Therefore, it is very evident the above definition is much too wide, and does not agree with _solo definito_. It does not succeed in disengaging the essential characteristic of physics. This characteristic indeed exists, and we foresee it, but we do not formulate it.

Another definition by content has not been much more happy. To separate the material from the moral, the conception of Descartes was remembered, and we were told that: "Psychology is the science of what exists only in time, while physics is the science of what exists at once in time and in s.p.a.ce."

To this theoretical reasoning it might already be objected that, in fact, and in the life we lead, we never cease to localise in s.p.a.ce, though somewhat vaguely, our thought, our Ego, and our intellectual whole. At this moment I am considering myself, and taking myself as an example. I am writing these lines in my study, and no metaphysical argument can cause me to abandon my firm conviction that my intellectual whole is in this room, on the second floor of my house at Meudon. I am here, and not elsewhere. My body is here; and my soul, if I have one, is here. I am where my body is; I believe even that I am within my body.

This localisation, which certainly has not the exactness nor even the characteristics of the localisation of a material body in s.p.a.ce, seems to me to result from the very great importance we attach, to the existence of our body in perception and in movement. Our body accompanies all our perceptions; its changes of position cause these perceptions to vary; the accidents which happen to it bring us pleasure or pain. Some of its movements are under our orders; we observe that others are the consequences of our thoughts and our emotions. It occupies, therefore, among the objects of cognition a privileged place, which renders it more intimate and more dear to us than other objects. There is no need to inquire here whether, in absolute reality, I am lodged within it, for this "I" is an artificial product manufactured from memories. I have before explained what is the value of the relation subject-object. It is indisputable that in the manufacture of the subject we bring in the body. This is too important an element for it not to have the right to form part of the synthesis; it is really its nucleus. As, on the other hand, all the other elements of the synthesis are psychical, invisible, and reduced to being faculties and powers, it may be convenient to consider them as occupying the centre of the body or of the brain. There is no need to discuss this synthesis, for it is one of pure convenience. As well inquire whether the personality of a public company is really localised at its registered offices, round the green baize cover which adorns the table in the boardroom.

Another definition of psychology, which is at once a definition by content and a definition by method, has often been employed by philosophers and physiologists. It consists in supposing that there really exist two ways of arriving at the cognition of objects: the within and the without. These two ways are as opposed to each other as the right and wrong side of a stuff. It is in this sense that psychology is the science of the within and looks at the wrong side of the stuff, while the natural sciences look at the right side. And it is so true, they add, that the same phenomenon appears under two radically different forms according as we look at it from the one or the other point of view. Thus, it is pointed out to us, every one of our thoughts is in correlation with a particular state of our cerebral matter; our thought is the subjective and mental face; the corresponding cerebral process is the objective and material face.

Then the difference between representation, which is a purely psychological phenomenon, and a cerebral state which is a material one, and reducible to movement, is insisted upon; and it is declared that these two orders of phenomena are separated by irreducible differences.

Lastly, to take account of the meaning of these differences, and to explain them, it is pointed out that they are probably connected with the modes of cognition which intervene to comprehend the mental and the physical. The mental phenomenon, we are told, is comprehended by itself, and as it is; it is known without any mystery, and in its absolute reality. The physical phenomenon, on the contrary, only reaches us through the intermediary of our nerves, more or less transformed in consequence by the handling in transport. It is an indirect cognition which causes us to comprehend matter; we have of this last only a relative and apparent notion, which sufficiently explains how it may differ from a phenomenon of thought.

I have already had occasion to speak of this dualism, when we were endeavouring to define sensation. We return to its criticism once more, for it is a conception which in these days has become cla.s.sic; and it is only by repeatedly attacking it that it will be possible to demonstrate its error.

