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Going on with our inventory, after sensations come images, ideas, and concepts; in fact, quite a collection of phenomena, which are generally considered as essentially psychological.

So long as one does not carefully analyse the value of ideas, one remains under the impression that ideas form a world apart, which is sharply distinguished from the physical world, and behaves towards it as an antithesis. For is not conception the contrary of perception? and is not the ideal in opposition to reality?

Thoughts have some characteristics of fancy, of freedom, even of unreality, which are wanting to the prosaicness of heavy material things. Thoughts sport with the relations of time and space; they fly in a moment across the gulf between the most distant objects; they travel back up the course of time; they bring near to us events centuries away; they conceive objects which are unreal; they imagine combinations which upset all physical laws, and, further, these conceptions remain invisible to others as well as to ourselves. They are outside the grip of reality, and constitute a world which becomes, for any one with the smallest imagination, as great and as important as the world called real. One may call in evidence the poets, novelists, artists, and the dreamers of all kinds. When life becomes too hard for us, we fly to the ideal world, there to seek forgetfulness or compensation.

It is, therefore, easy to understand, that it should have been proposed to carry into ideation the dichotomy between the physical and the moral. Many excellent authors have made the domain of the mind begin in the ideal. Matter is that which does not think. Descartes, in his Discours de la Méthode (4th part), remarking that he may pretend “not to have a body, and that there is no world or place in which he exists, but that he cannot pretend that he does not think,” concludes by saying that the mind is “a substance, all whose essence or nature is merely to think, and which has no need of either place or any other material thing, in order to exist;” in short, that “the soul is absolutely distinct from the body.”[1] Let us, then, examine in what measure this separation between perception and ideation can be legitimately established. If we accept this separation, we must abandon the distinction I proposed between acts and objects of cognition, or, at least, admit that this distinction does not correspond to that between the physical and the moral, since thoughts, images, recollections, and even the most abstract conceptions, all constitute, in a certain sense, objects of cognition. They are phenomena which, when analysed, are clearly composed of two parts, an object and a cognition. Their logical composition is, indeed, that of an external perception, and there is in ideation exactly the same duality as in sensation. Consequently, if we maintain the above distinction as a principle of classification for all knowable phenomena, we shall be obliged to assign the same position to ideas as to sensations.

The principal difference we notice between sensation and idea is, it would seem, the character of unreality in the last named; but this opposition has not the significance we imagine. Our mental vision only assumes this wholly special character of unreality under conditions in which it is unable to harmonise with the real vision. Taine has well described the phases of the reduction of the image by sensation: it is at the moment when it receives the shock of an image which contradicts it, that the image appears as illusory.[2] Let us suppose that we are sitting down, dreaming and watching the passing by of our images. If, at this moment, a sudden noise calls us back to reality, the whole of our mental phantasmagoria disappears as if by the wave of a magic wand, and it is by thus vanishing that the image shows its falsity. It is false because it does not accord with the present reality.

But, when we do not notice a disagreement between these two modes of cognition, both alike give us the impression of reality. If I evoke a reminiscence and dwell attentively on the details, I have the impression that I am in face of the reality itself. “I feel as if I were there still,” is a common saying; and, among the recollections I evoke, there are some which give me the same certitude as the perception of the moment. Certain witnesses would write their depositions with their blood. One does not see this every day; but still one does see it.

Further, there are thousands of circumstances where the ideation is neither in conflict with the perception nor isolated from it, but in logical continuity with it. This continuity must even be considered as the normal condition. We think in the direction of that which we perceive. The image seems to prepare the adaptation of the individual to his surroundings; it creates the foresight, the preparation of the means, and, in a word, everything which constitutes for us a final cause. Now, it is very necessary that the image appear real to be usefully the substitute of the sensation past or to come.

Let us establish one thing more. Acting as a substitute, the image not only appears as real as the sensation, it appears to be of the same nature; and the proof is that they are confounded one with the other, and that those who are not warned of the fact take one for the other. Every time a body is perceived, as I previously explained, there are images which affix themselves to the sensation unnoticed. We think we perceive when we are really remembering or imagining. This addition of the image to the sensation is not a petty and insignificant accessory; it forms the major part, perhaps nine-tenths, of perception. Hence arise the illusions of the senses, which are the result, not of sensations but of ideas. From this also comes the difficulty of knowing exactly what, under certain circumstances, is observation or perception, where the fact perceived ends, and where conjecture begins. Once acquainted with all these possibilities of errors, how can we suppose a radical separation between the sensation and the image?

