Moreover, it seems more apt than the other to explain certain facts of current experience. It is a matter of common observation that time seems long to us, under two contrary conditions: (1) when it is very long; (2) when it is very empty. Here we have an apparent psychological contradiction. The two cases, however, are equally explained by the quantity of the states of consciousness: the first is filled with events, the second, with efforts. After three or four days of a journey fertile in incident, one seems to have left home a long time, because (in comparison with three or four days of ordinary life) the quantity of adventures held in mind, each implying a quantum of duration, appears to us in sum as an enormous duration. On the other hand, to the prisoner incarcerated in a cell, to the traveller at a deserted station waiting for a train; briefly, to all who are in the state known by the name of expectant attention, time seems to be of immeasurable extension. This is because there is a constant expenditure of effort, a tension incessantly renewed, incessantly frustrated; consciousness is nearly void of representations, while it is filled with acts of attention constantly repeated. This instance of time prolonged, while apparently empty, is difficult to explain, if only the intellectual elements are taken into consideration, omitting the consciousness of motor states. It should be noticed that “full” time seems longer in the past; “empty” time, in the present and immediate past; perhaps because the former rests principally upon intellectual memory, which is stable; the latter, upon motor memory, which is vague and fragile.
SECTION IV. CONCEPT OF CAUSE.
The idea of cause has for centuries been the subject of so many speculations, that our first care must be to confine ourselves scrupulously to our subject, i. e., to retrace its evolution simply, marking the principal phases of its development in the individual and the species, while as far as possible eliminating whatever lies outside this one question.
It has been remarked that the word cause signifies sometimes an antecedent, sometimes a process, sometimes antecedent, process, and effect produced, taken all three together.[121] This last sense alone is complete. For, if the primitive, popular conception tends to restrict the cause to the antecedent, to that which acts, a little reflexion will show us that the cause is only determined as such by its effect, that the two terms are correlative, the one not existing without the other. Finally, with more profound reflexion, the process itself, the transition, the passage, the nexus between antecedent and consequent, appears as the vital point, the proprium quid of causality. As psychical fact, as state of consciousness, therefore, this notion is complex, and among the elements which compose it, now one and now the other, according to the epoch, has been considered the most important.
In what follows, we shall have to consider: I. the origin of the idea of cause in experience; II. its generalisation, and passage from the individual subjective, to the objective form; III. its transformation as resulting from the work performed in the various sciences, its scission into two fundamental ideas: on the one hand, that of force, energy, active and effective power, cause in the true sense (vera causa), which tends more and more to become a postulate, an x, a metaphysical residuum; on the other, that of a constant and invariable succession, a fixed relation, which becomes the scientific form of the concept of cause, equivalent in all respects to the concept of law.
I. Every one seems agreed, fundamentally at least, upon the empirical origin of the idea of cause. It is of internal, subjective origin; suggested to us by our motor activity. A being who was hypothetically perfectly passive, while seeing or feeling constant external sequences, would have no idea of causality. It would be superfluous to show, by multiplying our quotations, that spiritualists like Maine de Biran, empiricists like Mill, critics like Renouvier, all the schools in short, with varying formulæ, agree upon this point. At the same time it must not be overlooked that some writers attribute an exclusive privilege to the “will,” maintaining it to be the type of causality; whereas the assertion that “our own voluntary action is the exclusive source whence this idea is derived” is unjustifiable. If, with some authors, the word “will” is used in a large and vague sense, as designating all mental activity that is translated by movements, no objection can be raised. But if it be used in the proper, restricted sense, as meaning a fully conscious, deliberate act, resulting from motive, the statement cannot be accepted.[122] Volition is a state that makes its appearance somewhat tardily. It is preceded by a period of appetites, of needs, instincts, desires, passions; and all these facts of internal activity, translated into movements; are as apt as the “will” to engender the empirical notion of cause, i. e., transitive action, i. e., change produced: they have moreover the advantage of being anterior in chronological order.
Contemporary psychology has studied the rôle of movements, far more than any of its predecessors. It attributes to them a capital importance; it shows that motor elements are included in every intellectual state without exception, in percepts, in images, and even in concepts. Hence it feels no repugnance in accepting the common thesis. We must however remember that the psychology of motion is centred in the consciousness of muscular effort, which moreover represents the type of primitive causality. The nature of this sense of effort has given rise to long and animated debate. For some, it is of central origin: It is anterior to, or at least concomitant with, the movement produced; it goes from within outwards—it is efferent. For others, it is of peripheral origin, posterior to the movement produced; it goes from without, inwards—is afferent. It is an aggregate of the sensations coming from the articulations, tendons, muscles, from the rhythm of respiration, etc.: so that the sense of effort is no more than the consciousness of energy that has been expended, of movements that have been effectuated: it is a resultant. This second theory, without so far being decisively and incontestably established, is daily gaining more adherents, and remains the most probable. So that, since consciousness of effort is essentially that of effect produced, it follows that in considering the act as the source of the idea of cause, we know much less of antecedent than of consequent. Yet this consciousness of effort produced is not the whole, whatever people may say, of what is in the primitive conception of a proper, personal causality. Something more remains: this is the confused idea, illusory or not, of a creation that proceeds from us. We shall return to this point.
To conclude: at the outset, the two terms antecedent and consequent, form almost the exclusive elements in the notion of cause. At any rate, they preponderate in consciousness, to the exclusion of the third, relation. The idea of a constant invariable sequence, which was, later on, to be the intrinsic mark of the causal process, cannot yet be distinguished.