To take an example: I look at the plain before me, and see a flock of sheep pa.s.s over it. At the same time an observer is by my side and is not looking at the same thing as myself. It is not at the plain that he looks; it is, I will suppose, within my brain. Armed with a microscope _a la_ Jules Verne, he succeeds in seeing what is pa.s.sing beneath my skull, and he notices within my fibres and nerve cells those phenomena of undulation which physiologists have hitherto described hypothetically. This observer notices then, that, while I am looking over the plain, my optic nerve conveys a certain kind of movements--these are, I suppose, displacements of molecules which execute a complicated kind of dance. The movement follows the course of the optic nerve, traverses the chiasma, goes along the fascia, pa.s.ses the internal capsule, and finally arrives at the visual centres of the occipital region. Here, then, are the two terms of comparison const.i.tuted: on the one hand, we have a certain representation--that is, my own; and on the other hand, coinciding with this representation we have the dynamic changes in the nerve centres. These are the two things const.i.tuting the right and wrong side of the stuff. We shall be told: "See how little similarity there is here! A representation is a physical fact, a movement of molecules a material fact." And further, "If these two facts are so little like each other, it is because they reach us by two different routes."

I think both these affirmations equally disputable. Let us begin with the second. Where does one see that we possess two different sources of knowledge? Or that we can consider an object under two different aspects? Where are our duplicate organs of the senses, of which the one is turned inward and the other outward? In the example chosen for this discussion, I have supposed two persons, each of whom experiences a visual perception. One looks at one object, the other at another; but both are looking with the same organs of sense, that is, with their eyes. How is it possible to understand that these eyes can, in turn, according to the necessity of the moment, see the two faces, physical and mental, of the same object?

They are the two faces of an identical object, is the answer made to us, because the two visions, although applied to the same object, are essentially different. On the one hand is a sensation of displacement, of movement, of a dance executed by the molecules of some proteid substance; on the other hand is a flock of sheep pa.s.sing over the plain at a distance of a hundred metres away.

It seems to me that here also the argument advanced is not sound. In the first place, it is essential to notice that not only are the two paths of cognition identical, but also that the perceptions are of the same nature. There is in this no opposition between the physical and the mental. What is compared are the two phenomena, which are both mixed and are physico-mental--physical, through the object to which they are applied, mental, through the act of cognition they imply. To perceive an object in the plain and to perceive a dynamic state of the brain are two operations which each imply an act of cognition; and, in addition, the object of this knowledge is as material in the one as in the other case. A flock of sheep is matter just as much as my brain.

No doubt, here are objects which differ; my observer and myself have not the same perception. I acknowledge, but do not wonder at it. How could our two perceptions be similar? I look at the sheep, and he at the interior of my brain. It is not astonishing that, looking at such different objects, we should receive images also different. Or, again, if this other way of putting it be preferred, I would say: the individual A looks at the flock through the intermediary of his nervous system, while B looks at it through that of two nervous systems, put as it were end to end (though not entirely), his own nervous system first, and then that of A. How, then, could they experience the same sensation?

They could only have an identical sensation if the idea of the ancients were to be upheld, who understood the external perception of bodies to result from particles detaching themselves from their bodies, and after a more or less lengthy flight, striking and entering into our organs of sense.[36]

Let us imagine, just for a moment, one of our nerves--the optic nerve, for instance--transformed into a hollow tube, along which the emissions of miniatures should wend their way. In this case, evidently, if so strange a disposition were to be realised, and if B could see what was flowing in the optic nerve of A, he would experience a sensation almost a.n.a.logous to that of A. Whenever the latter saw a dog, a sheep, or a shepherd, B would likewise see in the optic ca.n.a.l minute dogs, microscopic sheep, and Lilliputian shepherds.

At the cost of such a childish conception, a parity of content in the sensations of our two spectators A and B might be supposed. But I will not dwell on this.

The above considerations seem to me to explain the difference generally noticed between thought and the physiological process. It is not a difference of nature, an opposition of two essences, or of two worlds--it is simply a difference of object; just that which separates my visual perception of a tree and my visual perception of a dog.

There remains to know in what manner we understand the relation of these two processes: this is another problem which we will examine later.

Since the content does not give us the differentiation we desire, we will abandon the definitions of psychology by content. What now remains? The definitions from the point of view. The same fact may he looked at, like a landscape, from different points of view, and appears different with the changes therein. It is so with the facts we consider psychical, and the autonomy of psychology would thus be a matter of point of view.

