Through thinking, concepts and ideas arise. What a concept is cannot be expressed in words. Words can do no more than draw our attention to the fact that we have concepts. When someone sees a tree, his thinking reacts to his observation, an ideal element is added to the object, and he considers the object and the ideal counterpart as belonging together. When the object disappears from his field of observation, only the ideal counterpart of it remains. This latter is the concept of the object. The more our range of experience is widened, the greater becomes the sum of our concepts. But concepts certainly do not stand isolated from one another. They combine to form a systematically ordered whole. The concept “organism”, for instance, links up with those of “orderly development” and “growth”. Other concepts which are based on single objects merge together into a unity. All concepts I may form of lions merge into the collective concept “lion”. In this way all the separate concepts combine to form a closed conceptual system in which each has its special place. Ideas do not differ qualitatively from concepts. They are but fuller, more saturated, more comprehensive concepts. I must attach special importance to the necessity of bearing in mind, here, that I make thinking my starting point, and not concepts and ideas which are first gained by means of thinking. For these latter already presuppose thinking. My remarks regarding the self-supporting and self-determined nature of thinking cannot, therefore, be simply transferred to concepts. (I make special mention of this, because it is here that I differ from Hegel, who regards the concept as something primary and original.)
Concepts cannot be gained through observation. This follows from the simple fact that the growing human being only slowly and gradually forms the concepts corresponding to the objects which surround him. Concepts are added to observation.
A philosopher widely read at the present day — Herbert Spencer — describes the mental process which we carry out with respect to observation as follows:
If, when walking through the fields some day in September, you hear a rustle a few yards in advance, and on observing the ditch-side where it occurs, see the herbage agitated, you will probably turn towards the spot to learn by what this sound and motion are produced. As you approach there flutters into the ditch a partridge; on seeing which your curiosity is satisfied — you have what you call an explanation of the appearances. The explanation, mark, amounts to this; that whereas throughout life you have had countless experiences of disturbance among small stationary bodies, accompanying the movement of other bodies among them, and have generalized the relation between such disturbances and such movements, you consider this particular disturbance explained on finding it to present an instance of the like relation. 1First Principles, Part I, 23.
A closer analysis shows matters to stand very differently from the way described above. When I hear a noise, I first look for the concept which fits this observation. It is this concept which first leads me beyond the mere noise. If one thinks no further, one simply hears the noise and is content to leave it at that. But my reflecting makes it clear to me that I have to regard the noise as an effect. Therefore not until I have connected the concept of effect with the perception of the noise, do I feel the need to go beyond the solitary observation and look for the cause. The concept of effect calls up that of cause, and my next step is to look for the object which is being the cause, which I find in the shape of the partridge. But these concepts, cause and effect, I can never gain through mere observation, however many instances the observation may cover. Observation evokes thinking, and it is thinking that first shows me how to link one separate experience to another.
If one demands of a “strictly objective science” that it should take its content from observation alone, then one must at the same time demand that it should forego all thinking. For thinking, by its very nature, goes beyond what is observed.
We must now pass from thinking to the being that thinks; for it is through the thinker that thinking is combined with observation. Human consciousness is the stage upon which concept and observation meet and become linked to one another. In saying this we have in fact characterized this (human) consciousness. It is the mediator between thinking and observation. In as far as we observe a thing it appears to us as given; in as far as we think, we appear to ourselves as being active. We regard the thing as object and ourselves as thinking subject. Because we direct our thinking upon our observation, we have consciousness of objects; because we direct it upon ourselves, we have consciousness of ourselves, or self-consciousness. Human consciousness must of necessity be at the same time self-consciousness because it is a consciousness which thinks. For when thinking contemplates its own activity, it makes its own essential being, as subject, into a thing, as object.
It must, however, not be overlooked that only with the help of thinking am I able to determine myself as subject and contrast myself with objects. Therefore thinking must never be regarded as a merely subjective activity. Thinking lies beyond subject and object. It produces these two concepts just as it produces all others. When, therefore, I, as thinking subject, refer a concept to an object, we must not regard this reference as something purely subjective. It is not the subject that makes the reference, but thinking. The subject does not think because it is a subject; rather it appears to itself as subject because it can think. The activity exercised by man as a thinking being is thus not merely subjective. Rather is it something neither subjective nor objective, that transcends both these concepts. I ought never to say that my individual subject thinks, but much more that my individual subject lives by the grace of thinking. Thinking is thus an element which leads me out beyond myself and connects me with the objects. But at the same time it separates me from them, inasmuch as it sets me, as subject, over against them.
