THE ESSENCE OF TRUTH
process, then the Platonic statement would have to say that e.g. the self-showing moon, and the psychological process of perceiving the moon, are the same, which is an obvious absurdity. On the other hand, if we hold strictly to what φαντασία means, i.e. the self-showing thing itself, we must ask why αἴσθησις and φαντασία are equated. What must αἴσθησις mean in this case? φαντασία is nothing else but what is perceived as such in its perceivedness, i.e. what shows itself in its self-showing. This leads us to the crucial insight that αἴσθησις means the perceivedness of something. To be sure, perceivedness always involves being perceived and thus the occurrence of a perception. So αἴσθησις has the characteristic double meaning that is also to be found in our word 'perception' , and that plays a special role with Kant: 'the perceived' in its perceivedness, and the 'per-ception' [Wahrnehmen] in which perceivedness occurs.
The thesis is therefore: knowledge, knowing-one's-way-around in something as the possession of truth, i.e. of unhiddenness, is perceivedness. As we have explained it, Theaetetus' statement asserts the identity of αἰσθάνεσθαι and φαντασία, perception and presence. But if we translate this statement along the lines of contemporary psychology it will be declared absurd. Understanding αἴσθησις psychologically as perceptual event misses the essential content of the Greek word. In this case the present problem cannot be comprehended, especially if one also employs a concept of truth and knowledge equally unfaithful to the Greek notion. On the other hand, if we grasp αἴσθησις as the perceivedness of something, it becomes clear that αἴσθησις involves self-showing, facing, presence, i.e. the manifestness of something, a kind of unhiddenness. What αἴσθησις signifies is the immediate unhiddenness of colours, coloured things, sounds and the like. Here, accordingly, is truth; here, accordingly, is knowledge.
It should be noted that Theaetetus does not advance his thesis identifying knowledge and αἴσθησις because perception is presented in the doctrines of psychology as the lowest cognitive faculty and because one should obviously begin at the lowest level. That would be to think in modern terms. Theaetetus also does not refer to αἴσθησις because he is a 'sensualist' and thus a representative of a poor theory of the psychical etc., but because as a Greek he understands αἴσθησις: because perceivedness appears the most immediate mode of the unhiddenness of something, thus the most tangible 'truth'. We can see, therefore, how a clear-thinking mind can come quite spontaneously to this answer, which looks so