Protagoras (Πρωταγόρας), the first of that class of Greek philosophers who took the name of Sophists (q.v.), flourished near the opening of the 5th century B.C. He was a native of Abdera, according to the concurrent testimony of Plato and several other writers (Proftag. p. 309, c; De Rtep. 10:p. 606, c; Heraclides Pont. ap. Diog. Laert. 9:55; Cicero, De Nat. Deor. i, 23, etc.). There seems to be no ground for the story that he was in early life employed in manual labor, nor for the supposition that he was a disciple of Democritus, with whom in point of doctrine he had absolutely nothing in common. Protagoras must have been older than Democritus, as it is certain that Protagoras was older than Socrates, who was born B.C. 468 (Plato, Protag. p. 317, c; 314, b; 361, e; comp. Diog. Laert. 9:42, 56), and died before him at the age of nearly seventy (Plato, Meno, p. 91, e; comp. Thecet. p. 171, d; 164, e; Euthyd. p. 286, c), after he had practiced the sophistic art for forty years in various Greek cities, especially at Athens. Frei places the death of Protagoras in B.C. 411, assuming that Pythodorus accused him of teaching atheism during the government of the Four Hundred (Quest. Protag. p. 64), and accordingly assigns about B.C. 480 as the date of his birth.
That Protagoras had already acquired fame during his residence in Abdera cannot be inferred from the doubtful statement that he was termed by the Abderites λόγος, and by Democritus φιλοσοφία or σοφία (_Elian. etsr. Hist. 4:20; comp. Suid. s. vv. Πρωταγ. Δημόκρ., etc. Phavorinus, in Diog. Laert. 9:50, gives to Protagoras the designation of σοφία). He was the first who called himself a sophist and taught for pay (Plato, Protag. p. 349. a; Diog. Laert. 9:52). He must have come to Athens before B.C. 445, since, according to the statement of Heraclides Ponticus (Diog. Laert. 9:50), lie gave laws to the Thurians, or, what is more probable, adapted for the use of the new colonists, who left Athens for the first time in that year, the laws which had been drawn up at an earlier period by Charondas for the use of the Chalcidic colonies (for, according to Diod. 12:11, 3 and others, these laws were in force at Thurii likewise). Whether he himself removed to Thurii, we do not learn, but at the time of the plague we find him again in Athens, as he could scarcely have mentioned the strength of mind displayed by Pericles at the death of his sons in the way he does (in a fragment still extant, Plutarch, De Consol. ad Apoll.c. 33. p. 118, d) had he not been an eye-witness. He had also, as it appears, returned to Athens, after a long absence (Plato, Protag. p. 301, c), at a time when the sons of Pericles were still alive (ibid. p. 314, e; 329, a). A somewhat intimate relation between Protagoras and Pericles is intimated also elsewhere (Plut. Penicles, c. 36 p. 172, a). His activity, however, was by no means restricted to Athens. He had spent some time in Sicily, and acquired fame there (Plato, Hipp. Maj. p. 282, d), and brought with him to Athens many admirers out of other Greek cities through which he had passed (Plato, Protag. p. 315, a). He was accused of atheism by one of his scholars, and was consequently impeached for what he had written in his book On the Gods, which began with the statement, "Respecting the gods, I am unable to know whether they exist or do not exist" (Diog. Laert. 9:51, etc.). The impeachment was followed by his banishment (ibid. 9:52; Cicero, De Nut. Deolr. i, 23; Euseb. Praep. Evang. 14:19, etc.), or, as others affirm, only by the burning of his book (Philost. Vif. Soph. l.c.; Josephus, C. Apion. ii, 37; Sext. Emnp. Adv. Math. 9:56; Cicero, Diog. Laert. 11. cc.). Uelerweg says that it would seem Protagoras left for Sicily after his condemnation and was lost at sea (Hist. of Philos. i, 74).
