Through thinking, concepts and ideas arise. What a concept is cannot be said in words. Words can only make the human being aware of the fact that he has concepts. When someone sees a tree, his thinking reacts to his observation; to the object there comes then an ideal counterpart, and he regards the object and ideal counterpart as belonging together. When the object disappears from his field of observation, there remains behind only its ideal counterpart. The latter is the concept of the object. The more our experience broadens, the greater the sum of our concepts becomes. The concepts however by no means stand there isolated. They join themselves together into a lawful whole. The concept “organism” joins itself, for example, to the others of “lawful development” and “growth.” Other concepts formed in connection with single things merge totally into one. All the concepts that I make for myself of lions merge together into the overall concept “lion.” In this way the individual concept join themselves into a united system of concepts within which every one has its particular place. Ideas are not qualitatively different from concepts. They are only concepts that are fuller in content, more saturated, and wider in scope. I must particularly emphasize that heed be taken at this point of the fact that I have indicated thinking as my starting point and not concepts and ideas, which are first gained through thinking. These already presuppose thinking. What I have said therefore about the self-sustaining and self-determined nature of thinking cannot simply be transferred to concepts. (I state this here expressly, because herein lies my difference with Hegel. He posits the concept as primary and original.)
The concept cannot be gained from observation. This is already evident from the fact that the maturing human being only slowly and gradually forms his concepts for the objects which surround him. The concepts are added to the observation.
A widely read philosopher of the present day, Herbert Spencer, describes the mental process we carry out with respect to an observation in the following way:
“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 toward 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 through 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, Par. 23. When viewed more closely the matter turns out to be completely different from what is described here. When I hear a sound, I seek first of all the concept corresponding to this observation. It is only this concept that first takes me beyond the sound. Whoever does not reflect further just hears the sound and is content with that. Through my reflection, however, it is clear to me that I have to comprehend a sound as an effect. Therefore, only when I join the concept effect with the perception of the sound, am I moved to go beyond the individual observation and seek the cause. The concept “effect” calls up the concept “cause,” and I then look for the causal object, which I find in the form of the partridge. These concepts, “cause” and “effect,” however, I can never gain through mere observation, no matter how many instances it may cover. Observation calls forth thinking, and this latter first shows me the way to join the single experience to another.
If one demands of a “strictly objective science” that is take its content only from observation, one must demand at the same time that it renounce all thinking Because thinking by its very nature goes beyond what is observed.
This is the place now to pass from thinking to the being who thinks. For, through him thinking is joined with observation. Human consciousness is the stage upon which concept and observation meet each other and where they become joined. But this (human) consciousness is thereby characterized at the same time. It is the mediator between thinking and observation. Insofar as the human being observes a thing, this thing appears to him as given; insofar as he thinks, he appears to himself as active. He considers the thing as object, himself as the thinking subject. Because he focuses his thinking upon the observation, he has consciousness of the objects; because he directs his thinking upon himself, he has consciousness of himself or self-consciousness. Human consciousness must necessarily be self-consciousness at the same time, because it is thinking consciousness. For then thinking directs its gaze upon its own activity, it then has its own inmost being, its subject, as object before it.
But the fact must not be overlooked now that it is only with the help of thinking that we are able to designate ourselves as subject ad to set ourselves over against objects. Therefore thinking must never be considered to be a merely subjective activity. Thinking is beyond subject and object. It forms these two concepts just as much as all others. When we as thinking subject, therefore, relate the concept to an object, we must not, in so doing, consider this relationship to be something merely subjective. It is not the subject that brings about the relationship, but rather thinking. The subject does not think by virtue of being subject, but rather appears to itself as a subject because it is able to think. The activity which the human being as thinking entity, exercises is therefore no merely subjective one, but rather one that is neither subjective nor objective, one that goes beyond these two concepts. I must never say that my individual subject thinks; it is much more the case that my subject itself lives by the grace of thinking. Thinking is an element that leads me out of and above my self, and joins me with objects. But it separates me from them at the same time, inasmuch as it places me over against them a subject.
This is the basis for the double nature of the human being: he thinks and thereby encompasses himself and the rest of the world; but he must, by means of thinking, at the same time designate himself as an individual that stands over and against the things.
The next thing will now be to ask ourselves how the other element — which we have up to now merely called object of observation, and which encounters thinking within our consciousness — come into our consciousness?
