Sophist

The dialogue's spine is the argument that defining the sophist as a producer of false images requires abandoning Parmenides' prohibition on not-being. The Eleatic Stranger pursues the sophist through the method of division, arriving at a figure who traffics in appearances and deception . But this definition generates a crisis: if the sophist says what is false, then not-being must somehow exist—a conclusion Parmenides forbade. The dialogue rejects the Eleatic assumption that not-being is simply the opposite of being. Instead, Plato argues that 'not-being' means 'different from,' a positive relation among things that are . This is the 'parricide' of Parmenides, and it is the dialogue's central philosophical achievement.

The Sophist introduces the method of division (diairesis) as a technique for definition, illustrated through the extended hunt for the sophist via bifurcations of kinds . More significantly, it introduces the theory of the five greatest kinds—Being, Motion, Rest, Sameness, and Difference—and the concept of the 'communion of kinds' (symploke eidon), which explains how different Forms can be predicated of one another . This framework is the foundation for Plato's solution to falsehood: a statement is false when it says 'different' rather than 'same' about its subject. The method of division influenced later taxonomic thinking, and the analysis of predication and difference remains central to contemporary readings of Plato's philosophy of language .

The 'parricide' is the Eleatic Stranger's admission that, to save the possibility of falsehood, he must contradict Parmenides' claim that not-being cannot be thought or spoken. Parmenides had argued that whatever is spoken of must be something, so false statements are impossible. The Stranger shows that this position makes the sophist invulnerable: if falsehood is impossible, the sophist cannot be a deceiver. The solution is to reinterpret not-being not as the absolute opposite of being but as Difference—the fact that any given thing is not any number of other things . With this move, the Stranger can say that a false statement 'says what is not' in the sense that it conjoins terms that are different from one another, without invoking absolute nothingness .

The choice of the Eleatic Stranger as the lead speaker is philosophically significant. Socrates is present but silent, a departure from most Platonic dialogues . The Stranger comes from Elea, Parmenides' home, and he brings a different method—division rather than Socratic elenchus—to the inquiry. This allows Plato to stage a confrontation with Eleatic philosophy from within, as it were: the Stranger is the one who must commit the parricide against his own tradition. Some scholars argue that Plato avoids putting the dialogue's most dogmatic conclusions in Socrates' mouth, preserving a distance between the historical Socrates and the metaphysical positions developed here . The silence of Socrates thus marks a transition in Plato's late philosophy.

The Sophist is set on the day after the Theaetetus and continues its inquiry . The Theaetetus ended in aporia, having failed to define knowledge. The Sophist does not return to the question of knowledge directly but addresses a problem that the Theaetetus raised: the possibility of false belief. In the Theaetetus, false belief seemed impossible because one cannot believe what is not. The Sophist solves this by reinterpreting not-being as difference, making falsehood intelligible . In this sense, the later dialogue resolves a puzzle left open by the earlier one, though it does so by shifting from epistemology to ontology. The two dialogues are often read as a pair, moving from the failure to define knowledge to the metaphysical conditions that make error possible.