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of all philosophy and all reflection in general, although in modern days

it has taken its place as a great new discovery even among naturalists

themselves, by whom it is extolled and recognised as "the conquest of

materialism." Such exaggerated emphasis tends to conceal the fact that

this truth has been regarded as self-evident from very early times.



What is a body, extension, movement, colour, smell and taste? What do I

possess of them, or know of them, except through the images, sensations

and feelings which they call up in my receptive mind? No single thing

wanders into me as itself, or reveals itself to me directly; only through

the way in which they affect me, the peculiar changes which they work in

me, do things reveal to me their existence and their special character. I

have no knowledge of an apple-tree or of an apple, except through the

sense perceptions they call up in me. But these sense perceptions, what

are they but different peculiar states of my consciousness, peculiar

determinations of my mind? I see that the tree stands there, but what is

it to see? What is the perception of a colour, of light, of shade, and

their changes? Surely only a peculiar change of my mind itself, a

particular state of stimulus and awareness brought about in myself. And in

the same way I can feel that the apple lies there. But what is the

perception of resistance, of hardness, of impenetrability? Nothing more

than a feeling, a change in my psychical state, which is unique and cannot

be described in terms of anything but itself. Even as regards "attraction

and repulsion," external existence only reveals itself to us through

changes in the mind and consciousness, which we then attribute to a cause

outside ourselves.



It is well enough known that this simple but incontrovertible fact has

often led to the denial of the existence of anything outside of ourselves

and our consciousness. But even if we leave this difficult subject alone,

it is quite certain that, if the question as to the pre-eminence of

consciousness and its relation to external things is to be asked at all,

it should be formulated as follows, and not conversely: "How can I,

starting from the directly given reality and certainty of consciousness

and its states, arrive at the certainty and reality of external things,

substances, forces, physics and chemistry?"