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Compiled by Anthony Harrison-Barbet


(c. 490 — 420 B.C.)



Protagoras was born in Abdera, an Ionian colony in Thrace. In 444 he drafted the constitution of a new Athenian colony for the great statesman Pericles. It is said that he was later exiled from Athens, and his books (which included On Truth and On the Gods) burned, because of his alleged impiety towards the popular gods. His writings have not survived, and we rely on Plato, Aristotle, and Sextus Empiricus for our knowledge of his philosophy.



[1] While the majority of presocratic philosophers were concerned to work out cosmologies and metaphysical accounts of the world, the Sophists were essentially itinerant professional educators in a wide range of subjects in addition to philosophy. Their main aim was to train their pupils to achieve arete (roughly, 'excellence') [a] and thereby to be 'successful' in life; and they employed a variety of techniques (the art of rhetoric) to encourage acceptance of a particular conclusion — or its opposite. As Protagoras said, "On every topic there are two arguments contrary to each other". The Sophists varied greatly, many being superficial and viewed with suspicion and even hostility by their contemporaries. Others, however, made important contributions to epistemology, to language and its relation to thinking and reality, as well as to ethics and political theory. Protagoras' philosophy is summed up in his claim that "A human being is the measure of all things, of things that are as to how they are, and of things that are not as to how they are not" [fr. 1 in Sextus, Against the Dogmatists] — a 'relativist' view [b] which all Sophists generally agreed with.



[2] As applied to our sense experiences Protagoras' doctrine means that, for example, if honey seems sweet to some people but bitter to others then it is sweet to the former and is bitter to the latter. There cannot therefore be any objective knowledge or truth concerning what things are 'really' like, that is, knowledge which is the same for everybody and open to all. All qualities are attributable to convention ['law', nomos] and not to 'nature' (phusis) [a].



[3] Protagoras's relativism in ethics is implicit in his recognition that people in other communities often held different religious beliefs and acted in accordance with different moral codes. This suggested to him that morality is a matter of social 'convention' rather than being grounded in 'nature' [a]. But while this might rule out the possibility of an absolute ethic applicable to all societies, some degree of objectivity is preserved in so far as a particular standard is accepted and shared by the individual members of a given community.



Protagoras was perhaps the greatest of the Sophists, and, despite the alleged errors of his thought, was admired greatly by Plato. While there can be no doubt that Protagoras said that man is the measure of all things, there has been considerable argument as to whether (1) he was referring to societies rather than to individual men, and (2) he intended it to apply in ethics as well as to knowledge. A reasonable compromise position would be that in his epistemology it is indeed the individual man who is the measure but in his ethics it is the society which sets the standard. His ethical relativism, however, is consistent with objectivism in so far as a particular relativist standard is shared by all individual members of that community; and it may therefore be called 'cultural' relativism. Protagoras was thus actually rather traditional, stressing the need for commitment to the values and beliefs of one's own society. Nevertheless, while individual relativism in perception might be compatible with communal or cultural relativism in ethics, there could still be a tension if his statement about the possibility of 'contrary arguments' on every topic were taken literally.



R. D. McKirahan, Philosophy before Socrates, ch. 18.

G. B. Kerferd, The Sophistic Movement.

G. B. Kerferd (ed.), The Sophists and their Legacy.

See also Plato's Protagoras and Theaetetus. [For editions see under Plato.]





[1a] Virtue/ excellence








[1b 2a] Relativism — knowledge (sense-perception); all qualities due to nomos ('convention')








[6b 7b]

[secs 16 17]





[3a; cf. 2a] Relativism in ethics; 'convention' versus 'nature'










[11e 12a]

[18a b 19c]

[2a d]