Writings. — From the list of the writings of Protagoras, which Diogenes Laertius (9:55) doubtless borrowed from one of his Alexandrine authorities (he describes them as still extant, ἐστὶ τὰ σωζόμενα αὐτοῦ βιβλία ταῦτα: comp. Welcker's account of Prodicus, in his Kleine Sch7 ifjen. ii, 447, 465), and which he gives probably with his accustomed negligence, one may see that they comprised very different subjects: ethics (Περὶ ἀρετων and Περὶ τῶν οὐκ ὀρθῶς τοῖς ἀνθρώποις πρασσομένων, Περὶ φιλοτιμίας); politics (Περὶ πολιτείας, Περὶ τῆς ἐν ἀρχῇ καταστάσεως: comp. Frei, p. 182, etc.); o heforic (Α᾿ντιλογιῶν δύο, τέχνη ἐριστικῶν), and other subjects of different kinds (Προστακτικός, Περὶ μαθημάτων, Περὶ πάλης. Περὶ τῶν ἐν Αἵδου). The works which, in all probability, were the most important of those which Protagoras composed Truth (Α᾿λήθεια), and On the Gods (Περὶ θεῶν) — are omitted in that list, although in another passage (ix, 51) Diogenes Laertius refers to them. The first contained the theory refuted by Plato in the Theetetus (p. 161, c; 162, a; 166, c; 170, e), and was probably identical with the work on the Existent (Περὶ τοῦ ὄντος), attributed to Protagoras by Porphyry (in Euseb. Praep. Evang. 10:3, p. 468, Viger). This work was directed against the Eleatics (Πρὸς τοὺς ἕν τὸ ×ν λέγοντας), and was still extant in the time of Porphyry, who describes the argumentation of the book as similar to that of Plato, though without adding any more exact statements.
Doctrines. — With the peculiar philosophical opinions of Protagoras we obtain the most complete acquaintance from the Theoetetus of Plato, which was designed to refute it, and the fidelity of the quotations in which is confirmed by the much more scanty notices of Sextus Empiricus and others. The sophist started from the fundamental presupposition of Heracutus that everything is motion, and nothing besides or beyond it, and that out of it everything comes into existence; that nothing at any time exists, but that everything is perpetually becoming (Plato, Theoet. p. 156, 152: Sextus Empiricus inaccurately attributes to him matter in a perpetual state of flux, ὕλη ῥευστή, Pyrrhonm. Iyp. i, 217, 218). He then distinguished two principal kinds of the infinitely manifold motions, an active and a passive; but premised that the motion which in one concurrence manifested itself actively will in another appear as passive, so that the difference is. as it were, a fluctuating, not a permanent one (Thecet. p. 156, 157). From the concurrence of two such motions arise sensation or perception, and that which is felt or perceived, according to the different velocity of the motion; and that in such a way that where there is homogeneity in what thus meets, as between seeing and color, hearing and sound (ibid. p. 156), the definiteness of the color and the seeing, of the perception and that which is perceived, is produced by the concurrence of corresponding motions (ibid. 156, d; comp. 159, c). Consequently, we can never speak of Being and Becoming in themselves, but only for something (τινί), or of something (τινός), or to something (πρός, p. 160, b; 156, c; 152, d; Arist. Metaph. 9:3; Sext. Emp. Hyp. i, 216, 218). Therefore there is or exists for each only that of which he has a sensation, and only that which he perceives is true for him (Theoet. p. 152, a; comp. Crat.yl. p.
386; Aristocles, in Euseb. Praep. Evang. 14:20; Cicero, Acad. ii, 46; Sext. Emp. l.c. and Adv. Month. 7:63, 369, 388, etc.); so that as sensation, like its objects, is engaged in a perpetual change of motion (Theoet p. 152, b; Sext. Emp. Hyp. i, p. 217, fol.), opposite assertions might exist, according to the difference of the perception respecting each several object (Aristlletaph. 4:5; Diog. Laert. 9:5; Clem. Alex. Stron. v, 674, a; Senec. Epist. 88). The conclusions hitherto discussed, which he drew from the Heraclitean doctrine of eternal becoming, Protagoras summed up in the well-known proposition: 'The man is the measure of all things; of the existent, that they exist; of the non-existent, that they do not exist (Theoet. p. 152, a; 160, d; Cratyl. p. 385. e; Arist. Metaph. 10:1; 11:6; Sext. Emp. Adv. Math. 7:60; Pyrrhon. Hyp. i, 216; Aristocles, in Euseb. Price. Evanq. 14:20; Diog. Laert. 9:51); and understood by the man, the perceiving or sensation-receiving subject. He was compelled, therefore, likewise to admit that confutation was impossible, since every affirmation, if resting upon sensation or perception, is equally justifiable (Plato, Euthyd. p. 185, d, etc.; Isocr. Helene Enc. p. 231, Bekk.; Diog. Laert. 9:53); but, notwithstanding the equal truth and justifiableness of opposite affirmations, he endeavored to establish a distinction of better and worse, referring them to the better or worse condition of the percipient subject, and promised to give directions for improving this condition, i.e. for attaining to higher activity (Theoet. p. 167; comp. Sext, Emp. Hyp. i, 218). Already, before Plato and Aristotle (Metaph. 4:4; comp. the previously quoted passages), Democritus had applied himself to the confutation of this sensualism of Protagoras, which annihilated existtence, knowledge, and all understanding (Plutarch, Adv. Colot. p. 1109, a; Sext. Emp. Adv. Math. 7:389).