It is just this which constitutes the double nature of man. He thinks, and thereby embraces both himself and the rest of the world. But at the same time it is by means of thinking that he determines himself as an individual confronting the things.
We must next ask ourselves how that other element, which we have so far simply called the object of observation and which meets the thinking in our consciousness, comes into our consciousness at all.
In order to answer this question we must eliminate from our field of observation everything that has been imported by thinking. For at any moment the content of our consciousness will already be interwoven with concepts in the most varied ways.
We must imagine that a being with fully developed human intelligence originates out of nothing and confronts the world. What it would be aware of, before it sets its thinking in motion, would be the pure content of observation. The world would then appear to this being as nothing but a mere disconnected aggregate of objects of sensation: colors, sounds, sensations of pressure, of warmth, of taste and smell; also feelings of pleasure and pain. This aggregate is the content of pure, unthinking observation. Over against it stands thinking, ready to begin its activity as soon as a point of attack presents itself. Experience shows at once that this does happen. Thinking is able to draw threads from one element of observation to another. It links definite concepts with these elements and thereby establishes a relationship between them. We have already seen how a noise which we hear becomes connected with another observation by our identifying the former as the effect of the latter.
If now we recollect that the activity of thinking is on no account to be considered as merely subjective, then we shall also not be tempted to believe that the relationships thus established by thinking have merely subjective validity.
Our next task is to discover by means of thoughtful reflection what relation the immediately given content of observation mentioned above has to the conscious subject.
The ambiguity of current speech makes it necessary for me to come to an agreement with my readers concerning the use of a word which I shall have to employ in what follows. I shall apply the word “percept” to the immediate objects of sensation enumerated above, in so far as the conscious subject apprehends them through observation. It is, then, not the process of observation but the object of observation which I call the “percept”.
I do not choose the term “sensation”, since this has a definite meaning in physiology which is narrower than that of my concept of “percept”. I can speak of a feeling in myself (emotion) as percept, but not as sensation in the physiological sense of the term. Even my feeling becomes known to me by becoming a percept for me. And the way in which we gain knowledge of our thinking through observation is such that thinking too, in its first appearance for our consciousness, may be called a percept.
The naïve man regards his percepts, such as they appear to his immediate apprehension, as things having an existence wholly independent of him. When he sees a tree he believes in the first instance that it stands in the form which he sees, with the colors of its various parts, and so on, there on the spot towards which his gaze is directed. When the same man sees the sun in the morning appear as a disc on the horizon, and follows the course of this disc, he believes that all this actually exists and happens just as he observes it. To this belief he clings until he meets with further percepts which contradict his former ones. The child who as yet has no experience of distance grasps at the moon, and only corrects its picture of the reality, based on first impressions, when a second percept contradicts the first. Every extension of the circle of my percepts compels me to correct my picture of the world. We see this in everyday life, as well as in the spiritual development of mankind. The picture which the ancients made for themselves of the relation of the earth to the sun and other heavenly bodies had to be replaced by another when Copernicus found that it was not in accordance with some percepts, which in those early days were unknown. A man who had been born blind said, when operated on by Dr. Franz, that the picture of the size of objects which he had formed by his sense of touch before his operation, was a very different one. He had to correct his tactual percepts by his visual percepts.
How is it that we are compelled to make these continual corrections to our observations?
A simple reflection gives the answer to this question. When I stand at one end of an avenue, the trees at the other end, away from me, seem smaller and nearer together than those where I stand. My percept-picture changes when I change the place from which I am looking. Therefore the form in which it presents itself to me is dependent on a condition which is due not to the object but to me, the perceiver. It is all the same to the avenue wherever I stand. But the picture I have of it depends essentially on just this viewpoint. In the same way, it makes no difference to the sun and the planetary system that human beings happen to look at them from the earth; but the percept-picture of the heavens presented to them is determined by the fact that they inhabit the earth. This dependence of our percept-picture on our place of observation is the easiest one to understand. The matter becomes more difficult when we realize how our world of percepts is dependent on our bodily and spiritual organization. The physicist shows us that within the space in which we hear a sound there are vibrations of the air, and also that the body in which we seek the origin of the sound exhibits a vibrating movement of its parts. We perceive this movement as sound only if we have a normally constructed ear. Without this the world would be for ever silent for us. Physiology tells us that there are people who perceive nothing of the magnificent splendor of color which surrounds us. Their percept-picture has only degrees of light and dark. Others are blind only to one color, for example, red. Their world picture lacks this hue, and hence it is actually a different one from that of the average man. I should like to call the dependence of my percept-picture on my place of observation, “mathematical”, and its dependence on my organization, “qualitative”. The former determines the proportions of size and mutual distances of my percepts, the latter their quality. The fact that I see a red surface as red — this qualitative determination — depends on the organization of my eye.
