Plato on Parmenides of Elea: the Eleatic PNC case

According to several scholars, the first explicit formulations of the Principle of Non-Contradiction (PNC) can be found in Plato's works, e. g. in the Republic and the Sophist. The paper defends that, in these two dialogues, the context for that is the discussion of possible consequences of Parmenides' Poem, in which Plato seems to have seen a proto-version of the PNC: it is not possible what is not to be (DK28 B7). In that proto-version, the PNC would present itself as an exhaustive disjunction: either it is, and cannot not be, or it is not, and cannot be; and tertium non datur (DK28 B2, B8, passim). The paper shows the problematic corollaries thereof pointed to by Plato in the Republic and the Sophist, as well as it analyses the solutions that he had presented in each dialogue for those problems, namely, his own versions of the PNC.