hen 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

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 ma

that, as man grows up, he slowly and gradually builds up the concepts corre

ghout 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

s data from perception alone, one must demand also that it abandon all thou

een 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 its

ng 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. Ra

aces himself and the rest of the world. But by this same act of thought he d

o far simply called the perceptual object and which comes, in con

s everything which has been imported by thought. For, at any moment, the content o

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 n

nsidered as merely subjective, then we shall not be tempted to believe tha

ht what relation the above-mentioned immediate

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

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 manne

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

ed to make these continual co

ture 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

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 fur

nd 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

e 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

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 kn

f 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 Sel

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

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

at 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 sensati

he 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 o

ht 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 ful

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 obse

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?ve

ctive 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 w

percepts cannot establish Critical Idealism, and, conseq

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

separation, mentioned on p. 58, between what happens to the percept in the process of perception and what must