The products of thinking are concepts and ideas. 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 perceives a tree, the perception acts as a stimulus for thought. Thus an ideal element is added to the perceived object, and the perceiver regards the object and its ideal complement as belonging together. When the object disappears from the field of his perception, the ideal counterpart alone remains. This latter is the concept of the object. The wider the range of our experience, the larger becomes the number of our concepts. Moreover, concepts are not by any means found in isolation one from the other. They combine to form an ordered and systematic whole. The concept “organism,” e.g., combines with those of “development according to law,” “growth,” and others. Other concepts based on particular objects fuse completely with one another. All concepts formed from particular lions fuse in the universal concept “lion.” In this way, [49]all the separate concepts combine to form a closed, conceptual system within which each has its special place. Ideas do not differ qualitatively from concepts. They are but fuller, more saturated, more comprehensive concepts. I attach special importance to the necessity of bearing in mind, here, that I make thought my starting-point, and not concepts and ideas which are first gained by means of thought. These latter presuppose thought. My remarks regarding the self-dependent, self-sufficient character of thought 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 ultimate.)

Concepts cannot be derived from perception. This is apparent from the fact that, as man grows up, he slowly and gradually builds up the concepts corresponding to the objects which surround him. Concepts are added to perception.

A philosopher, widely read at the present day (Herbert Spencer), describes the mental process which we perform upon perception 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 [50]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 generalised 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” (First Principles, Part I, par. 23). A closer analysis leads to a very different description from that here given. When I hear a noise, my first demand is for the concept which fits this percept. Without this concept, the noise is to me a mere noise. Whoever does not reflect further, hears just the noise and is satisfied with that. But my thought makes it clear to me that the noise is to be regarded as an effect. Thus it is only when I combine the concept of effect with the percept of a noise that I am led to go beyond the particular percept and seek for its cause. The concept of “effect” calls up that of “cause,” and my next step is to look for the agent, which I find, say, in a partridge. But these concepts, cause and effect, can never be gained through mere perception, however many instances we bring under review. Perception evokes thought, and it is this which shows me how to link separate experiences together.

If one demands of a “strictly objective [51]science” that it should take its data from perception alone, one must demand also that it abandon all thought. For thought, by its very nature, transcends the objects of perception.

It is time now to pass from thought to the thinker. For it is through the thinker that thought and perception are combined. The human mind is the stage on which concept and percept meet and are linked to one another. In saying this, we already characterise this (human) consciousness. It mediates between thought and perception. In perception the object appears as given, in thought the mind seems to itself to be active. It regards the thing as object and itself as the thinking subject. When thought is directed upon the perceptual world we have consciousness of objects; when it is directed upon itself we have self-consciousness. Human consciousness must, of necessity, be at the same time self-consciousness, because it is a consciousness which thinks. For, when thought contemplates its own activity it makes an object for study of its own essential nature, it makes an object of itself as subject.

It is important to note here that it is only by means of thinking that I am able to determine myself as subject and contrast myself with objects. Therefore thinking must never be regarded as a merely subjective activity. Thinking transcends the distinction of subject and object. It produces these two concepts [52]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, but thought, which makes the reference. The subject does not think because it is a subject, rather it conceives itself to be a subject because it can think. The activity of consciousness, in so far as it thinks, is thus not merely subjective. Rather it is neither subjective nor objective; it transcends both these concepts. I ought never to say that I, as an individual subject, think, but rather that I, as subject, exist myself by the grace of thought. Thought thus takes me out of myself and relates me to objects. At the same time it separates me from them, inasmuch as I, as subject, am set over against the objects.

It is just this which constitutes the double nature of man. His thought embraces himself and the rest of the world. But by this same act of thought he determines himself also as an individual, in contrast with the objective world.

We must next ask ourselves how the other element, which we have so far simply called the perceptual object and which comes, in consciousness, into contact with thought, enters into thought at all?

In order to answer this question, we must eliminate from the field of consciousness everything which has been imported by thought. For, at any moment, the content of consciousness [53]is always shot through with concepts in the most various ways.

Let us assume that a being with fully developed human intelligence originated out of nothing and confronted the world. All that it there perceived before its thought began to act would be the pure content of perception. The world so far would appear to this being as a mere chaotic aggregate of sense-data, colours, sounds, sensations of pressure, of warmth, of taste, of smell, and, lastly, feelings of pleasure and pain. This mass constitutes the world of pure unthinking perception. Over against it stands thought, ready to begin its activity as soon as it can find a point of attack. Experience shows that the opportunity is not long in coming. Thought is able to draw threads from one sense-datum to another. It brings definite concepts to bear on these data and thus establishes a relation between them. We have seen above how a noise which we hear is connected with another content by our identifying the first as the effect of the second.