II. The idea of cause—at first strictly individual—soon commences its movement of extension.
1. During the first period, this extension is the work of the imagination, rather than of generalisation properly so called. By an instinctive tendency, well-known, though not explained, man concludes for intentions, a will, and a causality analogous to his own, in the medium that acts and reacts around him: his fellows, all living things, and whatever else by their movements simulate life (clouds, rivers, etc.). This is the period of primitive fetishism that is fixed in mythologies and languages. It may actually be observed in children, in savage races, in brutes (as in the dog that bites the stone by which it is hit), even in rational man, when—becoming again for the moment a creature of instinct—he falls into a passion at the table that has hurt him.
This period corresponds fairly well with that of generic images, because the idea of cause thus generalised results from gross, external, partial, accidental resemblances, which the mind perceives almost passively. It cannot be doubted that the higher brutes have a generic image of causality; i. e., they are capable—given an antecedent—of invariably representing to themselves the consequence. This mental state, which has been termed “empirical consecution,” and which is not infrequent even among men who may never rise beyond it, resolves itself into a permanent association of ideas, the result of repetition and of habit.[123]
All this, however, is merely an external conception of causality, of its form, and not its nature; it is an outside view, an approximation. The proper characteristic of this period is that it remains subjective, anthropomorphic, representing cause as an intentional activity, which produces movements only in view of an end.
2. The second period begins with philosophic reflection, and proceeds by the slow constitution of the sciences. Its development may thus be summarised: little by little it deprives the notion of cause of its subjective, human character, without however completely attaining this ideal end; it reduces the essentials of the concept to a fixed, constant, and invariable relation between a determined antecedent and consequent; hence it sees in cause and effect only the two moments, or aspects of one and the same process, which is fundamentally the affirmation of an identity.
Here imagination recedes, to make way for abstraction and generalisation,—for abstraction since it is less a question of terms than of a certain relation between the terms, for generalisation because the natural tendency of the mind is to extend causality to the whole of experience.
It must, however, be remarked that the transition from particular cases to generalisation, and finally to the universalisation of the concept of cause, in a strict sense, has only been effected little by little. An opinion that has gained much credit, on the authority of the apriorists, is that every man has an intuitive, innate idea of the law of causality, as universal. This thesis is equivocal. If it means that all change suggests to every normal man who witnesses it an invincible belief in a known or unknown agent of its production, then the assertion is incontestable: but this, as we have seen, is only the popular, practical, and external notion of causality. If the true concept (that of the solidly constituted sciences), which is reducible to an inflexible, invariable determination, is implied, then it is a fallacy to pretend that the human mind acquired it at the outset. The belief in a universal law of causality is no gratuitous gift of nature: it is a conquest. The fallacy persists, because for at least three centuries this idea has been propagated by the writings of philosophers and scientists who have made it familiar enough. None the less, it is a late conception, unknown to the great mass of the human species. Scientific research began by establishing laws, (i. e., invariable relations of cause and effect) between certain groups of phenomena, began by establishing a law of causality that was valid for these and these only; and the transfer of this law to all that is known and unknown has only been effected little by little, and is even yet incomplete. In a word, the law of universal causality is the generalisation of particular laws, and remains a postulate.
In support of the above (without entering into historical detail) we may note the existence in human consciousness of two ideas, which from time to time, each after its own fashion, give check to the universality of the principle. Although, from the development of scientific thought, their influence has been a decreasing factor, they are still very active. These two ideas are those of miracle and chance.
Miracle, taking this word not in the restricted, religious sense, but in its etymological acceptance (mirari), is a rare and unexpected event, produced extrinsically to, or against, the ordinary course of events. The miracle gives no denial to cause, in the popular sense, because it assumes an antecedent: God, an unknown power. It does deny it, in the scientific sense, since it is an abrogation of determinism among phenomena. Miracle is cause without law. Now, for a long period, no belief could have appeared more natural. In the physical world, the appearance of a comet, eclipses, and many other things were regarded as prodigies and warnings. Many races are still imbued with weird fancies on this subject (monsters that would swallow up the sun or moon, etc.), and even among civilised men these phenomena produce in many minds a certain uneasiness. In the biological world, this belief has been much more tenacious: enlightened spirits in the seventeenth century still admitted the errores or lusus naturæ, held the birth of monstrosities to be a bad augury, and so on. In the psychological world it has been even worse. Not to speak of the widely-spread (and not yet extinct) prejudices of antiquity as to prophetic dreams, auguries of the future; of the mystery which so long surrounded natural or induced somnambulism, and analogous contemporary speculations on the occult sciences; of those who regard liberty as an absolute beginning, etc.: there is, even in the limited circle of scientific psychology, so little well-determined relation between cause and effect, that the partisans of contingency may comfortably imagine anything. Useless to insist upon sociology. We need only recall the fact that Utopians abound who, while rejecting miracle in the religious order, admit it freely in the social; believing all to be possible, and reconstructing human society from top to bottom according to their dreams. If, finally, we consider that this very dry and incomplete enumeration covers millions of cases, past and present, we must recognise that the human mind in its spontaneous and self-governed progress, experiences no reluctance to admit causes without law.