My percept-pictures, then, are in the first instance subjective. The recognition of the subjective character of our percepts may easily lead us to doubt whether there is any objective basis for them at all. When we realize that a percept, for example that of a red color or of a certain tone, is not possible without a specific structure of our organism, we may easily be led to believe that it has no permanency apart from our subjective organization and that, were it not for our act of perceiving it as an object, it would not exist in any sense. The classical representative of this view is George Berkeley, who held that from the moment we realize the importance of the subject for perception, we are no longer able to believe in the existence of a world without a conscious Spirit.
Some truths there are so near and obvious to the mind that man need only open his eyes to see them. Such I take this important one to be, to wit, that all the choir of heaven and furniture of the earth, in a word, all those bodies which compose the mighty frame of the world, have not any subsistence without a mind, that their being is to be perceived or known; that, consequently, so long as they are not actually perceived by me, or do not exist in my mind or that of any other created spirit, they must either have no existence at all, or else subsist in the mind of some Eternal Spirit. 2Berkeley Principles of Human Knowledge, Part I, Section 6.
On this view, when we take away the fact of its being perceived, nothing remains of the percept. There is no color when none is seen, no sound when none is heard. Extension, form, and motion exist as little as color and sound apart from the act of perception. Nowhere do we see bare extension or shape, but these are always bound up with color or some other quality unquestionably dependent upon our subjectivity. If these latter disappear when we cease to perceive them, then the former, being bound up with them, must disappear likewise.
To the objection that there must be things that exist apart from consciousness and to which the conscious percept-pictures are similar, even though figure, color, sound, and so on, have no existence except within the act of perceiving, the above view would answer that a color can be similar only to a color, a figure only to a figure. Our percepts can be similar only to our percepts and to nothing else. Even what we call an object is nothing but a collection of percepts which are connected in a particular way. If I strip a table of its shape, extension, color, etc. — in short, of all that is merely my percept — then nothing remains over. This view, followed up logically, leads to the assertion that the objects of my perceptions exist only through me, and indeed only in as far as, and as long as, I perceive them; they disappear with my perceiving and have no meaning apart from it. Apart from my percepts, I know of no objects and cannot know of any.
No objection can be made to this assertion as long as I am merely referring to the general fact that the percept is partly determined by the organization of myself as subject. The matter would appear very different if we were in a position to say just what part is played by our perceiving in the bringing forth of a percept. We should then know what happens to a percept while it is being perceived, and we should also be able to determine what character it must already possess before it comes to be perceived.
This leads us to turn our attention from the object of perception to the subject of perception. I perceive not only other things, but also myself. The percept of myself contains, to begin with, the fact that I am the stable element in contrast to the continual coming and going of the percept-pictures. The percept of my “I” can always come up in my consciousness while I am having other percepts. When I am absorbed in the perception of a given object I am for the time being aware only of this object. To this the percept of my self can be added. I am then conscious not only of the object but also of my own personality which confronts the object and observes it. I do not merely see a tree, but I also know that it is I who am seeing it. I know, moreover, that something happens in me while I am observing the tree. When the tree disappears from my field of vision, an after-effect of this process remains in my consciousness — a picture of the tree. This picture has become associated with my self during my observation. My self has become enriched; its content has absorbed a new element. This element I call my mental picture of the tree. I should never have occasion to speak of mental pictures did I not experience them in the percept of my own self. Percepts would come and go; I should let them slip by. Only because I perceive my self, and observe that with each percept the content of my self, too, is changed, am I compelled to connect the observation of the object with the changes in my own condition, and to speak of my mental picture.