If now we recollect that the activity of thought is on no account to be considered as merely subjective, then we shall not be tempted to believe that the relations thus established by thought have merely subjective validity.

Our next task is to discover by means of thought what relation the above-mentioned immediate sense-data have to the conscious subject. [54]

The ambiguity of current speech makes it advisable for me to come to an agreement with my readers concerning the meaning of a word which I shall have to employ in what follows. I shall apply the name “percepts” to the immediate sense-data enumerated above, in so far as the subject consciously apprehends them. It is, then, not the process of perception, but the object of this process which I call the “percept.”

I reject the term “sensation,” because this has a definite meaning in Physiology which is narrower than that of my term “percept.” I can speak of feeling as a percept, but not as a sensation in the physiological sense of the term. Before I can have cognisance of my feeling it must become a percept for me. The manner in which, through observation, we gain knowledge of our thought-processes is such that when we first begin to notice thought, it too may be called a percept.

The unreflective man regards his percepts, such as they appear to his immediate apprehension, as things having a wholly independent existence. When he sees a tree he believes that it stands in the form which he sees, with the colours of all its parts, etc., 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 the phenomenon exists and occurs (by itself) exactly as he perceives it. To this belief he clings until [55]he meets with further percepts which contradict his former ones. The child who has as yet had no experience of distance grasps at the moon, and does not correct its first impression as to the real distance until 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 mental 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 contradicted percepts which in those early days were unknown. A man who had been born blind said, when operated on by Dr. Franz, that the idea of the size of objects which he had formed before his operation by his sense of touch 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 in our observations?

A single reflection supplies 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. But the scene which I perceive changes when I change the place from which I am looking. The exact form in which it presents itself to me is, therefore, dependent on a condition which inheres, not in the object, but in me, the percipient. It is [56]all the same to the avenue where I stand. But the picture of it which I receive depends essentially on my standpoint. In the same way, it makes no difference to the sun and the planetary system that human beings happen to perceive them from the earth; but the picture of the heavens which human beings have is determined by the fact that they inhabit the earth. This dependence of our percepts on our points of observation is the easiest kind of dependence to understand. The matter becomes more difficult when we realise further that our perceptual world is dependent on our bodily and mental organisation. The physicist teaches us that within the space in which we hear a sound there are vibrations of the air, and that there are vibrations also in the particles of the body which we regard as the cause of the sound. These vibrations are perceived as sounds only if we have normally constructed ears. Without them the whole world would be for us for ever silent. Again, the physiologist teaches us that there are men who perceive nothing of the wonderful display of colours which surrounds us. In their world there are only degrees of light and dark. Others are blind only to one colour, e.g., red. Their world lacks this colour tone, and hence it is actually a different one from that of the average man. I should like to call the dependence of my perceptual world on my point of observation “mathematical,” and its dependence on my organisation “qualitative.” The [57]former determines 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 structure of my eye.

My percepts, 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 know that a percept, e.g., that of a red colour 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 being at all apart from our subjective organisation, that it has no kind of existence apart from the act of perceiving of which it is the object. The classical representative of this theory is George Berkeley, who held that from the moment we realise the importance of a subject for perception, we are no longer able to believe in the existence of a world apart from a conscious mind. “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, viz., that all the choir of heaven and the 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 [58]spirit, they must either have no existence at all or else subsist in the mind of some Eternal Spirit” (Berkeley, Of the Principles of Human Knowledge, Part I, Section 6).

On this view, when we take away the act of perceiving, nothing remains of the percept. There is no colour when none is seen, no sound when none is heard. Extension, form, and motion exist as little as colour and sound apart from the act of perception. We never perceive bare extension or shape. These are always joined with colour or some other quality, which are undoubtedly dependent on the subject. If these latter disappear when we cease to perceive, the former, being connected with them, must disappear likewise.