In order to answer this question we must exclude from our field of observation everything that has already been brought into it through thinking. For our content of consciousness at any given moment is already permeated with concepts in the most manifold way.
We must picture to ourselves a being with fully developed human intelligence arising out of nothingness and approaching the world. What he would become aware of in it, before he brought his thinking into activity, is the pure content of observation. The world would then show this being only the bare aggregate, without interconnection of the objects of sensation: colors, tones, sensations of pressure, warmth, taste, and smell; then feelings of pleasure and displeasure. This aggregate is the content of pure observation without thoughts. Over against it stands thinking, which is ready to unfold its activity when a point of attack is found. Experience soon teaches us that a point is found. Thinking is capable of drawing threads from one element of observation to the other. Thinking connects definite concepts with these elements and brings them thereby into a relationship. We have already seen above, how a sound confronting us is joined with another observation through the fact that we designate the former as the effect of the latter.
When we now recall that the activity of thinking is absolutely not to be taken as subjective, we will thus also not be tempted to believe that such connections, established through thinking, have a merely subjective validity.
It will now be a matter, through thinking considerations of seeking the connection which the directly given content of observation described above has to our conscious subject.
Because of the variability in the use of language it seems advisable for me to come to an understanding with my reader about the use of a word which I will have to employ in what follows. I will call the immediate objects of sensation enumerated above perceptions, insofar as the conscious subject takes cognizance of them through observation. I therefore use this word to indicate, not the process of observation, but rather the object of this observation.
I do not choose the term sensation, because in physiology this has a definite meaning that is narrower than my concept of perception. An emotion within myself can certainly be called a perception, but not a sensation in the physiological sense. I come to know even my emotions through their becoming perceptions for me. And the way we come to know our thinking through observation is such, that we can also use the word perception for thinking as it first appears to our consciousness.
The naive person considers his perceptions, in the way they immediately appear to him, as things having an existence completely independent of him. When he sees a tree, he believes right away that it is standing there in that spot toward which his gaze is directed, in the shape he sees, with the colors its parts have, etc. When the same person sees the sun appear in the morning as a disk on the horizon, and follows the course of this disk, he believes that all this exists and occurs in this way (in and for itself), just as he observes it to. He holds fast to his belief, until he meets other perceptions that contradict his former ones. The child, who does not yet have any experience of distance, reaches for the moon, and corrects the way he had first seen it to be only when a second perception is found to be in contradiction with the first. Every broadening of the circle of my perception obliges me to correct my picture of the world. This is evident in daily life just as much as in the spiritual development of mankind. The picture which the ancients made for themselves of the relationship of the earth to the sun and to the other heavenly bodies, had to be replaced by Copernicus with another one, because it did not accord with perceptions unknown to earlier times. A man born blind said, after Dr. Franz had operated on him, that before his operation he had formed a completely different picture of the size of objects through the perceptions of his sense of touch. He had to correct his perceptions of touch through his perceptions of sight.
How is it that we are compelled to make such continuous corrections of our observations?
A simple reflection brings the answer to this question. When I am standing at one end of an avenue of trees, the trees distant from me at the other end appear to me smaller and closer together than they do where I am standing. My perceptual picture becomes a different one when I change the place from which I make my observations. This picture, therefore, in the form in which it approaches me, is dependent upon a determining factor which is not due to the object, but which rather is attributable to me, the one doing the perceiving. For an avenue of trees it is a matter of complete indifference where I am standing. The picture, however, that I receive of it, is essentially dependent upon where I am standing. In the same way it is a matter of indifference to the sun and to the planetary system that human beings happen to view them from the earth. The perceptual picture, however, which presents itself to human beings is determined through this their dwelling place. This dependency of our perceptual picture upon our point of observation is the one that is easiest to recognize. The matter becomes more difficult, to be sure, when we learn to know the dependency of our perceptual world upon our bodily and spiritual organization. The physicist shows us that within the space in which we hear a sound, vibrations of the air take place, and that the body also, in which we seek the origin of the sound, exhibits a vibrating movement of its parts. We only perceive this movement as sound if we have a normally organized ear. Without such an ear the whole world would remain forever silent for us. Physiology teaches us that there are people who perceive nothing of the magnificent splendor of color that surrounds us. Their perceptual picture evinces only nuances of light and dark. Others do not perceive only one particular color, such as red, for example. This shade is missing from their world picture, which is therefore actually a different one than that of the average person. I would like to call the dependency of my perceptual picture upon my place of observation, “mathematical,” and the dependency upon my organization “qualitative.” Through the former, the size relationships and respective distances of my perceptions are determined; through the latter, the quality of my perceptions. That I see a red surface as red — this qualitative determination — depends upon the organization of my eye.