It is not every pleasure, but only pleasure in the beautiful, to which Protagoras, in the dialogue which bears his name (p. 351, b), allows moral worth; and he refers virtue to a certain sense of shame (αἰδώς) implanted in man by nature, and a certain conscious feeling of justice (δίκη), which are to serve the purpose of securing the bonds of connection in private and political life (ibid. p. 322, c, etc.); and, accordingly, explains how they are developed by means of education, instruction, and laws (p. 325, c, etc.; comp. 340, c). He is not able, however, to define more exactly the difference between the beautiful and the pleasant, and at last again contents himself with affirming that pleasure or enjoyment is the proper aim of the good (p. 354, etc.). In just as confused a manner does he express himself with respect to the virtues, of which he admits five (holiness, ὁσιότης —
and four others), and with regard to which he maintains that they are distinguished from each other in the same way as the parts of the countenance (ibid. p. 349, b; 329, c, etc.). As in these ethical opinions of Protagoras we see a want of scientific perception, so do we perceive in his conception of the Heraclitean doctrine of the eternal flow of all things, and the way in which he carries it out, a sophistical endeavor to establish, freed from the fetters of science, his subjective notions, setting aside the Heraclitean assumption of a higher cognition and a community of rational activity (ξυνὸς λόγος) by means of rhetorical art. That he was master of this in a high degree, the testimonies of the ancients leave indubitable. His endeavors, moreover, were mainly directed to the communication of this art by means of instruction (Plato, Protag. p. 312, c), to render men capable of acting and speaking with readiness in domestic and political affairs (ibid. p. 318, e). He would teach how to make the weaker cause the stronger (τὸν ἣττω λόγον κρείττω ποιεῖν, Aristot. Rhet. ii, 24; A. Gellius, V. A. v, 3; Eudoxus, in Steph. Byz. s.v. ῎Αβδηρα: comp. Aristoph. Nub. 113, etc., 245, etc., 873, 874, 879, etc.). By way of practice in the art he was accustomed to make his pupils discuss theses (communes loci) on opposite sides (antinomically) (Diog. Laert. 9:52, etc.; comp. Suid. s.v.; Dionys. of Halic., Isocr., Timon, in Diog. Laert. 9:52; Sext. Emp. Adv. ltath. 9:57; Cicero, Brut. 12); an exercise which is also recommended by Cicero (Ad Afftt. 9:4), and Quintilian (x, 5, § 10). The method of doing so was probably unfolded in his Art of Dispute τέχνη ἐριστικῶν; see above). But he also directed his attention to language, endeavored to explain difficult passages in the poets, though not always with the best success (Plato, Protag. p. 388, c, etc.; comp. respecting his and the opposed Platonic exposition of the wellknown lines of Simonides, Frei, p. 122, etc.). See Plato, Hipp. Haj. p. 282, c; Meno, p. 91, d; Theoet. p. 161, a; 179, a; Quintilian, 3, 1, § 10; Diogenes Laertius, 9:52, 50, etc.; Zeller, Philos. der Griechen, i, 244 sq.; Fisher, Beyginnings of Christianity, p. 117; Butler, Hist. of Ancient Philos. (see Index in vol. ii); Smith, Dict. of Gr. and Rom. Biog. and Mythol. s.v., which we have principally used; Ueberweg, Hist. of Philos. i, 73 sq.; Geist, De Protatgora Sophista (Giessen, 1827); Sprengel, in his Συναγωγὴ τεχνῶν (Stuttg. 1828), p. 152 sq.; Herbst, Protagoras in "Philos.-hist. Studien" (Hamb. 1832), p. 88 sq.; Krische, Forschungen, i, 130 sq.; Frei, Qucestiones Protagorece (Bonn, 1845); Weber, Qucest. Prot. (Marb. 1850); Bernays, in Rhein. Muts. f. Phil. 1850 (7), p. 464 sq.; Vitringa, De Prot. Vita et Phil. (Gron. 1853); Grote, Plato (Lond. 1865, 3 vols.); and his Hist. of
Greece, ch. 67; Mallet, Etudes Philosophiques, vol. ii; and the literature under Sophists, especially Schanz, Vorsokratische Philosophie (Gotting. 1867).