An interpretation of the “Parmenides” is proposed in base to the Plato’s “unwritten doctrines”. The greek author demonstrates in this dialogue that with the One only is impossible to think (hypothesis I), and this is why a principle of difference is required; that with the ontological conception of this difference neither, because contradictory conclusions would be followed (hypothesis II); and that without the One isimpossible to think, too (hypothesis III). These conclusions suggest the reader that the One is necessary to (...) think, but another or other principles must be searched to stablish a dialectic. Plato confirms this way the parenetic character of his dialogues respecting at the same time the selfconstrained taboo of the “unwritten doctrines” (he doesn’t mention the undefinite dyad). To come to these conclusions the author ofthis paper proposes a plan of the second part of this work, that divides it in three hypothesis, not in eight, like is usual today, and analyzes the categories that sustain the argumentatives subdivisions of each one of the hypotheses: the structure of all the hypotheses is the same. All this in critical discussion with the actual bibliography about the topics. (shrink)