»However the question was not, of what there is knowledge, nor how many different kinds of knowledge there are. For we didn't ask with the intention of enumerating them, but to understand knowledge itself, whatever it may be. [...] If somebody asked us about something completely ordinary, such as the nature of clay, and we answered him that there are different kinds of clay, e.g. for potters, for doll-makers or even for brickworks, wouldn't we make ourselves look ridiculous? [...] First of all, by assuming that the questioner could understand the matter from our answer if we simply repeated: clay - even with the addition: clay for the doll-maker, or any other craftsman. Or do you think somebody might understand the notion of something of which he doesn't know what it is? [...]Thus someone who doesn't know what knowledge is will not understand the ›knowledge of shoes‹ [...] It is therefore ridiculous to answer the question: what is knowledge? by mentioning some science [...] That is like describing a never-ending way.«

[Platon: Theaitet, transl. by Schleiermacher, F., Frankfurt am Main: Insel Verlag, 1979, S. 17 ff.]