15. To study physiology with a clear conscience, one must insist on the fact that the sense-organs are not phenomena in the sense of the idealistic philosophy; as such they certainly could not be causes! Sensualism, therefore, at least as regulative hypothesis, if not as heuristic principle. What? And others say even that the external world is the work of our organs? But then our body, as a part of this external world, would be the work of our organs! But then our organs themselves would be the work of our organs! It seems to me that this is a complete REDUCTIO AD ABSURDUM, if the conception CAUSA SUI is something fundamentally absurd. Consequently, the external world is NOT the work of our organs--?
16. There are still harmless self-observers who believe that there are "immediate certainties"; for instance, "I think," or as the superstition of Schopenhauer puts it, "I will"; as though cognition here got hold of its object purely and simply as "the thing in itself," without any falsification taking place either on the part of the subject or the object. I would repeat it, however, a hundred times, that "immediate certainty," as well as "absolute knowledge" and the "thing in itself," involve a CONTRADICTIO IN ADJECTO; we really ought to free ourselves from the misleading significance of words! The people on their part may think that cognition is knowing all about things, but the philosopher must say to himself: "When I analyze the process that is expressed in the sentence, 'I think,' I find a whole series of daring assertions, the argumentative proof of which would be difficult, perhaps impossible: for instance, that it is _I_ who think, that there must necessarily be something that thinks, that thinking is an activity and operation on the part of a being who is thought of as a cause, that there is an 'ego,' and finally, that it is already determined what is to be designated by thinking--that I KNOW what thinking is. For if I had not already decided within myself what it is, by what standard could I determine whether that which is just happening is not perhaps 'willing' or 'feeling'? In short, the assertion 'I think,' assumes that I COMPARE my state at the present moment with other states of myself which I know, in order to determine what it is; on account of this retrospective connection with further 'knowledge,' it has, at any rate, no immediate certainty for me."--In place of the "immediate certainty" in which the people may believe in the special case, the philosopher thus finds a series of metaphysical questions presented to him, veritable conscience questions of the intellect, to wit: "Whence did I get the notion of 'thinking'? Why do I believe in cause and effect? What gives me the right to speak of an 'ego,' and even of an 'ego' as cause, and finally of an 'ego' as cause of thought?" He who ventures to answer these metaphysical questions at once by an appeal to a sort of INTUITIVE perception, like the person who says, "I think, and know that this, at least, is true, actual, and certain"--will encounter a smile and two notes of interrogation in a philosopher nowadays. "Sir," the philosopher will perhaps give him to understand, "it is improbable that you are not mistaken, but why should it be the truth?"
17. With regard to the superstitions of logicians, I shall never tire of emphasizing a small, terse fact, which is unwillingly recognized by these credulous minds--namely, that a thought comes when "it" wishes, and not when "I" wish; so that it is a PERVERSION of the facts of the case to say that the subject "I" is the condition of the predicate "think." ONE thinks; but that this "one" is precisely the famous old "ego," is, to put it mildly, only a supposition, an assertion, and assuredly not an "immediate certainty." After all, one has even gone too far with this "one thinks"--even the "one" contains an INTERPRETATION of the process, and does not belong to the process itself. One infers here according to the usual grammatical formula--"To think is an activity; every activity requires an agency that is active; consequently" . . . It was pretty much on the same lines that the older atomism sought, besides the operating "power," the material particle wherein it resides and out of which it operates--the atom. More rigorous minds, however, learnt at last to get along without this "earth-residuum," and perhaps some day we shall accustom ourselves, even from the logician's point of view, to get along without the little "one" (to which the worthy old "ego" has refined itself). -Friedrich Neitzsche, Jenseits von Gut und Böse