If it is urged that, even though figure, colour, sound, etc., have no existence except in the act of perception, yet there must be things which exist apart from perception and which are similar to the percepts in our minds, then the view we have mentioned would answer, that a colour can be similar only to a colour, a figure to a figure. Our percepts can be similar only to our percepts and to nothing else. Even what we call a thing is nothing but a collection of percepts which are connected in a definite way. If I strip a table of its shape, extension, colour, etc.—in short, of all that is merely my percepts—then nothing remains over. If we follow this view to its logical conclusion, we are led to the assertion that the objects of my perceptions [59]exist only through me, and 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 we take into account merely the general fact that the percept is determined in part by the organisation of the subject. The matter would be far otherwise if we were in a position to say what part exactly is played by our perceiving in the occurrence of a percept. We should know then what happens to a percept whilst it is being perceived, and we should also be able to determine what character it must possess before it comes to be perceived.

This leads us to turn our attention from the object of a perception to the subject of it. I am aware not only of other things but also of myself. The content of my perception of myself consists, in the first instance, in that I am something stable in contrast with the ever coming and going flux of percepts. The awareness of myself accompanies in my consciousness the awareness of all other percepts. When I am absorbed in the perception of a given object I am, for the time being, aware only of this object. Next I become aware also of myself. I am then conscious, not only of the object, but also of my Self as opposed to and observing the object. I do not merely [60]see a tree, I know also that it is I who see it. I know, moreover, that some process takes place in me when I observe a tree. When the tree disappears from my field of vision, an after-effect of this process remains, viz., an image of the tree. This image has become associated with my Self during my perception. My Self has become enriched; to its content a new element has been added. This element I call my idea of the tree. I should never have occasion to talk of ideas, were I not aware of my own Self. Percepts would come and go; I should let them slip by. It is only because I am aware of my Self, and observe that with each perception the content of the Self is changed, that I am compelled to connect the perception of the object with the changes in the content of my Self, and to speak of having an idea.

That I have ideas is in the same sense matter of observation to me as that other objects have colour, sound, etc. I am now also able to distinguish these other objects, which stand over against me, by the name of the outer world, whereas the contents of my perception of my Self form my inner world. The failure to recognise the true relation between idea and object has led to the greatest misunderstandings in modern philosophy. The fact that I perceive a change in myself, that my Self undergoes a modification, has been thrust into the foreground, whilst the object which causes these modifications is altogether ignored. [61]In consequence it has been said that we perceive, not objects, but only our ideas. I know, so it is said, nothing of the table in itself, which is the object of my perception, but only of the changes which occur within me when I perceive a table. This theory should not be confused with the Berkeleyan theory mentioned above. Berkeley maintains the subjective nature of my perceptual contents, but he does not say that I can know only my own ideas. He limits my knowledge to my ideas because, on his view, there are no objects other than ideas. What I perceive as a table no longer exists, according to Berkeley, when I cease to look at it. This is why Berkeley holds that our percepts are created directly by the omnipotence of God. I see a table because God causes this percept in me. For Berkeley, therefore, nothing is real except God and human spirits. What we call the “world” exists only in spirits. What the na?ve man calls the outer world, or material 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 ideas, not because of any conviction that nothing beyond these ideas exists, but because it holds that we are so organised that we can have knowledge only of the changes within our own selves, not of the things-in-themselves which are the causes of these changes. This view concludes from the fact that I know only my own ideas, not that [62]there is no reality independent of them, but only that the subject cannot have direct knowledge of such reality. The mind can merely “through the medium of its subjective thoughts imagine it, conceive it, know it, or perhaps also fail to know it” (O. Liebmann, Zur Analysis der Wirklichkeit, p. 28). Kantians believe that their principles are absolutely certain, indeed immediately evident, without any proof. “The most fundamental principle which the philosopher must begin by grasping clearly, consists in the recognition that our knowledge, in the first instance, does not extend beyond our ideas. Our ideas are all that we immediately have and experience, and just because we have immediate experience of them the most radical doubt cannot rob us of this knowledge. On the other hand, the knowledge which transcends my ideas—taking ideas 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 philosophy we must explicitly set down all knowledge which transcends ideas as open to doubt.” These are the opening sentences of Volkelt’s book on Kant’s Theory of Knowledge. What is here put forward as an immediate and self-evident truth is, in reality, the conclusion of a piece of argument which runs as follows. Na?ve common sense believes that things, just as we perceive them, exist also outside our minds. Physics, Physiology, and Psychology, however, teach us that our percepts [63]are dependent on our organisation, and that therefore we cannot know anything about external objects except what our organisation transmits to us. The objects which we perceive are thus modifications of our organisation, not things-in-themselves. This line of thought has, in fact, been characterised by Ed. von Hartmann as the one which leads necessarily to the conviction that we can have direct knowledge only of our own ideas (cp. his Grundproblem der Erkenntnistheorie, pp. 16–40). Because outside our organisms we find vibrations of particles and of air, which are perceived by us as sounds, it is concluded that what we call sound is nothing more than a subjective reaction of our organisms to these motions in the external world. Similarly, colour and heat are inferred to be merely modifications of our organisms. And, further, these two kinds of percepts are held to be the effects of processes in the external world which are utterly different from what we experience as heat or as colour. When these processes stimulate the nerves in the skin of my body, I perceive heat; when they stimulate the optical nerve I perceive light and colour. Light, colour, and heat, then, are the reactions of my sensory nerves to external stimuli. Similarly, the sense of touch reveals to me, not the objects of the outer world, but only states of my own body. The physicist holds that bodies are composed of infinitely small particles called molecules, and that these [64]molecules are not in direct contact with one another, but have definite intervals between them. Between them, therefore, is empty space. Across this space they act on one another by 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 experience only its effects on my organism.

