A reader of whose powers the author of this book has a very high opinion, has objected that it is impossible to speak about thinking as we are here doing, because the supposed observation of active thinking is nothing but an illusion. In reality, what is observed is only the results of an unconscious activity which lies at the basis of thinking. It is only because, and just because, this unconscious activity escapes observation, that the deceptive appearance of the self-existence of the observed thinking arises, just as when an illumination by means of a rapid succession of electric sparks makes us believe that we see a movement. This objection, likewise, rests solely on an inaccurate view of the facts. The objection ignores that it is the Ego itself which, identical with the thinking, observes from within its own activity. The Ego would have to stand outside the thinking in order to suffer the sort of deception which is caused by an illumination with a rapid succession of electric sparks. One might say rather that to indulge in such an analogy is to deceive oneself wilfully, just as if someone, seeing a moving light, were obstinately to affirm that it is being freshly lit by an unknown hand at every point where it appears. No, whoever is bent on seeing in thought anything else than an activity produced--and observable by--the Ego has first to shut his eyes to the plain facts that are there for the looking, in order then to invent a hypothetical activity as the basis of thinking. If he does not wilfully blind himself, he must recognise that all these "hypothetical additions" to thinking take him away from its real nature. Unprejudiced observation shows that nothing is to be counted as belonging to the nature of thinking except what is found in thinking itself. It is impossible to discover the cause of thinking by going outside the realm of thought. IV THE WORLD AS PERCEPT