This dissertation examines a passage from Plato s Sophist. Our objective is to offer an account of the platonic reading of the Parmenides Poem presupposed by the aporíai of not-being in the passage that goes from 236e to 441a. This passage begins with a direct quotation of two verses from fragment B7 of Parmenides s Poem and ends with the famous passage of the parricid. Between these two passages, are expounded and related to the Parmenides Poem five sophistic arguments. This passage, therefore, is very important for the understanding of the influence of Parmenides of Elea in the development of platonic metaphysics. Traditionally, this passage is interpreted as an acceptance of the connection between the parmenidean theses and the sophistic arguments against the notion of image and false speech, in a way that the parricide is seen as a direct refutation of Parmenides. However, the proponents of this traditional interpretation start from an erroneous methodological principle, that consists of adopting an external and independent interpretation of Parmenides and then try to determine the use that Plato makes of Parmenides in this dialogue in reference to this independent interpretation. This being thus, we will try to show, by means of a direct translation from the original greek text and the reading of recent studies on the subject, that Plato is engaged in a double mission: (i) to save the legacy of Parmenides from certain sophistic appropriations and (ii) to reiterate and to strengthen his own interpretation of Parmenides, on which important metaphysical decisions of the Theory of Forms of the middle period dialogues are supported.