My perceptual pictures are therefore at first subjective. Knowledge of the subjective character of our perceptions can easily lead to doubt as to whether anything objective underlies them at all. When we know that a perception — of a red color, for example, or of a particular tone — is not possible without a definite structure in our organism, one can arrive at the belief that this perception, apart from our subjective organism, has no reality, that the perception has no kind of existence without the act of perceiving, whose object it is. This view has found a classic proponent in George Berkeley, who was of the opinion that the human being, from the moment he has become conscious of the significance of the subject for the perception, can no longer believe in a world that is present without the conscious mind. He says, “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 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.” 2Principles of Human Knowledge, Part I, Section 6 For this view, nothing more of the perception remains, if one disregards the fact of its being perceived. There is no color when none is seen, no tone when none is heard. Just as little as color and tone, do dimension, shape, and motion exist outside of the act of perception. We nowhere see bare dimension or shape, but always see them connected with color or with other characteristics which indisputably depend upon our subjectivity. If these latter characteristics disappear along with our perception, then that must also be the case for the elements of dimension or shape that are bound to them.
An objection can be made that, even if figure, color, tone, etc. do have not existence other than within my act of perception, there must still be things which are there without my act of perception, there must still be things which are there without my consciousness and to which my conscious perceptual pictures are similar; to this objection the above view responds by saying that a color can only be similar to a color, a figure similar to a figure. Our perceptions can only be similar to our perceptions, but not to any other things. Even what we call an object is nothing other than a group of perceptions which are connected in a definite way. If I take away from a table its shape, dimensions, color, etc. — everything in short that is only my perception — then nothing more remains. This view, consistently pursued, leads to the opinion that the objects of my perceptions are present only through me, and indeed only insofar as, and as long as, I perceive them; they disappear along with my act of perceiving and have no meaning without it. Other than my perceptions I know of no objects, however, and can know of none.
No objection can be brought against this opinion as long as I am merely bringing into consideration in a general way the fact that the perception is codetermined by the organization of my subject. The matter would present itself in an essentially different way, however, if we were able to say what the function of our perceiving is in the genesis of a perception. We would then know what is happening with the perception during the act of perceiving, and could also determine what about it would already have to exist, before it is perceived.
With this, our consideration of the object of perception leads over to the subject of perception. I do not perceive other things only; I also perceive my self. The perception of my self has at first the content that I am what endures in the face of perceptual pictures that continually come and go. The perception of my “I” can always appear in my consciousness while I am having other perceptions. When I am absorbed in the perception of a given object, I have for the moment only a consciousness of it. To this can then come the perception of my self. I am from then on conscious not merely of the object, but also of my personality, which stands before the object and observes it. I do not merely see a tree, but I also know that it is I who see it. I recognize also that something is occurring within me while I observe the tree. When the tree disappears from my field of vision, something of this occurrence remains behind for my consciousness: a picture of the tree. During my observation this picture has connected itself with my self. My self has become richer; its content has acquired a new element. This element I call my mental picture 3Vorstellung (often translated “representation”) of the tree. I would never be in a position to speak of mental pictures, if I did not experience them within the perception of my self. Perceptions would come and go; I would let them pass before me. Only because I perceive my self and notice that its content also changes with ever perception, do I see myself compelled to bring my observation of the object into relationship with my own change in condition, and to speak of my mental picture.