It has, then, been supposed--and this is a very important proposition--that the distinctive feature of psychical facts does not consist in their forming a cla.s.s of particular events. On the contrary, their characteristic is to be studied in their dependency on the persons who bring them about. This interesting affirmation is not new: it may be read in the works of Mach, Kulpe, Munsterberg, and, especially, of Ebbinghaus, from whom I quote the following lines of quite remarkable clearness: "Psychology is not distinguished from sciences like physics and biology, which are generally and rightly opposed to it, by a different content, in the way that, for instance, zoology is distinguished from mineralogy or astronomy. It has the same content, but considers it from a different point of view and with a different object. It is the science, not of a given part of the world, but of the whole world, considered, however, in a certain relation. It studies, in the world, those formations, processes, and relations, the properties of which are essentially determined by the properties and functions of an organism, of an organised individual.... Psychology, in short, considers the world from an individual and subjective point of view, while the science of physics studies it as if it were independent of us."

Over these definitions by point of view, one might quibble a little; for those who thus define psychology are not always consistent with themselves. In other pa.s.sages of their writings they do not fail to oppose psychical to physiological phenomena, and they proclaim the irreducible heterogeneity of these two orders of phenomena and the impossibility of seeing in physics the producing cause of the moral.

Ebbinghaus is certainly one of the modern writers who have most strongly insisted on this idea of opposition between the physiological and the psychical, and he is a convinced dualist. Now I do not very clearly understand in what the principle of heterogeneity can consist to a mind which admits, on the other hand, that psychology does not differ from the physical sciences by its content.

However, I confine myself here to criticising the consequences and not the starting point. The definition of the psychical phenomenon by the point of view seems to me correct, although it has more concision than clearness; for it rests especially upon a material metaphor, and the expression "point of view" hardly applies except to the changes of perspective furnished by visible objects.

It would be more exact to say that psychology specially studies certain objects of cognition, such as those which have the character of representations (reminiscences, ideas, concepts), the emotions, the volitions, and the reciprocal influences of these objects among themselves. It studies, then, a part of the material world, of that world which till now has been called psychological, because it does not come under the senses, and because it is subjective and inaccessible to others than ourselves; it studies the laws of those objects, which laws have been termed mental.[37]

These laws are not recognised, popularly speaking, either in physics or in biology; they const.i.tute for us a cognition apart from that of the natural world. a.s.sociation by resemblance, for example, is a law of consciousness; it is a psychological law which has no application nor counterpart in the world of physics or biology. We may therefore sum up what has been said by the statement that psychology is the study of a certain number of laws, relations, and connections.

As to the particular feature which distinguishes mental from physical laws, we can formulate it, as does William James, by saying that the essence of a mental law is to be teleological, or, if the phrase be preferred, we can say that mental activity is a finalistic activity, which expends itself as will in the pursuit of future ends, and as intelligence in the choice of the means deemed capable of serving those ends. An act of intelligence is recognised by the fact of its aiming at an end, and employing for this end one means chosen out of many. Finality and intelligence are thus synonymous. In opposition to mental law, physical law is mechanical, by which expression is simply implied the absence of finality. Finality opposed to mechanism; such is the most concise and truest expression in which must be sought the distinctive attribute of psychology and of the moral sciences, the essential characteristic by which psychological are separated from physical facts.

I think it may be useful to dwell a little on the mental laws which I have just opposed to the physical, and whose object is to a.s.sure preadaptation and form a finality.[38] Their importance cannot be exaggerated. Thanks to his power of preadaptation, the being endowed with intelligence acquires an enormous advantage over everything which does not reason. No doubt, as has been shrewdly remarked, natural selection resembles a finality, for it ends in an adaptation of beings to their surroundings. There is therefore, strictly speaking, such a thing as finality without intelligence. But the adaptation resulting therefrom is a crude one, and proceeds by the elimination of all that does not succeed in adapting itself; it is a butchery. Real finalism saves many deaths, many sufferings, and many abortions.[39]

Let us examine, then, the process of preadaptation; it will enable us to thoroughly comprehend, not only the difference between the physical and the psychical laws, but the reason why the psychical manages in some fashion to mould itself upon the physical law.