Examined more closely, images appear to us to be divisible into as many kinds as sensations: visual images correspond to visual sensations, tactile to tactile, and so on with all the senses.

That which we experience in the form of sensation, we can experience over again in the form of image, and the repetition, generally weaker in intensity and poorer in details, may, under certain favourable circumstances, acquire an exceptional intensity, and even equal reality: as is shown by hallucinations. Here, certainly, are very sound reasons for acknowledging that the images which are at the bottom of our thoughts, and form the object of them, are the repetition, the modification, the transposition, the analysis or the synthesis of sensations experienced in the past, and possessing, in consequence, all the characteristics of bodily states. I believe that there is neither more nor less spirituality in the idea than in the sensation. That which forms its spirituality is the implied act of cognition; but its object is material.

I foresee a final objection: I shall be told that even when the unreality of the image is not the rule, and appears only under certain circumstances, it nevertheless exists. This is an important fact. It has been argued from the unreality of dreams and hallucinations in which we give a body to our ideas, that we do not in reality perceive external bodies, but simply psychical states and modifications of our souls. If our ideas consist—according to the hypothesis I uphold—in physical impressions which are felt, we shall be told that these particular impressions must participate in the nature of everything physical; that they are real, and always real; that they cannot be unreal, fictitious, and mendacious, and that, consequently, the fictitious character of ideation becomes inexplicable.

Two words of answer are necessary to this curious argument, which is nothing less than an effort to define the mental by the unreal, and to suppose that an appearance cannot be physical. No doubt, we say, every image, fantastical as it may seem as signification, is real in a certain sense, since it is the perception of a physical impression; but this physical nature of images does not prevent our making a distinction between true and false images. To take an analogous example: we are given a sheet of proofs to correct, we delete certain redundant letters, and, although they are printed with the same type as the other letters, we have the right to say they are false. Again, in a musical air, we may hear a false note, though it is as real as the others, since it has been played. This distinction between reality and truth ought to be likewise applied to mental images. All are real, but some are false. They are false when they do not accord with the whole reality; they are true when they agree; and every image is partly false because, being an image, it does not wholly accord with the actual perceptions. It creates a belief in a perception which does not occur; and by developing these ideas we could easily demonstrate how many degrees of falsehood there are.

Physiologically, we may very easily reconcile the falsity of the image with the physical character of the impression on which it is based. The image results from a partial cerebral excitement, which sensation results from an excitement which also acts upon the peripheral sensory nerves, and corresponds to an external object—an excitant which the image does not possess. This difference explains how it is that the image, while resulting from a physical impression, may yet be in a great number of cases declared false—that is to say, may be recognised as in contradiction to the perceptions.

To other minds, perhaps, metaphysical reasoning will be more satisfactory. For these, we propose to make a distinction between two notions, Existence or Reality, on the one hand, and Truth, on the other.

Existence or Reality is that of which we have an immediate apprehension. This apprehension occurs in several ways. In perception, in the first place. I perceive the reality of my body, of a table, the sky, the earth, in proportion to my perception of them. They exist, for if they did not, I could not perceive them. Another way of understanding reality is conception or thought. However much I may represent a thing to myself as imaginary, it nevertheless exists in a certain manner, since I can represent it to myself. I therefore, in this case, say that it is real or it exists. It is of course understood, that in these definitions I am going against the ordinary acceptation of the terms; I am taking the liberty of proposing new meanings. This reality is, then, perceived in one case and conceived in the other. Perceptibility or conceivability are, then, the two forms which reality may assume. But reality is not synonymous with truth; notwithstanding the custom to the contrary, we may well introduce a difference between these two terms. Reality is that which is perceived or conceived; truth is that which accords with the whole of our knowledge. Reality is a function of the senses or of ideation; truth is a function of reasoning or of the reason.