The theory of the so-called Specific Nervous Energy, which has been advanced by J. Müller, supplements these speculations. It asserts that each sense has the peculiarity that it reacts to all external stimuli in only one definite way. If the optic nerve is stimulated, light sensations result, irrespective of whether the stimulation is due to what we call light, or to mechanical pressure, or an electrical current. On the other hand, the same external stimulus applied to different senses gives rise to different sensations. The conclusion from these facts seems to be, that our sense-organs can give us knowledge only of what occurs in themselves, but not of the external world. They determine our percepts, each according to its own nature.

Physiology shows, further, that there can be no direct knowledge even of the effects [65]which objects produce on our sense-organs. Through his study of the processes which occur in our own bodies, the physiologist finds that, even in the sense-organs, the effects of the external process are modified in the most diverse 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 modified stimulus is then conducted to the brain. Here the central organs must in turn be stimulated. The conclusion is, therefore, drawn that the external process undergoes a series of transformations before it reaches consciousness. The brain processes are connected by so many intermediate links with the external stimuli, that any similarity between them 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 apprehended immediately 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 with the process which occurs in the brain when I sense red. The sensation, again, occurs as an effect in the mind, and the brain process is only its cause. This is why Hartmann (Grundproblem der Erkenntnistheorie, p. 37) says, “What the subject experiences is therefore only modifications [66]of his own psychical states and nothing else.” However, when I have sensations, they are very far as yet from being grouped in those complexes which 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 organ of touch, those of colour and light by the organ of sight. Yet all these are found united in one object. This unification must, therefore, be brought about by the soul itself; that is, the soul constructs things out of the separate sensations which the brain conveys to it. My brain conveys to me singly, and by widely different paths, the visual, tactual, and auditory sensations which the soul then combines into the idea of a trumpet. Thus, what is really the result of a process (i.e., the idea of a trumpet), is for my consciousness the primary datum. In this result nothing can any longer be found of what exists outside of me and originally stimulated my sense-organs. The external object is lost entirely on the way to the brain and through the brain to the soul.

It would be hard to find in the history of human speculation 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. The theory starts with what is given in na?ve consciousness, i.e., with things as perceived. It proceeds to show that none of the qualities which we find in [67]these things would exist for us, had we no sense-organs. No eye—no colour. Therefore, the colour is not, as yet, present in the stimulus which affects the eye. It arises first through the interaction of the eye and the object. The latter is, therefore, colourless. But neither is the colour 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 colour. That is only produced in the soul by means of the brain process. Even then it does not yet appear in consciousness, but is first referred by the soul to a body in the external world. There I finally perceive it, as a quality of this body. We have travelled in a complete circle. We are conscious of a coloured object. That is the starting-point. Here thought begins its construction. If I had no eye, the object would be, for me, colourless. I cannot, therefore, attribute the colour to the object. I must look for it elsewhere. I look for it, first, 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 object. I recover the coloured body only on returning to my starting-point. The circle is completed. The theory leads me to identify what the na?ve man regards as existing outside of him, as really a product of my mind.