Now, the means employed by preadaptation is, if we take the matter in its simplest form, to be aware of sensations before they are experienced. If we reflect that all prevision implies a previous knowledge of the probable trend of events, it will be understood that the part played by intelligence consists in becoming imbued with the laws of nature, for the purpose of imitating its workings. By the laws of nature, we understand here only that order of real sensations, the knowledge of which is sufficient to fulfil the wants of practical life. To us there are always gaps in this order, because the sensation it is important for us to know is separated from us either by the barriers of time or of s.p.a.ce, or by the complication of useless sensations. Thence the necessity of interpolations. That which we do not perceive directly by our senses, we are obliged to represent to ourselves by our intelligence; the image does the work of sensation, and supplements the halting sensation in everything which concerns adaptation.

To replace the inaccessible sensation by the corresponding image, is therefore to create in ourselves a representation of the outer world which is, on all the points most useful to us, more complete than the direct and sensorial presentation of the moment. There is in us a power of creation, and this power exercises itself in the imitation of the work of nature; it imitates its order, it reconst.i.tutes on the small scale adapted to our minds, the great external order of events.

Now, this work of imitation is only really possible if the imitator has some means at his disposal a.n.a.logous to those of the model.

Our minds could not divine the designs of nature, if the laws of images had nothing in common with the laws of nature. We are thus led to confront these two orders of laws with each other; but, before doing so, one more preliminary word is necessary. We have up till now somewhat limited the problem, in order to understand it. We have reduced the psychological being to one single function, the intellectual, and to one single object of research, the truth. This is, however, an error which has often been committed, which is now known and catalogued, called intellectualism, or the abuse of intellectualism. It is committed for this very simple reason, that it is the intellectual part of our being which best allows itself to be understood, and, so to speak, intellectualised. But this leaves out of the question a part of our entire mental being so important and so eminent, that if this part be suppressed, the intelligence would cease to work and would have no more utility than a machine without motive power. Our own motive power is the will, the feeling, or the tendency.

Will is perhaps the most characteristic psychical function, since, as I have already had occasion to say, nothing a.n.a.logous to it is met with in the world of nature. Let us therefore not separate the will from the intelligence, let us incarnate them one in the other; and, instead of representing the function of the mind as having for its aim knowledge, foresight, the combination of means, and self-adaptation, we shall be much nearer the truth in representing to ourselves a being who _wills_ to know, _wills_ to foresee, and _wills_ to adapt himself, for, after all, he _wills_ to live.

Having said this, let us compare the psychological law and that of nature. Are they identical? We shall be told that they are not, since, as a fact, errors are committed at every moment by the sudden failures of human reason. This is the first idea which arises. Human error, it would seem, is the best proof that the two laws in question are not alike, and we will readily add that a falling stone does not mistake its way, that the crystal, in the course of formation does not miss taking the crystalline shape, because they form part of physical nature, and are subject in consequence to its determinism. But this is faulty reasoning, and a moment of reflection demonstrates it in the clearest possible manner; for adaptation may miss its aim without the being who adapts himself and his surroundings necessarily obeying different laws. When the heat of a too early spring causes buds to burst forth prematurely which are afterwards destroyed by frost, there is produced a fault of adjustment which resembles an error of adaptation, and the bringing forward of this error does not necessarily imply that the tree and the whole of physical nature are obeying different laws. Moreover, the difference between the laws of nature and those of the understanding does not need deduction by reasoning from an abstract principle; it is better to say that it is directly observable, and this is how I find that it presents itself to us.

The essential law of nature is relatively easy to formulate, as it is comprised in the very definition of law. It simply consists in the sentence: uniformity under similar conditions. We might also say: a constant relation between two or several phenomena, which can also be expressed in a more abstract way by declaring that the law of nature rests on the combination of two notions, ident.i.ty and constancy.