I perceive the mental picture in my self in the same sense as I perceive color, sound, etc., in other objects. I am now also able to distinguish these other objects that confront me, by calling them the outer world, whereas the content of my percept of my self I call my inner world. The failure to recognize the true relationship between mental picture and object has led to the greatest misunderstandings in modern philosophy. The perception of a change in me, the modification my self undergoes, has been thrust into the foreground, while the object which causes this modification is lost sight of altogether. It has been said that we perceive not objects but only our mental pictures. I know, so it is said, nothing of the table in itself, which is the object of my observation, but only of the change which occurs within me while I am perceiving the table. This view should not be confused with the Berkeleyan theory mentioned above. Berkeley maintains the subjective nature of the content of my percepts, but he does not say that my knowledge is limited to my mental pictures. He limits my knowledge to my mental pictures because, in his opinion, there are no objects apart from mental picturing. What I take to be a table no longer exists, according to Berkeley, when I cease to look at it. This is why Berkeley holds that my percepts arise directly through the omnipotence of God. I see a table because God calls up this percept in me. For Berkeley, therefore, there are no real beings other than God and human spirits. What we call the “world” exists only in these spirits. What the naïve man calls the outer world, or corporeal nature, is for Berkeley non-existent. This theory is confronted by the now predominant Kantian view which limits our knowledge of the world to our mental pictures, not because it is convinced that things cannot exist beyond these mental pictures, but because it believes us to be so organized that we can experience only the changes of our own selves, but not the things-in-themselves that cause these changes. This view concludes from the fact that I know only my mental pictures, not that there is no reality independent of them, but only that the subject cannot directly assimilate such reality. The subject can merely, “through the medium of its subjective thoughts, imagine it, invent it, think it, cognize it, or perhaps even fail to cognize it.” 3O. Liebmann, Zur Analysis der Wirklichkeit, p 28. This (Kantian) conception believes it gives expression to something absolutely certain, something which is immediately evident, requiring no proof.
The first fundamental proposition which the philosopher must bring to clear consciousness is the recognition that our knowledge, to begin with, is limited to our mental pictures. Our mental pictures are the only things that we know directly, experience directly; and just because we have direct experience of them, even the most radical doubt cannot rob us of our knowledge of them. On the other hand, the knowledge which goes beyond my mental pictures — taking mental pictures here in the widest possible sense, so as to include all psychical processes — is not proof against doubt. Hence, at the very beginning of all philosophizing we must explicitly set down all knowledge which goes beyond mental pictures as being open to doubt.
These are the opening sentences of Volkelt's book on Immanuel Kant's Theory of Knowledge. What is here put forward as an immediate and self-evident truth is in reality the result of a thought operation which runs as follows: The naïve man believes that things, just as we perceive them, exist also outside our consciousness. Physics, physiology, and psychology, however, seem to teach us that for our percepts our organization is necessary, and that therefore we cannot know anything about external objects except what our organization transmits to us. Our percepts are thus modifications of our organization, not things-in-themselves. This train of thought has in fact been characterized by Eduard von Hartmann as the one which must lead to the conviction that we can have direct knowledge only of our mental pictures. 4See his Das Grundproblem der Erkenntnistheorie, pp. 16–40. Because, outside our organism, we find vibrations of physical bodies and of the air which are perceived by us as sound, it is concluded that what we call sound is nothing more than a subjective reaction of our organism to these motions in the external world. Similarly, it is concluded that color and warmth are merely modifications of our organism. And, further, these two kinds of percepts are held to be produced in us through processes in the external world which are utterly different from what we experience as warmth or as color. When these processes stimulate the nerves in my skin, I have the subjective percept of warmth; when they stimulate the optic nerve, I perceive light and color. Light, color, and warmth, then, are the responses of my sensory nerves to external stimuli. Even the sense of touch reveals to me, not the objects of the outer world, but only states of my own body. In the sense of modern physics one could somehow think that bodies consist of infinitely small particles called molecules, and that these molecules are not in direct contact, but are at certain distances from one another. Between them, therefore, is empty space. Across this space they act on one another by forces of attraction and repulsion. If I put my hand on a body, the molecules of my hand by no means touch those of the body directly, but there remains a certain distance between body and hand, and what I experience as the body's resistance is nothing but the effect of the force of repulsion which its molecules exert on my hand. I am absolutely external to the body and perceive only its effects on my organism.
