as a cla.s.s those individuals which have most qualities in common. In doing so we must, of course, recognise the common qualities or points of likeness; and to enumerate these is to define the name of the cla.s.s. If we discover the qualities upon which a cla.s.s is based by direct observation and induction, by the same method we discover the definition of its name.