I perceive the mental picture connected to my self in the same sense as I perceive color, tone, etc. connected to other objects. I can also now make the distinction of calling these other objects which come before me outer world, while I designate the content of my self-perception as inner world. Misconceptions about the relationship of mental picture and object have brought about the greatest misunderstandings in modern philosophy. The perception of a change in us, the modification that my self undergoes, was pushed into the foreground, and the object causing this modification was totally lost from view. One said that we do not perceive the objects, but only our mental pictures. I supposedly know nothing about the table-in-itself, which is the object of my observation, but only about the change which takes place with my self while I am perceiving the table. This view should not be confused with that of Berkeley mentioned before. Berkeley maintains the subjective nature of the content of my perception, but he does not say I can only know about my mental pictures. He limits my knowledge to my mental pictures, because he is of the opinion that there are no objects outside of mental picturing. What I look upon as a table is for Berkeley no longer present as soon as I no longer direct my gaze upon it. Therefore Berkeley lets my perception arise directly through the power of God. I see a table because God calls forth this perception within me. Berkeley thus knows no other real beings except God and human spirits. What we call world is present only within spirits. What the naive person calls outer world, physical nature, does not exist for Berkeley. Over against this view there stands the Kantian one now predominating, which limits our knowledge of the world to our mental pictures, not because it is convinced that there can be nothing apart from our mental pictures, but because it believes us to be so organized that we can experience only the changes of our own self and not the things-in-themselves which cause these changes. From the fact that I know only my mental pictures, this view concludes not that there is no existence independent of these mental pictures, but only that the subject cannot take up such an existence directly into itself; it can do nothing with it except through the “medium of his subjective thoughts, to imagine it, to suppose it, to think it, to know it, or perhaps also not to know is” (O. Liebmann, Contribution to the Analysis of Reality). 4Zur Analysis der Wirklichkeit This view believes it is saying something absolutely certain, something directly obvious without any proof. “The first fundamental principle which the philosopher has to bring to distinct consciousness for himself consists in the recognition that our knowledge at first extends itself to nothing beyond our mental pictures. Our mental pictures are the only thing that we know directly, experience directly; and, just because we experience them directly, it is the case that even the most radical doubt cannot tear away from us our knowledge of our mental pictures. On the other hand, knowledge that goes beyond our mental picturing — whenever I use this expression I mean it in the widest sense, so that all psychic happenings come under it — is not secure from doubt. Therefore, at the beginning of any philosophizing, all knowledge which goes beyond our mental pictures must be expressly presented as doubtful”; thus Volkelt begins his book on Immanuel Kant's Epistemology. What is here presented in this way, as though it were an immediate and obvious truth, is in reality, however, the result of a thought-operation that runs as follows: The naive person believes that the objects, in the way he perceives them, are also present outside of his consciousness. Physics, physiology, and psychology seem to teach, however, that for our perceptions our organization is necessary, that we consequently can know about nothing except what our organization transmits to us from the things. Our perceptions are thus modifications of our organization, not things-in-themselves. Eduard von Hartmann has characterized the train of thought indicated here as in fact the one which must convince us of the principle that we can have a direct knowledge only of our mental pictures (see his Basic Problem of Epistemology). 5Das Grundproblem der Erkenntnistheorie Because outside of our organism, we find vibrations of physical bodies and of the air which manifest to us as sound, it is concluded that what we call sound is nothing more than a subjective reaction of our organism to those motions in the outer world. In the same way one finds that color and warmth are only modifications of our organism. And one is in fact of the view that these two kinds of perceptions are called forth in us through the effect of occurrences in the outer world which are utterly different form what our warmth of color experience is. When such occurrences stimulate the nerves in my skin, I have the subjective perception of warmth; when such occurrences encounter the optic nerve, I perceive light and color. Light, color, and warmth, therefore, are that with which my sensory nerves respond to the stimuli from outside. Even my sense of touch transmits to me, not the objects of the outer world, but only my own states. In the sense of modern physics one could think, for example, that bodies consist of infinitely small particles, of molecules, and that these molecules do not border directly upon each other, but rather are at certain distances from each other. Between them, therefore, is empty space. Across these distances the molecules act upon each other by means of forces of attraction and repulsion. When I bring my hand toward a body, the molecules of my hand by no means directly touch those of the body, but rather there remains a certain distance between body and hand; and what I sense as the body's resistance is nothing more than the effect of the force of repulsion which its molecules exert upon my hand. I am altogether outside the body and only perceive its effect upon my organism.
The doctrine put forward by J. Müller (1801–1858) about the so-called specific sense energies complements these reflections. It consists in declaring that each sense organ has the characteristic of responding to all outer stimuli in one specific way only. If the optic nerve is acted upon, a perception of light arises, no matter whether the stimulus occurs through what we call light, or whether a mechanical pressure or an electric current affects the nerve. Furthermore, different perceptions are called forth in the different sense organs by the same outer stimuli. This seems to indicate that our senses can transmit only what occurs within them, but nothing of the outer world. The senses, each according to its nature, determine the perceptions.
