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Protagoras of Abdera


Protagoras of Abdera in Thrace, most famous of the Sophists, was born not later than 490 BCE and probably died soon after 421 BCE. According to Plato, he was the first to declare himself a professional Sophist. He went from city to city in the Greek world, offering instruction in return for money, and he undertook above all to train young men in the art of politics. He was well known in Athens, where he enjoyed the friendship of Pericleshe produced a theoretical basis for Periclean democracy and was asked by Pericles to draft the constitution for the new colony of Thurii in 443 BCE. He made contributions to grammatical and rhetorical theory, and his views on religion provoked charges of impiety against him in the courts, which led to his exile from Athens at the end of his life and to the public burning of at least one of his books.

His writings were numerous and included "On Truth," "On the Gods," and "Antilogic" (or "Antilogies"). Later writers probably took their information about him mainly from the accounts of Plato, Aristotle, and Sextus Empiricus, but one of his works was read by Porphyry in the third century CE, and in the Hellenistic period he was regarded as sufficiently important for his statue to be set up, together with those of Plato, Aristotle, and other thinkers, in the Serapeum at Memphis in Egypt.

Since the time of Plato, Protagoras's main doctrines have been regarded as possessing considerable philosophical interest, even by those who deny philosophical importance to the Sophists in general; but very divergent interpretations have been propounded. With no surviving works and virtually no fragments, interpretation must depend upon the assessment of the evidence of Plato, Aristotle, and Sextus Empiricus. In what follows, the view is taken that Plato in the Theaetetus correctly states the basic position of Protagoras and then proceeds to distinguish certain possible developments of this position not held by Protagoras. The basic position was independently understood in the same way by both Aristotle and Sextus Empiricus, each of whose information was not simply derived from the Theaetetus. This would be denied by some scholars.


The starting point must be the famous contention that "man is the measure of all things, of things that are that [or 'how'] they are and of things that are not that [or 'how'] they are not." Theodor Gomperz maintained that "man" is to be understood collectively in the sense of "mankind as a whole" or "the human race." But against this, the evidence of the Theaetetus 152ab seems to show conclusively that it is individual men that Protagoras had in mind in the first instance, although, as will be seen, his theory is capable of easy extension to groups of men, and he probably made this extension himself.

According to Plato's example in the Theaetetus, when the same wind appears cold to one person and warm to another person, then the wind is warm to the person to whom it appears warm and is cold to the person to whom it seems cold. It follows that all perceptions are true and the ordinary view is mistaken, according to which, in cases of conflict, one person is right and the other person is wrong about the quality of the wind or of anything else. This clearly was the position held by Protagoras, but it is not clear exactly how he came to this view. It is often held that his position is a kind of subjective idealism similar to that of Bishop Berkeley, according to which qualities in a thing are for the person to whom they seem, so long as they seem to him, but have no existence independent of their seeming.

Against this view, Sextus Empiricus is explicit: All qualities perceived by different persons are actually present in matter. Sextus's introduction of matter may well be anachronistic, but his account suggests an alternative view, accepted by F. M. Cornford among others, according to which opposite qualities are copresent in objects, and in cases of conflict of perceptions between two persons, what happens is that we have a sort of selective perceptionone person perceives one quality and the other its opposite, both qualities being present in the situation, waiting to be perceived, as it were, independently of any actual perceiving by a subject. This view seems to have the support of Aristotle, who always treats Protagoras's doctrine as involving the denial of the principle of contradiction, and the view coincides with incidental pointers in Plato's account ("the same wind"152b; "perception, then, is always of something that is"152c). It is true that in the "secret doctrine" attributed to Protagoras by Plato (152cff.) the independent status of sense objects is undermined, but the fact that this is presented as a secret doctrine is surely conclusive evidence that it was a doctrine not publicly associated with Protagoras.

The "man-measure" doctrine is presented by Plato in the first instance as a doctrine about perception of sensible qualities. But it is clear that Plato supposed that for Protagoras it also applied to moral and aesthetic qualities such as "just" and "beautiful." It is especially in these cases that the extension of the doctrine to groups of people was made by Protagoras"whatever seems just to a city is just for that city so long as it seems so." Probably Protagoras did not extend his doctrine to apply to all judgments; this was done immediately by his opponents in the famous peritrope, or "turning of the tables": Let us suppose that whatever seems true to any person is true for the person to whom it seems so. If this is the doctrine of Protagoras, then Protagoras will hold that those who hold that Protagoras's theory is false are holding the truth (Theaetetus 171a). But Plato points out that if Protagoras could pop his head up through the ground, he would surely have an answer to this objection.

At the very least, Protagoras was clear about one point. In the case of conflict about perceived qualities all perceptions are true. But some perceptions are better than others, for example, the perceptions normally found in a healthy man as distinct from those found in a man who is ill. It is the function of a doctor, Protagoras held, to change a man who is ill so that his perceptions become those of a man who is well. Likewise, in moral, political, and aesthetic conflicts it is the function of the Sophist as a teacher to work a change so that better views about what is "just" and "beautiful" will seem true to the "patient"better, that is, than those that previously seemed true to him. All the "patient's" views are equally true, but some are better than others.

There is nothing to suggest that by "better" Protagoras meant what will seem better. Quite the contrary. Better views are views that have better consequences, and consequences which are better are so as a matter of fact, independently of whether a person thinks them better or not. In other words, Protagoras here made an exception to his man-measure doctrine. There is every reason to suppose that he would have excepted the class of judgments about the consequences of judgments from his principle. Indeed, there is no actual evidence in any ancient author that Protagoras himself ever applied his doctrine to statements other than those about perceived qualities and moral and aesthetic qualities treated on the same plane as visually perceived qualities. What probably happened was that he propounded his doctrine in certain general statements such as "whatever seems to anyone is so for that person," without adding the qualifications that he really intended; thus he gave a handle to his enemies, which enabled them to apply the peritrope and similar objections.