The idea of chance is more obscure. We might almost say that, for the majority of people who make no attempt to clear it up, it is an event that supposes neither cause nor law; it is sheer indetermination, a cast of the die arriving no one knows how, by means of no one knows what. It is very evident that chance excludes neither cause nor law, but evident to those alone who have reflected upon its nature, and have analysed the notion. To others, it is a mysterious, impenetrable entity, a Tyche whose acts cannot be foreseen. Hume says that “chance is only our ignorance of true causes.” Cournot rightly observes that this is incorrect, that chance involves something real and positive: the conjunction, the crossing of several sequences of cause and effect, which are independent of one another by origin, and not naturally intended to exert any reciprocal influence. Thus one series of causes and effects lead a traveller to take a particular train: on the other hand a totally distinct set produces at a given place or time an accident which kills the man.[124] There is, in short, in chance, no contravention of the laws of universal mechanism. Why then does it seem to the vulgar mind to be an exception, indeterminate by nature? First, because the problem set by the unexpected is insufficiently analysed; but also in my opinion, because the primitive idea of cause is nearly always that of a single antecedent, whereas here the unique antecedent is not present, and cannot be discovered. The conception of a complex causation, constituted by a sum of concurrent conditions, of equal necessity, is the fruit of advanced reflexion.
Accordingly, while the man who is formed by scientific discipline refuses when confronted with these so-called prodigious or fortuitous facts, to concede that they are exceptions to the law of universal causality, others are quite ready to admit that the wall that surrounds phenomena may give way at certain points, with resulting breaches.
From the point of view of pure psychology, it is impossible not to affirm that the idea of universal causality, of uniformity in the course of nature, of rigorous determinism (and other analogous formulæ), is acquired—superposed. Whether this notion be applicable to the whole of experience, although experience is not yet exhausted, or whether it is simply a guide to research, a stratagem for introducing order into things, is a question which psychology has no capacity for discussing, still less power to resolve.
III. We return to the work of transformation, which, starting with the notion of cause as it is given in experience—i. e., a force, a power, that acts and produces—culminates finally in its last term, the law of causality.
Just as the plurality of objects perceived in nature, forms the material of the concept of number; as the diverse durations present in our consciousness are the material of the concept of time; so our consciousness of acting, of modifying our self and our environment (a power which we attribute freely to everything that surrounds us) is the prime material of the concept of cause. But in order that this concept may be constituted as such—fixed and determined—a work of abstraction is needed to isolate and bring into relief its distinctive, essential characteristic from among all the different elements that compose the primitive and complex notion of empirical cause (antecedent, consequent, action or reaction, change, transformation, etc.). This distinctive characteristic is an invariable relation of sequence (the conditions being supposed the same); and the establishment of it has been, almost exclusively, the result of scientific research.
A history of the secular fluctuations in the idea of cause, as affected by the various philosophical theories and changes of method in the sciences, would be the best review of the phases of its evolution. Impossible here to attempt such a task. We may only note the two extreme points: the speculations of antiquity, and the contemporaneous aspect of the question.[125]
The ancient philosophers who (at least during the great eras) were at once metaphysicians and scientists, constructed systems of cosmogony and assumed “first causes,” which were conceived either as forces, principles of action, motive elements of nature (water, air, fire, atoms), or as rational types (numbers, ideas). On the other hand they invented mathematics, and laid the foundations of astronomy and physics. Now, as regards causality, these essays at the scientific investigation of nature involved consequences which were not plainly disclosed until a much later period. They exacted another position,—a passage from subjective to objective: whether in relation to the fall of bodies, or to a law of hydrostatics (such as that to which Archimedes gave his name), any one who studies the physical world necessarily sees its changes from without. He considers cause no longer as an internal factor revealed by consciousness, but as a sequence given by the senses. Antecedents, consequents, invariable succession, are for him the only useful data. Conditions equal cause; and the important determination is that not of an operating entity, but of a constant relation. This—the only scientific conception of cause—it is which is covered by Stuart Mill’s definition: “Cause is the sum of the positive and negative conditions, which, when given, are followed by an invariable consequent.”
This external aspect, old as science itself, was big with consequences that have only been clearly revealed in our own day, and which may be summed up in a word as identity of cause and effect. There is no separation between the two; the antecedent is not one thing and the consequent another; they are two manifestations, different in time, of a fundamental unity. It has rightly been observed that the mechanical theory of the universe (correlation of forces, conservation and transformation of energy, etc.) is the contemporaneous form of the concept of natural causality. Expressed from earliest antiquity in the form of a metaphysical anticipation (ex nihilo nihil), it enters in the seventeenth century upon its scientific phase, and is completed in our own day. The physicists who have established it upon experience and by calculation, saw plainly the consequences it involved. To cite only one instance, R. Mayer in his Mechanik der Wärme says, “If the cause c produces the effect e, then c = e; if e is the cause of another effect f, then e = f, and so on. Since c becomes e, e = f, etc., we must consider these magnitudes as the different phenomenal forms of one and the same object. Just as the first property of cause is its indestructibility, so the second property is convertibility, i. e., capacity for assuming different forms. And this capacity must not be regarded as a metamorphosis; each cause is invariable, but the combination of its relations is variable. There is quantitative indestructibility and qualitative convertibility.”