For cognition to be complete, it requires the aid of all these functions. And, in fact, what does conception by itself give? It allows us to see if a thing is capable of representation. This is not a common-place thing, I will observe in passing; for many things we name are not capable of representation, and there is often a criticism to be made; we think we are representing, and we are not. What is capable of representation exists as a representation, but is it true? Some philosophers have imagined so, but they are mistaken; what we succeed in conceiving is alone possible.

Let us now take the Perceptible. Is what one perceives true? Yes, in most cases it is so in fact; but an isolated perception may be false, and disturbed by illusions of all kinds. It is all very well to say, “I see, I touch.” There is no certainty through the senses alone in many circumstances that the truth has been grasped. If I am shown the spirit of a person I know to be dead, I shall not, notwithstanding the testimony of my eyes, believe it to be true, for this apparition would upset all my system of cognitions.

Truth is that which, being deemed conceivable, and being really perceived, has also the quality of finding its place, its relation, and its confirmation in the whole mass of cognitions previously acquired.

These distinctions,[3] if developed, would readily demonstrate that the advantages of observation are not eclipsed by those of speculation; and that those of speculation, in their turn, do not interfere with those of observation. But we have not time to develop these rules of logic; it will be sufficient to point out their relation to the question of the reality of mental images. Here are my conclusions in two words. Physical phenomena and images are always real, since they are perceived or conceived; what is sometimes wanting to them, and makes them false, is that they do not accord with the rest of our cognitions.[4]

Thus, then, are all objections overruled, in my opinion at least. We can now consider the world of ideas as a physical world; but it is one of a peculiar nature, which is not, like the other, accessible to all, and is subject to its own laws, which are laws of association. By these very different characteristics, it separates itself so sharply from the outer world that all endeavour to bring the two together seems shocking; and it is very easy to understand that many minds should wish to remain faithful to the conception that ideas form a mental or moral world. No metaphysical reasoning could prevail against this sentiment, and we must give up the idea of destroying it. But we think we have shown that idea, like sensation, comprises at the same time the physical and the mental.

  1. Let me say, in passing, that this separation that Descartes thinks he can establish between perception and ideation, is only conceivable on condition that it be not too closely examined, and that no exact definition of ideation be given. If we remark, in fact, that all thought is a reproduction, in some degree, of a sensation, we arrive at this conclusion: that a thought operated by a soul distinct from the body would be a thought completely void and without object, it would be the thought of nothingness. It is not, therefore, conceivable. Consequently the criterion, already so dangerous, which Descartes constantly employs—to wit: that what we clearly conceive is true—cannot apply to thought, if we take the trouble to analyse it and to replace a purely verbal conception by intuition.
  2. I somewhat regret that Taine fell into the common-place idea of the opposition of the brain and thought; he took up again this old idea without endeavouring to analyse it, and only made it his own by the ornamentation of his style. And as his was a mind of powerful systematisation, the error which he committed led him into much wider consequences than the error of a more common mind would have done.
  3. I have just come across them again in an ingenious note of C. L. Herrick: The Logical and Psychological Distinction between the True and the Real (Psych. Rev., May 1904). I entirely agree with this author. But it is not he who exercised a suggestion over my mind; it was M. Bergson. See Matière et Mémoire, p. 159.
  4. In order to remain brief, I have not thought fit to allude in the text to a question of metaphysics which closely depends on the one broached by me: the existence of an outer world. Philosophers who define sensation as a modality of our Ego are much embarrassed later in demonstrating the existence of an outer world. Having first admitted that our perception of it is illusory, since, when we think we perceive this world, we have simply the feeling of the modalities of our Ego, they find themselves powerless to demonstrate that this illusion corresponds to a truth, and invoke in despair, for the purpose of their demonstration, instinct, hallucination, or some a priori law of the mind. The position we have taken in the discussion is far more simple. Since every sensation is a fragment of matter perceived by a mind, the aggregate of sensations constitutes the aggregate of matter. There is in this no deceptive appearance, and consequently no need to prove a reality distinct from appearances. As to the argument drawn from dreams and hallucinations which might be brought against this, I have shown how it is set aside by a distinction between perceptibility and truth. It is no longer a matter of perception, but of reasoning. In other words, all that we see, even in dreams, is real, but is not in its due place.