The above account rests primarily upon Plato's Theaetetus. To it may be added evidence from other sources. According to Diogenes Laërtius, Protagoras was the first to propound the theory that there are two logoi, or accounts, to be given about everything. This has sometimes been treated as simply the now familiar rhetorical doctrine that "there are two sides to every question." But this theory was used as a method of argument, and it should probably be related to the man-measure doctrine and to what Plato called "Antilogic," the probable title of one of Protagoras's treatises. In conflicts about perceived qualities, and also moral and aesthetic qualities, there might seem room for an infinite variety of "seemings," but if we take any one as a starting point, for instance, that the wind seems warm, all other seemings may be expressed as the negative of this, namely "not-warm." This was clearly the way in which Plato tended to regard phenomenaas did the antilogicians, toonamely, as always being both "warm" and "not-warm." In this view, Plato was probably following Protagoras. It is possible that Protagoras associated with the two-logoi principle the prescription attributed to him by Aristotle "to make the lesser [or 'the weaker'] argument the stronger." This may have been what the Sophist was expected to do when altering a man's opinions for the better.

Social Theory

In Plato's dialogue Protagoras we are given a coordinated theory of the Sophist in relation to society and of a possible theoretical basis for a Periclean-style democracy. All is completely consistent with the positions attributed to Protagoras in the Theaetetus. When Protagoras professes to make men good citizens, Socrates objects that while the Athenians call in experts to advise on technical matters, they regard all citizens as capable of advising them on matters relating to the city. This seems to imply that Athenian democracy leaves no place for expert instruction in citizenship. Protagoras replies with a myth followed by a nonmythical exposition that while all men share in the qualities that make good citizens, they do not do so by nature but acquire these qualities by instruction and by practice. These qualities are beliefs and opinions about what is just and right. In a sense, the whole community teaches its members about these matters, and so all are rightly consulted about political matters. But the expert teacher, such as the Sophist Protagoras, can improve opinions on such matters, whether it be in the case of an individual or in the case of a whole community.

Other Views

Protagoras's doctrines ranged beyond the topics discussed above to cover physical and mathematical problems as well, but it is no longer possible to state his actual teachings on these problems. He seems to have held that a tangent touches a circle not only at one point, but at more than one, clearly arguing from visual experience of drawn lines. Parmenides had rejected the world of seeming in favor of his world of being; Protagoras took the opposite path and attempted to expound a world in which all appearances were true and where there was nothing outside or beyond what appeared. This involved the copresence of opposed and contradictory qualities at many points. Protagoras was prepared to accept and explain this copresence through his "man-measure" principle, either on the basis of a theory of subjective idealism or, more probably, on the basis of a conception of a phenomenal world actually composed of opposites (a conception typical of the pre-Socratics). This conception seemed to Plato to be substantially correct for the phenomenal world, hence his great interest in Protagoras. But Plato felt that this view made it impossible to give any account or explanation of phenomena, and to be able to give an explanation seemed to him essential.

Diogenes Laërtius says that for Protagoras the soul is nothing apart from its perceptions. This suggests a phenomenalistic view of the soul as well as of everything else. Diogenes' account may be correct, although doubts have been cast upon it. If it is correct, however, it probably was not intended to imply any doctrine like the modern theory of neutral monism, but simply to deny the existence of any "submerged," or nonphenomenal, element in the soul.

See also Ethical Relativism; Sophists.


texts and translations

Gagarin, Michael, and Paul Woodruff. Early Greek Political Thought from Homer to the Sophists. Cambridge, U.K.: Cambridge University Press, 1995.

Sprague, R.K., ed. The Older Sophists; a Complete Translation by Several Hands of the Fragments in die Fragmente der Vorsokratiker, ed. by Diels-Kranz. Columbia: University of South Carolina Press, 1972.

Fragments and testimonia of Protagoras' work may be found in H. Diels and W. Kranz, eds., Fragmente der Vorsokratiker, 10th ed. (Berlin, 1961), Vol. II. A. Capizzi, Protagora (Florence, 1955), is probably the best full discussion, and it includes some material not in Diels and Kranz.


Bett, R. "The Sophists and Relativism." Phronesis 34 (1989): 139169.

Classen, J. "Protagoras' Aletheia." In The Criterion of Truth, Essays Written in Honour of George Kerferd, edited by P. Huby and G. Neal. Liverpool: Liverpool University Press, 1989.

Guthrie, W. K. C. The Sophists. Cambridge, U.K.: Cambridge University Press, 1971.

Kerferd, G. B. "Plato's Account of the Relativism of Protagoras." Durham University Journal 42 (1949): 2026.

Kerferd, G. B. "Protagoras' Doctrine of Justice and Virtue in the 'Protagoras' of Plato." Journal of Hellenic Studies 73 (1953): 4245.

Kerferd, G. B. The Sophistic Movement. Cambridge, U.K.: Cambridge University Press, 1981.

Schiappa, E. Protagoras and Logos: A Study in Greek Philosophy and Rhetoric. Columbia, SC: University of South Carolina Press, 1991.

Vlastos, G. "Introduction." In Plato's Protagoras, translated by M. Ostwald. Indianapolis/New York: Bobbs-Merrill, 1956.

G. B. Kerferd (1967)

Bibliography updated by Paul Woodruff (2005)

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