On the other hand, the laws of our psychical activity partly correspond to the same tendencies, and it would be easy to demonstrate that the microcosm of our thoughts is governed by laws which are also an expression of these two combined notions of constancy and ident.i.ty.

It is, above all, in the working of the intellectual machine, the best known and the most clearly a.n.a.lysed up till now, that we see the application of this mental law which resembles, as we say, on certain sides, the physical law: and the best we can do for our demonstration will doubtless be to dissect our reasoning powers. Reason, a process essential to thought in action, is developed in accordance with a law which resembles in the most curious manner a physical law. It resembles it enough to imitate it, to conform to it, and, so to speak, to mould itself on it.

Now, the reason does not follow the caprices of thought, it is subject to rules; it results from the properties of the images, those properties which we have above referred to, the material character of which we have recognised, and which are two in number--similarity and contiguity, as they are termed in the jargon of the schools. They are properties which have for their aim to bring things together, to unite, and to synthetise. They are unceasingly at work, and so apparent in their labour that they have long been known. We know, since the time of Aristotle, that two facts perceived at the same time reproduce themselves together in the memory--this is the law of contiguity; and that two facts perceived separately, but which are similar, are brought together in our mind--this is the law of similarity.

Now, similarity and contiguity form by combination the essential part of all kinds of reasoning, and this reasoning, thus understood, works in a fashion which much resembles (we shall see exactly in what degree) a physical law. I wish to show this in a few words. What renders my demonstration difficult and perhaps obscure is, that we shall be obliged to bring together rather unexpectedly categories of phenomena which are generally considered separate.

The distinctive attribute of the reason consists, as I have said, in the setting to work of these two elementary properties, similarity and contiguity. It consists, in fact, in extending continuity by similarity; in endowing with identical properties and similar accompaniments things which resemble each other; in other words, it consists in impliedly a.s.serting that the moment two things are identical in one point they are so for all the rest. This will be fairly well understood by imagining what takes place when mental images having the above-mentioned properties meet. Suppose that B is a.s.sociated with C, and that A resembles B. In consequence of their resemblance the pa.s.sing from A to B is easy; and then B suggesting C by contiguity, it happens that this C is connected with A connected, though, in reality, they have never been tried together. I say they are a.s.sociated on the basis of their relation to B, which is the rallying point. It is thus that, on seeing a piece of red-hot iron (A), I conclude it is hot (C), because I recollect distinctly or unconsciously another piece of red-hot iron (B), of which I once experienced the heat. It is this recollection B which logicians, in their a.n.a.lysis of logical, verbal, and formal argument, call the middle term. Our representation of the process of reasoning is not special to argument. It also expresses the process of invention, and every kind of progress from the known to the unknown. It is an activity which creates relations, which a.s.sembles and binds together, and the connections made between different representations are due to their partial ident.i.ties, which act as solder to two pieces of metal.

It will now be understood that these relations between the images curiously resemble the external order of things, the order of our sensations, the order of nature, the physical law. This is because this physical law also has the same character and expresses itself similarly. We might say "all things which resemble each other have the same properties," or "all things alike on one point resemble each other on all other points." But immediately we do so, the difference between the physical and the mental law becomes apparent. The formula we have given is only true on condition that many restrictions and distinctions are made.

The process of nature is so to do that the _same_ phenomenon always unfolds itself in the same order. But this process is not always comprehended in real life, for it is hidden from our eyes by the manifold combinations of chance; in the reality that we perceive there is a crowd of phenomena which resemble each other but are not really the same. There are a number of phenomena which co-exist or follow each other without this order of co-existence or succession being necessary or constant. In other words, there are resemblances which are the marks of something, as a logician would say, and others which are not the marks of anything; there are relations of time and s.p.a.ce which are the expression of a law; there are some which are accidental, and may possibly never be reproduced.

It would be a wonderful advantage if every scientific specialist would make out a list of the non-significant properties that he recognises in matter. The chemist, for example, would show us that specific weight has hardly any value in diagnosis, that the crystalline form of a salt is often not its own, that its colour especially is almost negligible because an immense number of crystals are white or colourless, that precipitation by a given substance does not ordinarily suffice to characterise a body, and so on. The botanist, on his part, would show us that, in determining plants, absolute dimension is less important than proportion, colour less important than form, certain structures of organs less important than others.