Physiology shows that a direct knowledge of what the objects cause to happen within our sense organs is also out of the question. As the physiologist pursues the occurrences in our own body, he finds that, already in the sense organs, the effects of an outer motion are transformed in the most manifold way. We see that most distinctly with the eye and ear. Both are very complicated organs which essentially change the outer stimulus before they bring it to the corresponding nerve. From the peripheral end of the nerve, the already changed stimulus is now conducted further to the brain. Here first of all the central organs must be stimulated again. From this is inferred that the outer occurrence has undergone a series of transformations before it comes to consciousness. What takes place in the brain is connected with the outer occurrence through so many intermediary occurrences that any similarity between the two is inconceivable. What the brain finally communicates to the soul are neither outer occurrences nor occurrences in the sense organs, but only such as are in the brain. But the soul still does not perceive even these directly. What we finally have in our consciousness are not brain processes at all, but rather sensations. My sensation of red has absolutely no similarity to the process which takes place in my brain when I experience the red. The latter only appears again in the soul as an effect and is only caused by the brain process. Therefore Hartmann says (The Basic Problem of Epistemology), “What the subject perceives are therefore always only modifications of his own psychic states and nothing else.” When I have sensations thee are, however, still far from being grouped together into what I perceive as the things. Only single sensations, after all, can be communicated to me through the brain. The sensations of hard and soft are communicated to me through the sense of touch, sensations of color and light through the sense of sight. In spite of this the sensations find themselves united upon one and the same object. This union must therefore first be accomplished by the soul itself. This means that the soul assembles into physical objects the single sensations communicated through the brain. My brain transmits to me individually my sensations of sight, touch, and hearing — and does this, indeed, along entirely different paths — which my soul then assembles into the mental picture “trumpet.” It is this last part (mental picture of the trumpet) of a process that, for my consciousness, is given first of all. There is in this lat part nothing more to be found of what is outside me and originally made an impression on my senses. The external object, on its way to the brain, and through the brain to the soul, has been entirely lost.
It would be difficult to find another edifice of thought in the history of the spiritual life of man which has been assembled with keener thought, and which nevertheless crumbles into nothingness upon closer examination. Let us take a closer look at the way it is built up. One starts first of all with what is given to naive consciousness, with the thing that is perceived. Then one shows that everything belonging to this thing would not be there for us if we had no senses. No eye: no color. Therefore the color is not yet present in that which works upon the eye. The color first arises through the interaction of the eye with the object. The latter is therefore colorless. But the color is also not present in the eye; for in it a chemical or physical process is present, which is first led to the brain through a nerve, and which there causes another process. Even this is not yet the color. The color is first called forth, through the brain process, within the soul. There the color still does not enter into my consciousness, but rather is first transferred outward by the soul onto a body. On this body I believe I finally perceive the color. We have made a complete circle. We become conscious of a colored body. That is first. Now the thought operation commences. If I had no eye, the body would be colorless for me. Thus, I cannot attribute the color to the body. I take up the search for the color. I look for it in the eye: in vain; in the nerve: in vain; in the brain: also in vain; in the soul: here I do find it, in fact, but not connected with the body. I find the colored body again only where I took my start. The circle is closed. I believe that I now recognize as a creation of my soul, what the naive person believes to be present outside of space.
As long as one stops here, everything seems to be in excellent shape. But the matter must be taken up once more from the beginning. Until now I have been dealing with an object: with the outer perception about which earlier, as a naive person, I had a completely incorrect view. I was of the opinion that the perception had an objective existence, in the form that I perceive it. Now I notice that the perception disappears along with my mental picturing, that it is only a modification of my soul state. Now do I still have any right at all to start with the perception in my consideration? Can I say of the perception that it acts upon my soul? From now on I must treat the table, which I earlier believed acted upon me and brought forth a mental picture of itself in me, itself as a mental picture. But then 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 an eye. It is just the same with the nerves and the brain process, and no less so with the occurrence in the soul itself through which things are supposedly built up out of the chaos of manifold sensations. If, under the assumption of the correctness of the first circle of thought, I run through once more the parts of my act of knowledge, the latter shows itself to be a web of mental pictures that, as such, certainly cannot act upon each other. I cannot say that my mental picture of the object acts upon my mental picture of the eye and that out of this interaction emerges my mental picture of the color. But I also do not need to do this. For as soon as it is clear to me that my sense organs and their activity, my nerve and soul process, can also only be given me through perception, the train of thought described above reveals itself in its full impossibility. It is correct that for me there is no perception without the corresponding sense organ. But just as little is there a sense organ without perception. I can go over from my perception of the table to the eye that sees it, to the nerves of the hand which touch it; but what occurs within these I can again learn only from perception. And there I soon notice then that in the process which takes place in the eye, there is not a trace of similarity with what I perceive as color. I cannot do away with my perception of color just by showing the process in the eye that takes place in it during this perception. Just as little do I find the color again within the processes of the nerves and brain; I only connect new perceptions within my organism to the first ones which the native person places outside his organism. I only go from one perception to another.