It must not be forgotten that the general principles of thermodynamics—the latest form of the concept of natural causality—are not absolute, but are proposed as ideal. We know, e. g., that heat can never give rise again to all the work from which it was produced, that no physical event is exactly reversible, i. e. it cannot be reproduced identically at the opposite end of the process, because in its first appearance it had to overcome resistance, and thus lost part of its energy. All this, however, is outside our scope. As much as the doctrine of the conservation of energy is valid, so much is the actual concept of natural causality worth. We merely undertook to follow the evolution of this concept down to the present day, to point out its transformations, without in any way prejudging the future, or still less attributing to it any absolute value.[126]
What now becomes of the idea of causality taken in the other sense, no longer as an invariable relation of antecedent to consequent, but as a thing that acts, creates, modifies, or persists under all transformations and clothes all masks? The scientific method, as soon as it penetrates into any order of phenomena, tends to exclude cause, to reduce it to the strictest limits, to make the least possible use of it. Cause then becomes the synonym of force. But physical science defines force only by its effects:—movement, or work done. So, too, the biologist rejects the notion of “vital force”; non-metaphysical psychology will have none of the “faculties,” intervention of “the soul,” and the like. Is the notion thus discarded, totally suppressed? Nay,—for even in mechanics and physics it cannot be entirely eliminated. It is there as a postulate, a residuum, an unknown factor covering lacunæ. Yet, do what we will, force or energy, in order to be more than an empty word and to become intelligible, can only be represented and imagined under the form of the muscular effort whence it originates, and which is its type; and despite all the elaborations to which it is submitted in order to rid it of its anthropomorphical character, and dehumanise it, it remains rather a fact of internal experience than a concept. Is it destined to undergo other transformations, by reason of more profound apprehension, or some new aspect of the problem? Is there—along with mechanical causality and rigorous determinism—room for any other mode of causality, proper to psychology, to linguistics, to history, in short to the positive sciences of the mind, as is maintained by Wundt and others? The secret remains for the future.
The natural tendency of the mind (which is but one aspect of the instinct of conservation) to seek and investigate in face of the unknown and unexpected, its clear or confused need of explanation for better or worse, at the outset concluded for an acting entity. The idea still survives under a naïve or transcendental form; it reappears in every unexplained contingency, whether in regard to the first origin of things, or (for the partisans of liberty) to freedom of action. In this sense, “causality is an altar to the Unknown God, an empty pedestal that awaits its statue.”[127]
In its other sense, which is widely different and even contrary, which has been slowly fixed, and more slowly extended to the whole of experience, cause is a true concept: the resultant namely of abstraction, summarised in the characters exclusively proper to it. Under this form it is equivalent to the concept of law.
SECTION V. CONCEPT OF LAW.
Our general ideas, from those immediately bordering on the concrete to those which attain pure symbolism, constitute a hierarchy of ever-increasing simplicity. What value must be assigned to this thinking by concepts, in proportion as it ascends higher in the scale? We are all familiar with the debates upon this question, bearing, as it does, fundamentally upon the objective value of abstraction and generalisation. Psychology, as the science of facts, is able to ignore this point, since it is concerned only with the nature of the two intellectual processes, their variations, and adaptations to multiple cases. Still, it is reasonable enough that it should assume a position, at any rate provisionally, and for convenience of discussion.
To recall only the two extreme opinions: On the one side we have those who maintain that the particular alone exists—for event or individual—that our general ideas are but a means of maintaining order, while they teach us nothing as to the nature of things. They are comparable to a catalogue, or to the card-index of a library which are an easy indicator to the millions of books, leaving us totally ignorant as to their contents and value. Hence, the higher we ascend, the farther we penetrate into the region of the fictitious and the vacant.
On the other hand, there are those who assert that nature has general and fixed characteristics; in discovering them, we penetrate into the essence of things. Events and individuals have but a borrowed existence; under their fleeting appearances, we must seek the enduring; and thus, the greater the generalisation, the higher we rise in reality and in dignity.
The psychologist can only take up the position of relativity. To him, general ideas are approximations: they have an objective value, but it is provisional and momentary, dependent on the variability of phenomena and on the state of our knowledge.
On the one hand, the similarities that are the substrata of generalisation are not fictitious. Since, moreover, knowledge of the laws of nature has a practical value, by enabling us to act upon things, and since we fail, in ignorance of them,—we are fain, objections notwithstanding, to attribute to them at least a certain measure of objective value.
On the other, if there is evolution in nature, there must also be evolution in our ideas, and the pretension to laws or types that are fixed unalterably, becomes chimerical. There is no longer the sharp distinction, as formerly admitted, between “essential” and “accidental,” i. e., permanent and variable characters. The Primary epoch of our globe may have obeyed laws which no longer hold for our Quaternary age: all changes in the course of development. We shall return to this point in the concluding section.
Without insisting further upon a debate that is of secondary interest for the psychologist, we may remark that three principal periods can be distinguished in the development of the Concept of Law: viz., the periods of generic images, of concrete or empirical laws, and of theoretical or ideal laws.
It is useless to study the first phase in detail, since it interests us only as an embryonic form, a germ, or essay. It consists in the mechanical conception of regularity for a very restricted number of events. Resulting from the constant or frequent repetition of certain cycles (the course of the sun, moon, seasons, etc.) it is organised in the mind by a process of semi-passive assimilation, that of generic images. Many men have had, and still have, only this shadow, this simulacrum of law, resting upon pure association, upon practical habit, upon the unreflecting expectation of an often-perceived recurrence. Humble as it is, this notion was nevertheless useful in the education of humanity, for it checked the exuberant tendency of the imagination to people the world with capricious causes, obedient to no law. It prevented the establishment of a rule of universal contingency; it was the first affirmation of a faith in regular order. The progress of reflexion, and methodical research, have done the rest.