The pathologist would teach us that most pathological symptoms have but a trivial value; the cries, the enervation, the agitation of a patient, even the delirium which so affects the bystanders, are less characteristic of fever than the rate of his pulse, and the latter less than the temperature of the armpit or the dryness of the tongue, &c. At every moment the study of science reveals resemblances of facts and contiguities of facts which must be neglected for the sake of others. And if we pa.s.s from this profound knowledge of the objects to the empirical knowledge, to the external perception of bodies, it is in immense number that one espies around one traps laid by nature. The sound we hear resembles several others, all produced by different causes; many of our visual sensations likewise lend themselves to the most varied interpretations; by the side of the efficient cause of an event we find a thousand entangled contingencies which appear so important that to disentangle them we are as much perplexed as the savage, who, unable to discriminate between causes and coincidences, returns to drink at the well which has cured him, carefully keeping to the same hour, the same gestures, and the same finery.

The reason of this is that the faculty of similarity and the faculty of contiguity do not give the distinction, necessary as it is, between resemblances and co-existences which are significant and those which are not. The causal nexus between two phenomena is not perceived as something apart and _sui generis_; it is not even perceived at all. We perceive only their relation in time and s.p.a.ce, and it is our mind which raises a succession to the height of a causal connection, by intercalating between cause and effect something of what we ourselves feel when we voluntarily order the execution of a movement. This is not the place to inquire what are the experimental conditions in which we subject phenomena to this anthropomorphic transformation; it will suffice for us to repeat here that, in perception, a chance relation between phenomena impresses us in the same way as when it is the expression of a law.

Our intellectual machine sometimes works in accord with the external law and at others makes mistakes and goes the wrong way. Then we are obliged to correct it, and to try a better adjustment, either by profounder experimenting with nature (methods of concordance, discordance, variations, &c.), or by a comparison of different judgments and arguments made into a synthesis; and this collaboration of several concordant activities ends in a conclusion which can never represent the truth, but only the probable truth. The study of the laws of the mind shows us too clearly, in fact, their fluidity with regard to the laws of nature for us not to accept probabilism. There exists no cert.i.tude--only very varied degrees of probability. Daily practice contents itself with a very low degree of probability; judicial logic demands a rather higher one, especially when it is a question of depriving one of our fellow-creatures of liberty or life.

Science claims one higher still. But there is never anything but differences of degrees in probability and conjecture.

This, then, is the definition of psychology that we propose. It studies a certain number of laws which we term mental, in opposition to those of external nature, from which they differ, but which, properly speaking, do not deserve the qualification of mental, since they are--or at least the best known of them are--laws of the images, and the images are material elements. Although it may seem absolutely paradoxical, psychology is a science of matter--the science of a part of matter which has the property of preadaptation.

FOOTNOTES:

[Footnote 33: LANGE, _Histoire du Materialisme_, II., 2me. partie, chap. iii.]

[Footnote 34: Let us remark, in pa.s.sing, how badly nature has organised the system of communication between thinking beings. In what we experience we have nothing in common with our fellows; each one experiences his own sensations and not those of others. The only meeting point of different minds is found in the inaccessible domain of the _noumena._]

[Footnote 35: E. RABIER, _Lecons de Philosophie_, "Psychologie," p.

33.]

[Footnote 36: This seems to have been the opinion of Democritus. The modern doctrine of radiation from the human body, if established, would go nearly as far as the supposition in the text. Up till now, however, it lacks confirmation.--ED.]

[Footnote 37: I am compelled, much against my will, to use throughout this pa.s.sage an equivocal expression, that of "mental law," or law of consciousness, or psychological law. I indicate by this the laws of contiguity and of similarity; as they result from the properties of the images, and as these are of a material nature, they are really physical and material laws like those of external nature. But how can all these laws be called physical laws without running the risk of confusing them one with the other?]