In amplification of this discussion, there is the theory of the so-called Specific Nerve Energies, advanced by J. Müller (1801–1858). It asserts that each sense has the peculiarity that it responds to all external stimuli in one particular way only. If the optic nerve is stimulated, perception of light results, irrespective of whether the stimulation is due to what we call light, or whether mechanical pressure or an electric current works upon the nerve. On the other hand, the same external stimulus applied to different senses gives rise to different percepts. The conclusion from these facts seems to be that our senses can transmit only what occurs in themselves, but nothing of the external world. They determine our percepts, each according to its own nature.
Physiology shows that there can be no direct knowledge even of the effects which objects produce on our sense organs. Through following up the processes which occur in our own bodies, the physiologist finds that, even in the sense organs, the effects of the external movement are transformed in the most manifold ways. We can see this most clearly in the case of eye and ear. Both are very complicated organs which modify the external stimulus considerably before they conduct it to the corresponding nerve. From the peripheral end of the nerve the already modified stimulus is then conducted to the brain. Only now can the central organs be stimulated. Therefore it is concluded that the external process undergoes a series of transformations before it reaches consciousness. What goes on in the brain is connected by so many intermediate links with the external process, that any similarity to the latter is out of the question. What the brain ultimately transmits to the soul is neither external processes, nor processes in the sense organs, but only such as occur in the brain. But even these are not perceived directly by the soul. What we finally have in consciousness are not brain processes at all, but sensations. My sensation of red has absolutely no similarity to the process which occurs in the brain when I sense red. The redness, again, only appears as an effect in the soul, and the brain process is merely its cause. This is why Hartmann says, “What the subject perceives, therefore, are always only modifications of his own psychical states and nothing else.” 5Das Grundproblem der Erkenntnistheorie, pp. 37. When I have the sensations, however, they are as yet very far from being grouped into what I perceive as “things”. Only single sensations can be transmitted to me by the brain. The sensations of hardness and softness are transmitted to me by the sense of touch, those of color and light by the sense of sight. Yet all these are to be found united in one and the same object. This unification, therefore, can only be brought about by the soul itself; that is, the soul combines the separate sensations, mediated through the brain, into bodies. My brain conveys to me singly, and by widely different paths, the visual, tactile, and auditory sensations which the soul then combines into the mental picture of a trumpet. It is just this very last link in a process (the mental picture of the trumpet) which for my consciousness is the very first thing that is given. In it nothing can any longer be found of what exists outside me and originally made an impression on my senses. The external object has been entirely lost on the way to the brain and through the brain to the soul.
It would be hard to find in the history of human culture another edifice of thought which has been built up with greater ingenuity, and which yet, on closer analysis, collapses into nothing. Let us look a little closer at the way it has been constructed. One starts with what is given in naïve consciousness, with the thing as perceived. Then one shows that none of the qualities which we find in this thing would exist for us had we no sense organs. No eye — no color. Therefore the color is not yet present in that which affects the eye. It arises first through the interaction of the eye and the object. The latter is, therefore, colorless. But neither is the color in the eye, for in the eye there is only a chemical or physical process which is first conducted by the optic nerve to the brain, and there initiates another process. Even this is not yet the color. That is only produced in the soul by means of the brain process. Even then it does not yet enter my consciousness, but is first transferred by the soul to a body in the external world. There, upon this body, I finally believe myself to perceive it. We have traveled in a complete circle. We became conscious of a colored body. That is the first thing. Here the thought operation starts. If I had no eye, the body would be, for me, colorless. I cannot therefore attribute the color to the body. I start on the search for it. I look for it in the eye — in vain; in the nerve — in vain; in the brain — in vain once more; in the soul — here I find it indeed, but not attached to the body. I find the colored body again only on returning to my starting point. The circle is completed. I believe that I am cognizing as a product of my soul that which the naïve man regards as existing outside him, in space.