Moreover, there is a break in this whole line of reasoning. I am in a position to follow the occurrences in my organism up to the processes in my brain, even though my conclusions become every more hypothetical the more I approach the central occurrences of the brain. The path of external observation ends with the occurrences in my brain, with that occurrence, in fact, which I would perceive if I could study the brain with the help of physical and chemical means and methods. The path of inner observation begins with the sensation and extends to the construction of things out of the material of sensation. In the transition from brain process to sensation the path of observation is broken.
The way of thinking characterized here, which calls itself “critical idealism” in contradistinction to the standpoint of the naive consciousness which calls itself “naive realism,” makes the mistake of characterizing the one perception as mental picture, while accepting the other in the very same sense as does the native realism which it seemingly had refuted. This way of thinking wants to prove that perceptions have the character of mental pictures, by accepting in naive fashion the perceptions made of one's own organism as objectively valid facts, and in all this still overlooking the fact that it is throwing together two realms of observation, between which it can find no mediation.
Critical idealism can refute naive realism only if it itself accepts, in naive realistic fashion, that one's own organism exits objectively. The moment it becomes conscious of the total similarity in nature between the perceptions made of one's own organism and the perceptions accepted by native realism as existing objectively, it can no longer base itself upon the first kind of perceptions as though they afforded a sure foundation. It would also have to regard one's subjective organization as a mere complex of mental pictures. In so doing, however, it would lose the possibility of thinking that the content of the perceived world is caused by one's spiritual organization. One would have to assume that the mental picture “color” is only a modification of the mental picture “eye.” So-called critical idealism cannot be proven without borrowing from naive realism. The latter is only refuted through the fact that one accepts naive realism's own presuppositions as valid in another area, without examining them there.
From all this, it is certain, at least that critical idealism cannot be proven through investigations within the realm of perception, and that thereby perception cannot be divested of its objective character.
But even less can the thesis, “The perceived world is my mental picture,” be presented as obvious in itself and needing no proof. Schopenhauer begins his principal work, The World as Will and Mental Picture, 6Die Welt als Wille und Vorstellung (usually translated The World as Will and Representation). with the word: “The world is my mental picture: — this is the truth which is valid with respect to every living and knowing being, even though man alone can bring it into reflective abstract consciousness; and if he really does this, then philosophical enlightenment has occurred for him. It will then become definite and certain for him that he knows no sun and no earth, but always only an eye that sees the sun, a hand that feels the earth; that the world which surrounds him is there only as mental picture, i.e., that it absolutely is there only in relationship to something else, to the one doing the mental picturing, which he himself is. — If ever a truth could be declared a priori, it is this one; for it is the expression of that form which every possible and imaginable experience has, that form which is more general than all others, such as time, space and causality; for all these already presuppose the first form ...” This whole thesis founders upon the fact I have already indicated above, that the eye and the hand are no less perceptions than the sun and the earth. And one could, in Schopenhauer's sense and in his own terms, confront his thesis with: My eye that sees the sun, and my hand that feels the earth are my mental pictures in just the same way as the sun and earth themselves are. That I thereby invalidate his thesis, however, is immediately clear. For only my real eye and my real hand could have, connected to them as their own modifications, the mental pictures sun and earth; my mental pictures of eye and hand could not however have these mental pictures. But only of these can critical idealism speak.
Critical idealism is totally unfitted to gain a view of the relationship between perception and mental picture. To distinguish, as indicted on page 49, between what is happening with the perception during the act of perceiving, and what must already be there in the perception before it is perceived — this, critical idealism cannot undertake to do. In order to do this, therefore, another path must be taken.