The sophist who reached the highest spiritual level and who was esteemed accordingly even by Plato and Aristotle was Protagoras of Abdera. His work did not in fact stop with rhetoric, but in connection with reflections on speech he contributed to the development of certain basic grammatical concepts. Likewise Prodikos of Keos engaged in the question of significative nexuses.2
Aristotle's judgment on sophistry is basically the same as Plato's. The determination we encountered in Aristotle, namely that σοφιστική is φιλοσοφία φαινομένη, οὖσα δ' οὔ (cf. Met. IV, 2, 1004b26), we find almost verbatim in Plato's Sophist: πάντα ἄρα σοφοὶ τοῖς μαθηταῖς φαίνονται (233c8), "they seem to be and they pretend to be disciples in every respect, ones who know and understand." σοφοὶ φαίνονται, hence φιλοσοφία φαινομένη, οὖσα δ' οὔ. Plato says οὐκ ὄντες γε (233c8), "in fact they are not." The sophists do not have ἀλήθεια, i.e., their speaking does not disclose the things, but, instead, the sophists move in a δοξαστικὴ περὶ πάντων ἐπιστήμην (cf. 233c10), in a knowing which is only δοξαστικὴ, which only looks like knowing and which claims to extend to everything. It only looks that way, it is only presumed knowledge, because it moves only in determinate opinions. Δοξαστικὴ is to be taken in a double sense: on the one hand, it means the same as φαινομένη, "apparently," and at the same time there resides in it the reason this ἐπιστήμη is φαινομένη: because it does not provide ἀλήθεια but only δόξαι, opinions on matters, not the matters at issue themselves.
d) Ἀληθεύειν as ground of the question of μὴ ὄν (= ψεῦδος).
Our reflection on ἀληθεύειν has at the same time also provided the ground needed to understand why the sophist becomes thematic in the question about the Being of non-beings. That is, insofar as ἀληθεύειν has the sense of the uncovering of beings in their Being,3 then its opposite, ψεύδεσθαι, distorting, deceiving, is the mode of comportment in which beings are covered over and distorted, the mode in which something shows itself—or "is"—as something it basically is not. The result is that non-being can be exhibited as being through the factual existence of error and deception. This is the inner connection between ἀληθές and ὄν, and between ψεῦδος and μὴ ὄν. The task is to draw closer to ψεύδεσθαι in order to gain the ground for presentifying μὴ ὄν itself.
2. See the appendix.
3. AH: ἀλήθεια—beingness.