We owe to Wundt (Philosophische Studien, 1886, III., p. 195 et seq.) an observation of great interest to any one concerned in the development of the idea of law. To-day this word is current in all the sciences; indeed its most rigorous acceptance is in mathematics and chemical physics. This was not always the case. In antiquity, the word was employed almost exclusively in a social, juristic, moral sense. The concept of natural law, regarded as a sort of order, a police-force, was only very slowly formed and established. Copernicus and Kepler employed the word “hypothesis.” Galileo calls the fundamental laws of nature “axioms,” and those derived from them “theorems,” following the terminology of the mathematicians. Descartes begins his Philosophy of Nature by laying down certain Regulæ sive leges naturales. Newton says: Axiomata sive leges motus. The extension of the word law is due apparently to the need of establishing a clear distinction between the purely abstract axioms of mathematics, and the principles to which we attribute an objective value, an existence in nature. Montesquieu’s celebrated definition, “Laws are the necessary relations derived from the nature of things,” exhibits this concept in its highest degree of generalisation. We may note, in passing, that in the enquiry referred to above (ch. IV.), nearly all the answers indicate that images of the social juristic order were evoked, although the scientific acceptance of the word was perfectly familiar to a large number of the subjects: showing that the primitive signification preponderates in the vulgar conscience.
In another article, entitled Wer ist der Gesetzgeber der Naturgesetze? (loc. cit., pp. 493 et seq.), the same author maintains an opinion, which, notwithstanding its paradoxical appearance, seems to me perfectly valid. Descartes called the laws of nature “rules,” inasmuch as they explain phenomena to us; “laws,” inasmuch as God constituted them ab initio as properties of matter. At a later period, nature takes the place of God, which is still the survival of a pantheistic conception of the world. Still later, the preponderating tendency is to call laws by the names of their inventors: Mariotte, Gay-Lussac, Dulong and Petit, Avogadro, Ohm, Weber, etc. “In the seventeenth century it was God who established the laws of nature; in the eighteenth it was Nature herself; in the nineteenth it is the affair of the scientists.” This thesis agrees with what was said above, of the approximate character of laws, of the mixture of objective and subjective elements that obtain in their formulæ, and it is no paradox to assert that the state of mind of a Mariotte, a Gay-Lussac, a Weber, etc., when they discover their law, represents this approximation at a given moment.
I. Empirical laws correspond, broadly speaking, with the intermediate forms of abstraction and of generalisation. They consist in the reduction of a large number of facts to a single formula, but without any rational explanation. In the course of events we discover a constant relation of co-existence or of succession between two or several facts; we mentally detach this regular relation from the total which includes it, and extend it to other cases. Constancy is not even necessary for empirical laws, frequency suffices: at least one often has to be content with it. These laws abound in the half-sciences, and in embryo science: they are useful, they give order and simplification.
Their first characteristic is that they are identical with fact. Laws and facts are only two aspects of the same thing. To pass from facts to their empirical law, is merely replacing simple and homogeneous cognition by abstraction, multiple and heterogeneous cognition by perception. Hence the empirical law is rightly compared to a general fact, and it is legitimate in psychology to say the law of association or the general fact of association. On the other hand (in virtue of the natural tendency to anthropomorphism) vulgarisms such as “laws govern facts,” and the like, encourage in many minds the illusion of an ideal world of law superposed upon the world of facts, external to experience, and acting upon it like a government.
A second characteristic, which though frequent is not universal, is complexity. Necessarily objective, since it is a simple notation of observed facts, the empirical law does not always succeed in embracing the results of abstraction in one short and simple formula. Sometimes it does so; sometimes it is confronted with a multiplicity that cannot be reduced to a single proportion; in many cases it has to distribute itself, and resignedly to employ a long formula. Ex.: in physiology, Pflüger’s law (or the laws of reflexes), in linguistics, the laws of Grimm, etc. Here there is a summary description, reduced to the principal facts. It often has to cover a great number of details, as in Listing’s law (of the rotation of the ocular globe). Plenty of examples are to be found in the sciences that are in process of formation, and ill-constituted: psychology,[128] ethics, sociology, etc. Empirical law could only be further simplified by changing its nature, namely by transforming it into theoretical law.
Empirical law is thus the type of law that is immanent, contained in the facts, invoking their representation directly and indirectly by means of intermediate abstraction, involving ascending degrees of abstraction, that, at their highest level, bring it insensibly very near to ideal law.
II. Theoretical, or ideal, law corresponds with the higher forms of abstraction. It exhibits increasingly approximative constructions of the mind, in proportion as these ascend, and are farther removed from experience. Empirical laws are the material whence they are derived, and the transformation is accomplished at the moment, and in the degree, in which description gives place to explanation. To minds accustomed to the discipline of the strict sciences, this conception of law alone is valid, and they are prone to treat with disdain or defiance the formulæ that are a simple summing-up of the results of experience, judging them unworthy of the name of laws. To the psychologist, the position is quite other: empirical concept and theoretical concept are two forms, two aspects of the same intellectual process: there is no constitutional difference between them. Nevertheless, in its higher form, the concept of law has its proper and special characteristics which must be noted.
1. Simplicity, as contrasted with the complexity of empirical laws; this is the necessary corollary of the operation that gives rise to it, since it is an abstraction of abstractions, the final result of a long series of eliminations. Compare with the long, vague, entangled formulæ, charged with details, of which examples were given above, the enunciation of the higher laws, which are usually short and invariably precise. And, it may be added, invariably lucid, at least to the scientist who is in the habit of dealing with them, because he knows exactly what they cover. In this connexion a saying of D’Alembert deserves to be recalled and considered, because it discloses, better than any commentary, the psychology of abstract minds: “The most abstract notions, such as the majority of mankind regard as the most inaccessible, are often those which carry with them the greatest elucidating power: our ideas seem to be blotted out by obscurity in proportion as, in any object, we examine into its sensible properties.”