As long as one stops here everything seems to fit beautifully. But we must go over the whole thing again from the beginning. Hitherto I have been dealing with something — the external percept — of which, from my naïve standpoint, I have had until now a totally wrong conception. I thought that the percept, just as I perceive it, had objective existence. But now I observe that it disappears together with my mental picture, that it is only a modification of my inner state of soul. Have I, then, any right at all to start from it in my arguments? Can I say of it that it acts on my soul? I must henceforth treat the table, of which formerly I believed that it acted on me and produced a mental picture of itself in me, as itself a mental picture. But from this it follows logically that my sense organs and the processes in them are also merely subjective. I have no right to speak of a real eye but only of my mental picture of the eye. Exactly the same is true of the nerve paths, and the brain process, and no less of the process in the soul itself, through which things are supposed to be built up out of the chaos of manifold sensations. If, assuming the truth of the first circle of argumentation, I run through the steps of my act of cognition once more, the latter reveals itself as a tissue of mental pictures which, as such, cannot act on one another. I cannot say that my mental picture of the object acts on my mental picture of the eye, and that from this interaction my mental picture of color results. Nor is it necessary that I should say this. For as soon as I see clearly that my sense organs and their activity, my nerve and soul processes, can also be known to me only through perception, the train of thought which I have outlined reveals itself in its full absurdity. It is quite true that I can have no percept without the corresponding sense organ. But just as little can I be aware of a sense organ without perception. From the percept of a table I can pass to the eye which sees it, or the nerves in the skin which touch it, but what takes place in these I can, in turn, learn only from perception. And then I soon notice that there is no trace of similarity between the process which takes place in the eye and the color which I perceive. I cannot eliminate my color percept by pointing to the process which takes place in the eye during this perception. No more can I rediscover the color in the nerve or brain processes. I only add new percepts, localized within the organism, to the first percept, which the naïve man localizes outside his organism. I merely pass from one percept to another.
Moreover there is a gap in the whole argument. I can follow the processes in my organism up to those in my brain, even though my assumptions become more and more hypothetical as I approach the central processes of the brain. The path of external observation ceases with the process in my brain, more particularly with the process which I should observe if I could deal with the brain using the instruments and methods of physics and chemistry. The path of inner observation begins with the sensation, and continues up to the building of things out of the material of sensation. At the point of transition from brain process to sensation, the path of observation is interrupted.
The way of thinking here described, known as critical idealism, in contrast to the standpoint of naïve consciousness known as naïve realism, makes the mistake of characterizing the one percept as mental picture while taking the other in the very same sense as does the naïve realism which it apparently refutes. It wants to prove that percepts have the character of mental pictures by naïvely accepting the percepts connected with one's own organism as objectively valid facts; and over and above this, it fails to see that it confuses two spheres of observation, between which it can find no connection.
Critical idealism can refute naïve realism only by itself assuming, in naïve-realistic fashion, that one's own organism has objective existence. As soon as the idealist realizes that the percepts connected with his own organism are exactly of the same nature as those which naïve realism assumes to have objective existence, he can no longer use those percepts as a safe foundation for his theory. He would have to regard even his own subjective organization as a mere complex of mental pictures. But this removes the possibility of regarding the content of the perceived world as a product of our spiritual organization. One would have to assume that the mental picture “color” was only a modification of the mental picture “eye”. So-called critical idealism cannot be proved without borrowing from naïve realism. Naive realism can be refuted only if, in another sphere, its own assumptions are accepted without proof as being valid.
This much, then, is certain: Investigation within the world of percepts cannot establish critical idealism, and consequently, cannot strip percepts of their objective character.
Still less can the principle “the perceived world is my mental picture” be claimed as obvious and needing no proof. Schopenhauer begins his chief work 6Die Welt als Wille und Vorstellung. with the words:
The world is my mental picture — this is a truth which holds good for everything that lives and cognizes, though man alone can bring it into reflective and abstract consciousness. If he really does this, he has attained to philosophical discretion. It then becomes clear and certain to him that he knows no sun and no earth, but only an eye that sees a sun, a hand that feels an earth; that the world which surrounds him is there only as mental picture, that is, only in relation to something else, to the one who pictures it, which is he himself. If any truth can be asserted a priori, it is this one, for it is the expression of that form of all possible and thinkable experience which is more universal than all others, than time, space, or causality, for all these presuppose it ...
This whole theory is wrecked by the fact, already mentioned, that the eye and the hand are percepts no less than the sun and the earth. Using Schopenhauer's expressions in his own sense, we could reply: My eye that sees the sun, my hand that feels the earth, are my mental pictures just as much as the sun and the earth themselves. That with this the whole theory cancels itself, is clear without further argument. For only my real eye and my real hand could have the mental pictures “sun” and “earth” as modifications of themselves; the mental pictures “eye” and “hand” cannot have them. Yet it is only of these mental pictures that critical idealism is allowed to speak.
Critical idealism is totally unfitted to form an opinion about the relationship between percept and mental picture. It cannot begin to make the distinction, mentioned above, between what happens to the percept in the process of perception and what must be inherent in it prior to perception. We must, therefore, tackle this problem in another way.