For example take this quote from Nietzsche on the sentence "I think" from Beyond Good and Evil:
>"When I analyze the process that is expressed in this sentence, 'I think,' I find a whole series of daring assertions that would be difficult, perhaps impossible, to prove—for example, 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.
Good luck convincing a skeptic like that to take your definitions for granted, or believe in any conclusions you draw from your definitions.
I would guess that quote is Nietzsche attacking one of the most famous first principles in Western philosophy, Descartes' "I think, therefore I am." "I think" is too complex to be accepted a priori for him, he's not discounting definitions completely.
I think, I would disagree in the sense that he was not only completely discounting on metaphysics, but also on ontology. Because one cannot write up a definition without using the word 'is' he must have been somewhat also completely discounting on definitions. His philosophy is in a sense Heraclitean because it is centered around 'becoming' rather than 'being'.