2. Quantitative determination. The higher laws alone can assume a numerical form, and it is a truism to say that the perfection of any science is measured by the quantity of mathematics which it involves. Not that mathematical formulæ imply or confer any magical virtue, but they are the sign of reduction to clear and simple relations, and are frequently an instrument of further progress. It is true that in the domain of empirical law, there are many processes which attempt to imitate quantitative determination: graphic records, curves, statistics, percentages, etc. Yet these are often a very poor substitute for the equation, or worse—for they offer an illusory preciseness, and are fallacious.
3. It is well to insist upon the ideal character of these laws, because one is apt to forget that, in virtue of their very abstraction, they can be approximate only; and can but be applied, and reduced from theory to practice, by means of rectifications and additions. It has been said that “physical laws are general truths that are invariably more or less falsified for each particular case.” All scientific men, and there are many, who have reflected on the subject, bring out this character of approximation.[129]
Thus—it is not absolutely true that a movement is uniform and rectilinear. The theoretic law of the oscillation of a pendulum is unrealisable, because there is no non-resisting medium, no totally rigid and inextensible bar, no suspending apparatus capable of turning without friction. A planet could only describe an exact ellipse if it alone were turning round the sun: but as, in point of fact, there are several which act and react upon one another, Kepler’s law remains ideal. It is known by very accurate researches that Mariotte’s law of the relations between the density of a gas, and the pressure which it bears, is not strictly accurate for either; but the differences between theory and reality are so slight that, in ordinary cases, they are negligible. The laws of thermodynamics (conservation of energy, correlation of forces) which are so much used in the present day because of their character of generality, and are held by some to be the ultimate principle of phenomena, have no absolute value. It is not, e. g., correct to say that all change generates a change which can be re-transformed without loss or addition. The first moment of enthusiasm passed, there was no lack of criticism and of reservation on this point. And so in other instances, ad infinitum.
In brief, the concept of law, whenever it is more than a vague term in the mind, corresponds either to a direct condensation of facts (empirical laws), or to an ideal simplification (theoretical laws); but, imperfect or perfect, the mental process is the same in the two cases. They differ only in the degree of simplification attainable by analysis for any given material or datum. If empirical law, which is in strict relation with experience, has not been idolised, this distinction and misfortune has frequently befallen the other categories. It has been forgotten that, in the sciences as in the arts, the ideal is only an ideal, although it is here attained by different means, viz., elimination, voluntary omission for the sake of preciseness, a more or less artificial reduction to unity. Consequently many have fallen into the strange illusion of believing that, in manipulating experience by the labor of an ever-growing abstraction, the absolute can be brought out.[130]
SECTION VI. CONCEPT OF SPECIES.
In departing from phenomena by successive abstractions and generalisations, we rise to laws that are more and more extensive: so in setting out from the individual, species, genera, orders, branches, and the like, are formed by a succession of abstractions and generalisations. We have already followed this labor of the intellect in its primitive attempts to introduce order into the multiplicity and variety of living beings (Ch. III.). We saw its start in the period of generic images, its passage through the various degrees of the concrete-abstract period, and its final outcome by diverse paths into a unitary conception. We must now take up the subject from the point at which we left it, and consider the nature of the classificatory concepts at the final term of their development, the moment of their highest scientific determination. If the geometers were the first who abstracted from extension the essential data of Space; if the astronomers accomplished an analogous operation for Time; the naturalists for their part had by abstraction to disengage from among the numerous characteristics of living beings, those which, as fundamental, enable them to reduce individuals to species, species to genera, and so on. They are the inventors of the concepts which govern this province of experience.
The notion of the individual, which is the basis, and preliminary material, of biological classification, is sufficiently clear so long as we confine ourselves to the higher creatures; it becomes obscure and equivocal in descending to the lower grades, where life multiplies by budding, or by division. Hence it has been a great stumbling-block to the naturalists. For our purpose, the point is negligible. We can without inconvenience omit the debates on this subject, and presume that individuality always has its fixed characteristics. The work of abstraction and of generalisation alone concern us.
Among all others, the Concept of Species is certainly the one which—more especially in our own day—has been the most studied and disputed. Many efforts have been made to determine its essential characters, to which some attribute, and others refuse, an objective value. In effect, and broadly speaking—two contrary theories obtain in this connexion:
1. That of fixity of species, the oldest, and long paramount: still perhaps finding its partisans. If we accept this, we admit at the same time that the naturalist in determining species, reveals a mystery of nature, and partially discovers the plan of creation.
2. The complete antithesis of the foregoing, which maintains that only individuals exist. In its absolute and radical form, this assertion seems rarely to have been brought forward. It has, however, been said that “the idea of species is not given to us by nature itself.”[131] In point of fact, the contention of the transformists is different. They do not refuse to recognise the grouping of living beings, according to their degrees of similarity, into varieties and species; but they grant to species only a momentary fixedness in time and space. It does not exist, it is not a natural type, it is transitionally a stable variation; the individual is the reality. From our point of view, this signifies that the specific characters isolated by abstraction are of value only as practical means of simplification in no way helping us to penetrate into the nature of things.
However this may be,—and without for the moment inquiring whether the work of abstraction in this province gives objective or subjective results, whether it limits itself to simplification in relation to man, or discovers in relation to nature,—let us follow it in its ascending progress. Once again, we can distinguish two principal stages: that of species corresponding to empirical and concrete law; that of genera, and the still higher forms, corresponding to theoretical and ideal laws.
