In the main the arguments of the metaphysicians given above appear to me to contain a grave error. This consists in supposing that the natural sciences study the reality hidden beneath sensation, and only make use of this fact as of a sign which enables them to get back from effect to cause. This is quite inexact. That the natural sciences are limited by sensation is true; but they do not go outside it, they effect their constructions with sensation alone. And the reason is very simple: it is the only thing they know. To the metaphysical psychologist, who claims sensation as his own property, saying, "But this sensation is a state of my consciousness, it is mine, it is myself," the physicist has the right to answer: "I beg your pardon! this sensation is the external object that I am studying; it is my column of mercury, my spring, my precipitate, my amœba; I comprehend these objects directly, and I want no other." Psychology finds itself, therefore, exactly on the same footing as the other sciences in the degree in which it studies sensations that it considers as its own property. I have already said that the sensations proper to psychology are hardly represented otherwise than by the emotional sensations produced by the storms in the apparatus of organic life.
We now come to the definitions by content. They have been numerous, but we shall only quote a few. The most usual consists in saying, that Psychology studies the facts of consciousness. This formula passes, in general, as satisfactory. The little objection raised against it is, that it excludes the unconscious facts which play so important a part in explaining the totality of mental life; but it only requires some usual phrase to repair this omission. One might add, for instance, to the above formula: conscious facts and those which, while unconscious under certain conditions, are yet conscious in others.
This is not, however, the main difficulty, which is far more serious. On close examination, it is seen that the term, fact of consciousness, is very elastic, and that for a reason easy to state. This is, that all facts which exist and are revealed to us reach us by the testimony of the consciousness, and are, consequently, facts of consciousness. If I look at a locomotive, and analyse its machinery, I act like a mechanic; if I study under the microscope the structure of infusoria, I practise biology; and yet the sight of the locomotive, the perception of the infusoria, are just facts of consciousness, and should belong to psychology, if one takes literally the above definition, which is so absolute that it absorbs the entire world into the science of the mind. It might, indeed, be remarked that certain phenomena would remain strictly psychological, such as, for instance, the emotions, the study of which would not be disputed by any physical science; for the world of nature offers us nothing comparable to an emotion or an effort of will, while, on the other hand, everything which is the object of physical science—that is, everything which can be perceived by our external senses—may be claimed by psychology. 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 space."
To this theoretical reasoning it might already be objected that, in fact, and in the life we lead, we never cease to localise in space, 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 space, 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 classic; and it is only by repeatedly attacking it that it will be possible to demonstrate its error.