[48] Diog. Laërt. VII 41. τὸ δὲ λογικὸν μέρος φασὶν ἔνιοι εἰς δύο διαιρεῖσθαι ἐπιστήμας, εἰς ῥητορικὴν καὶ εἰς διαλεκτικήν. — — 42. τήν τε ῥητορικὴν ἐπιστήμην οὖσαν τοῦ εὖ λέγειν περὶ τῶν ἐν διεξόδῳ λόγων καὶ τὴν διαλεκτικὴν τοῦ ὀρθῶς διαλέγεσθαι περὶ τῶν ἐν ἐρωτήσει καὶ ἀποκρίσει λόγων· ὅθεν καὶ οὕτως αὐτὴν ὁρίζονται· ἐπιστήμην ἀληθῶν καὶ ψευδῶν καὶ οὐδετέρων.