I.
The nature of a concept is fixed by the determination of its constituent elements; these are determined by abstraction. Abstraction that is not vulgar and arbitrary, but scientific, should disclose characteristics that are the substitutes for a group (here living beings in general), taking its place, and enabling us to think it. These constituent elements of the concept of species are met with in nearly all the naturalists’ definitions.[132] They are two in number; species is determined by two essential characteristics: similarity (morphological criterion), filiation (physiological criterion).
1. Similarity seems at first sight easy to determine—as though we had only to open our eyes; yet by this elementary procedure we hardly pass beyond the level of generic images, and there is risk of falling into many errors. It is necessary to penetrate into resemblances deeper than the superficial; and here is the first degree of complexity. Buffon observed that “the horse and the donkey, which are distinct species, resemble each other more than the water spaniel and the harrier, which are of the same species.” The facts which our contemporaries denote by the name of polymorphism, entirely baffle the criterion of similarity. Not to speak of the obvious difference between the larva and the perfect insect, the caterpillar and the butterfly, or between the males, females, and neuters of bees, ants, and termites; there are cases in which the disparity between the two sexes is so great that the male and the female, taken respectively as two different creatures, have been classified in distinct genera, and even orders: e. g., the lampyris or glow-worm, Lernea, and many others. The character of the resemblance is thus too often vague, sometimes deceptive, nearly always inadequate: it follows that we must resort to the other, to filiation.
2. This, the physiological criterion, again appears to leave no opening for equivocation, since it can be materially stated. Generally speaking, one is imbued with the notion that children resemble their parents, that the immediate product is the reproduction of the type of the progenitors. But the alternating generations (metagenesis, geneagenesis) discovered in the course of the present century, show that this conception is too simple, and often fallacious. This mode of reproduction is by no means rare; we meet with it among a great number of the lower plants, infusoria, worms, and even insects. “The dominating fact in the reproduction of all these creatures, is that a sexual being, of definite form, gives birth to a-sexual beings which do not resemble it, but which in their turn produce by a sort of budding, or by fission of their bodies, the sexual creatures similar to those from which they issued.” Vogt, accordingly, in his definition of species, is forced to include the case of alternate generation by saying: “Species is the reunion of all the individuals that originate from the same parents, and are in themselves, or in their descendants, similar to their primordial ancestors.”
In brief, the general notion of species depends upon two ideas, complex notwithstanding their apparent simplicity, fluctuating in spite of their apparent precision.
Till now, we have spoken of species as if it were directly superposed upon individuals, as if it resulted from immediate generalisation. This is not the naturalists’ position. Their classification descends from the species to the individual by decreasing generalisations of the race and the variation. Thus the human species comprises several races (white, yellow, etc.), the white race comprises several variations (English, Arab type, etc.). To the partisan of fixedness of species, these three general notions have not the same value: species alone has peculiar and irreducible characters, which are deduced from the function of reproduction and the facts of cross-breeding.
Couple two individuals of distinct species: the union is generally sterile. If otherwise, the hybrids which result from it are unfruitful. If, as rarely happens, they propagate themselves, the offspring rapidly return to the type of one of the ancestral species.
Couple two individuals of distinct races or variations, the union will be fruitful; the resulting cross-breeds are again fertile; the progenitors are able to create and fix varieties, and even races.
Hence, it is concluded, species must be a thing that exists, that protects itself, does not let itself be encroached upon.
Evidently the debated question is one of facts: and both the parties in dispute adduce experimental evidence. Few in number as they may be, there are fertile hybrids, which perpetuate themselves. They are found among birds and mammals, e. g., the alpaca and the vicuna, the bull and the zebu, the goat and the sheep—which have for issue the ovicaprinæ,—the hare and the rabbit—whose offspring is the leporide, (their perpetuity has been contested). On the other hand, if certain species have thus been formed by a durable blend, there exist races that have been refractory to all attempts at cross-breeding: i. e., the domestic and Brazilian guinea-pig, different races of rats, of rabbits, etc.
We need not enter into the discussion, nor enumerate the observations and experiments invoked on either side: they are to be found in special works. Our aim was to discover the constituent elements of the notion of species in its scientific aspect. Now, neither the morphological element nor the physiological element has any distinguishing mark of permanence and universality. The concept of species is possessed of no absolute value; neither is it a simple replica in the mind of the “plan of nature.” The result of abstraction and of generalisation, it corresponds to something which is fixed for a certain time in certain conditions; it has temporary and provisional objectivity.[133]
II.
Contemporary discussion is almost entirely centred upon species. Little is said about genera, and still less of the higher divisions. We do not, in any case, find what we require: the determination of constitutive elements, of general acceptance, which shall be for the genus, family, order, or class, the equivalent of the two denotative marks—morphological and physiological—that are attributed to species.
This has not always been the case. At the time when there was general belief in a scheme of creation, the naturalists were careful, by bringing together species, genera, families, etc., to disengage more and more general characters, which they regarded as essential, and determined by the nature of the thing. We have already said that Linnæus was the first to formulate a precise notion of genus, to which he expressly attributed a reality: “You must know,” he says, in his Philosophia botanica, “that it is not character that constitutes the genus, but genus the character; that character devolves from genus, not genus from character; that character exists not in order that genus should come about (fiat), but so that the genus should be known.” In the binary nomenclature which he adopted, the first term designates the genus, the second one of the species included. Thus the dog and the wolf have characters by which they resemble each other, and are distinguished from other animals (five fingers on the anterior limbs, four only on the posterior, twenty-two teeth in the upper and lower jaw, etc.) Linnæus classifies them as the genus Canis, of which Canis familiaris, Canis lupus, Canis vulpes, etc., are the species. Again, the genus Felis, determined by the characters common to certain animals exclusively, comprises in its species: the cat (Felis catus), the lion (Felis leo), the tiger (Felis tigris), etc.