As long as one stops here everything seems [68]to fit beautifully. But we must go over the argument once more from the beginning. Hitherto I have used, as my starting-point, the object, i.e., the external percept of which up to now, from my na?ve standpoint, I had a totally wrong conception. I thought that the percept, just as I perceive it, had objective existence. But now I observe that it disappears with my act of perception, that it is only a modification of my mental state. 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 an idea of itself in me, as itself an idea. But from this it follows logically that my sense-organs, and the processes in them are also merely subjective. I have no right to talk of a real eye but only of my idea of an eye. Exactly the same is true of the nerve paths, and the brain processes, and even of the process in the soul itself, through which things are supposed to be constructed out of the chaos of diverse sensations. If assuming the truth of the first circle of argumentation, I run through the steps of my cognitive activity once more, the latter reveals itself as a tissue of ideas which, as such, cannot act on one another. I cannot say that my idea of the object acts on my idea of the eye, and that from this interaction results my idea of colour. But it is necessary that I should say this. For as soon as I see clearly that my sense-organs and [69]their activity, my nerve- and soul-processes, can also be known to me only through perception, the argument 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 touches it, but what takes place in these I can, in turn, learn only from perception. And then I soon perceive that there is no trace of similarity between the process which takes place in the eye and the colour which I see. I cannot get rid of colour sensations by pointing to the process which takes place in the eye whilst I perceive a colour. No more can I re-discover the colour in the nerve- or brain-processes. I only add a new percept, localised within the organism, to the first percept which the na?ve man localises outside of his organism. I only pass from one percept to another.

Moreover, there is a break 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 method of external observation ceases with the process in my brain, more particularly with the process which I should observe, if I could treat the brain with the instruments and methods of Physics and [70]Chemistry. The method of internal observation, or introspection, begins with the sensations, and includes the construction of things out of the material of sense-data. At the point of transition from brain process to sensation, there is a break in the sequence of observation.

The theory which I have here described, and which calls itself Critical Idealism, in contrast to the standpoint of na?ve common sense which it calls Na?ve Realism, makes the mistake of characterising one group of percepts as ideas, whilst taking another group in the very same sense as the Na?ve Realism which it apparently refutes. It establishes the ideal character of percepts by accepting na?vely, as objectively valid facts, the percepts connected with one’s own body; and, in addition, it fails to see that it confuses two spheres of observation, between which it can find no connecting link.

Critical Idealism can refute Na?ve Realism only by itself assuming, in na?ve-realistic fashion, that one’s own organism has objective existence. As soon as the Idealist realises that the percepts connected with his own organism stand on exactly the same footing as those which Na?ve Realism assumes to have objective existence, he can no longer use the former as a safe foundation for his theory. He would, to be consistent, have to regard his own organism also as a mere complex of ideas. But this removes the possibility of regarding the [71]content of the perceptual world as a product of the mind’s organisation. One would have to assume that the idea “colour” was only a modification of the idea “eye.” So-called Critical Idealism can be established only by borrowing the assumptions of Na?ve Realism. The apparent refutation of the latter is achieved only by uncritically accepting its own assumptions as valid in another sphere.

This much, then, is certain: Analysis within the world of percepts cannot establish Critical Idealism, and, consequently, cannot strip percepts of their objective character.

Still less is it legitimate to represent the principle that “the perceptual world is my idea” as self-evident and needing no proof. Schopenhauer begins his chief work, The World as Will and Idea, with the words: “The world is my idea—this is a truth which holds good for everything that lives and knows, though man alone can bring it into reflective and abstract consciousness. If he really does this, he has attained to philosophical wisdom. It then becomes clear and certain to him that what he knows is not a sun and an earth, but only an eye that sees a sun, a hand that feels an earth; that the world which surrounds him is there only in idea, i.e., only in relation to something else, the consciousness which is himself. If any truth can be asserted a priori, it is this: for it is the expression of the most general form of all possible and thinkable [72]experience, a form which is more general than time, or space, or causality, for they all presuppose it …” (The World as Will and Idea, Book I, par. 1). This whole theory is wrecked by the fact, already mentioned above, that the eyes and the hand are just as much percepts as the sun and the earth. Using Schopenhauer’s vocabulary in his own sense, I might maintain against him that my eye which sees the sun, and my hand which feels the earth, are my ideas just like the sun and the earth themselves. That, put in this way, the whole theory cancels itself, is clear without further argument. For only my real eye and my real hand, but not my ideas “eye” and “hand,” could own the ideas “sun” and “earth” as modifications. Yet it is only in terms of these ideas that Critical Idealism has the right to speak.

Critical Idealism is totally unable to gain an insight unto the relation of percept to idea. It cannot make the separation, mentioned on p. 58, between what happens to the percept in the process of perception and what must be inherent in it prior to perception. We must therefore attempt this problem in another way.