In this paper the Author examines the problem of not-being in Plato’s Sophist. "Notbeing" is closely connected in Plato’s Sophist with the notion of the "other" or "difference" since not-being can be understood as "not-being something", that is, as "different from" something. In fact, what "is not" beautiful, for example, is not only what is "contrary" to beautiful but also what is "different" from beautiful. Thus, the "other" introduces and explains the notion of a relative "not-being" as "different" from what it is. The Author puts this idea at the center of the analysis in an attempt to verify its coherence and legitimacy and establish some connections with two contemporary thinkers, Meinong and Frege, who clearly depend on Plato’s reflections on this point.
Keywords: Plato, Parmenides, sophist, not-being, difference, dialectic