Agassiz, the last representative of the line of naturalists who aspired at reproducing the order of nature in the hierarchy of their classificatory concepts, characterises the genera and divisions superior to them by vague formulæ. Of these we can judge from the following passage:
“Individuals are the support, at the actual moment, of the characters not merely of species, but of all other divisions. As representative of genus, they have certain details of a definite and specific structure, identical with those possessed by the representatives of other species. As representative of family, they have a definite constitution, expressive of a distinct and specific model, in forms resembling those of the representatives of other genera. As representative of order, they take definite rank, as compared with the representatives of other families. As representative of class, they manifest the structural plan of their ramifications by the aid of special means, and according to specific directions. As representative of branches the individuals are all organised on a distinct plan which differs from the plan of other branch-lines.”[134]
It was shown above (Ch. III.) that the contemporary classifications, which are radically embryological, transformist, and generic, proceed otherwise, and have a different aim. Their ideal is to draw up the genealogical tree of living beings, with its multiple ramifications, marking the principal moments of evolution.
But if, leaving aside the material of these (animal or vegetable) classifications, we consider only the psychological labor by which they are constituted, we find that the transformists and their adversaries have at least one common point which is of cardinal importance. The notion of fundamental types—conceived as fixed or provisory—is for the one as for the other a compass, a guide in research, a normal, by means of which deviations are appreciated. Hence, these concepts have a practical value, and it is true that we find abstraction and generalisation in their principal rôle, which is, not to discover, but to simplify, above all to be useful.
In effect, the one side, yielding to the natural tendency of the mind to reify abstractions, admit the permanence and objectivity of types: they believe firmly that they have in certain concepts the possibility of an ideal reconstruction of the entire world of living beings. This faith sustains them and urges them on to more and more exact determinations.
Their opponents, the transformists of every degree, are guided by a different ideal; they search after continuity, transition, forms of passage. Species, genera, families, etc., are but provisory starting-points, with intermediate lacunæ which they endeavor to bridge over. Although the animal order, the chain of life, is itself only a theoretical construction, a natural abstraction, many fine works could be quoted which are inspired by this faith in continuity. Such, e. g., are Huxley, Cope, and others upon the genus Equus, establishing the filiation of the four-fingered Eohippus of the old Tertiary epoch, with the Hipparion of the new Tertiary epoch, and with the Horse of the Quaternary period.
The hierarchy of concepts formed by superposition of abstractions and generalisations only facilitates the task. The sole incontestable value that can be assigned to any notion of species, and still more to genus, and other still more general concepts, is that of utility. They are successful implements in the investigation of nature. All other pretensions are open to discussion. One position more especially is untenable: that which claims for concepts, the pure results of abstraction, an absolute value. It is obvious that they can have none. They are neither reality nor fiction, but approximations.
Laws and species—two general notions which must be connected—were bound to vary in the course of evolution, because they are entirely subordinated to the conditions which govern the existence of phenomena and of living beings. Let us—merely as an illustration to fix our ideas—admit the hypothesis of a primitive nebula. Imagine (which is impossible) an intelligent being, able, at that point in the world’s history, to draw up a scheme of the existing laws. He could discover none but those which govern matter in the gaseous state,—some of which are still extant, others unknown to us, and unknowable—since, their conditions of existence having ceased, they are annihilated. When at a later time this matter, uniformly diffused and dispersed through space, became divided from one or other cause into vast nebulous spheres commencing their slow revolution, our hypothetical being might have surprised the birth of the astronomical laws. Subsequently, the constitution of the liquid state of matter, and then of the solid state in its different degrees, would give birth to new physico-chemical laws, others meantime disappearing. When, finally, life—whatever may have been its origin—appeared, other laws again loomed forth, and the possibility of classification. Yet to the hypothetical spectator, these must needs be highly singular, highly dissimilar from our own—unless we admit the hypothesis of a world created at one throw.
It is needless to enter into the details of this long evolution, as it is generally admitted to have been. Enough to remember that the matter whence abstraction deduces laws and species has varied, and may vary again in the course of ages. If, on the other hand, we consider the slow progress of human knowledge, and the incessant corrections imposed by experience and reasoning from century to century, we find ourselves confronted with two variable factors, one objective, the other subjective. No permanence can result from their union. Long as may be the stability of laws and species, nothing guarantees their perpetual duration. So that after two centuries which make a brave show in the history of the sciences, we may still advance the formula of Leibnitz: “Our determinations of physical species are provisional and proportional to our knowledge.”[135]
Many other concepts might be added to the preceding, among them, those of the moral sciences. I forbear, because the history of their fluctuations would in itself exact a volume. Till now, these have been ill-determined, badly defined. May we even speak of any regular evolution? Have they not rather suffered corsi e ricorsi, which bring them back perennially to their point of departure? Whenever—during a development of centuries—the work of abstraction has succeeded, we have seen it pass through successive phases:—generic ideas, intermediate forms, higher forms—but not by any constant process. Sometimes it has rapidly attained the period of complete simplification, as in mathematics; sometimes it is long arrested in its progress, as in the natural sciences: sometimes, again, as in the less established sciences, it is incapable even to the present day of transcending the lowest stages.