The whole observation given above in Euler’s words, and which is quite correct, affords a fresh proof of Kant’s Transcendental Æsthetic, and of my theory of perception which is founded upon it, as also of idealism in general. The directness and unconsciousness referred to above, with which in perception we make _the transition from the sensation to its cause_, may be illustrated by an analogous procedure in the use of abstract ideas or thinking. When we read or hear we receive mere words, but we pass from these so immediately to the conceptions denoted by them, that it is as if we _received the conceptions directly_; for we are absolutely unconscious of the transition from the words to the conceptions. Therefore it sometimes happens that we do not know in what language it was that we read something yesterday which we now remember. Yet that such a transition always takes place becomes apparent if it is once omitted, that is, if in a fit of abstraction we read without thinking, and then become aware that we certainly have taken in all the words but no conceptions. Only when we pass from abstract conceptions to pictures of the imagination do we become conscious of the transposition we have made. Further, it is really only in perception in the narrowest sense, that is, in _sight_, that in empirical apprehension the transition from the sensation to its cause takes place quite unconsciously. In every other kind of sense perception, on the contrary, the transition takes place with more or less distinct consciousness; therefore, in the case of apprehension through the four coarser senses, its reality is capable of being established as an immediate fact. Thus in the dark we feel a thing for a long time on all sides until from the different effects upon our hands we are able to construct its definite form as their cause. Further, if something feels smooth we sometimes reflect whether we may not have fat or oil upon our hands; and again, if something feels cold we ask ourselves whether it may not be that we have very warm hands. When we hear a sound we sometimes doubt whether it was really an affection of our sense of hearing from without or merely an inner affection of it; then whether it sounded near and weak or far off and strong, then from what direction it came, and finally whether it was the voice of a man or of a brute, or the sound of an instrument; thus we investigate the cause of each effect we experience. In the case of smell and taste uncertainty as to the objective nature of the cause of the effect felt is of the commonest occurrence, so distinctly are the two separated here. The fact that _in sight_ the transition from the effect to the cause occurs quite unconsciously, and hence the illusion arises that this kind of perception is perfectly direct, and consists simply in the sensation alone without any operation of the understanding—this has its explanation partly in the great perfection of the organ of vision, and partly in the exclusively