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Protagoras (c. 490 – c. 420 BC) was a pre-Socratic Greek philosopher and is numbered as one of the sophists by Plato. In his dialogue, Protagoras, Plato credits him with having invented the role of the professional sophist.
He also is believed to have created a major controversy during ancient times through his statement that, “Man is the measure of all things”, interpreted by Plato to mean that there is no absolute truth, but that which individuals deem to be the truth. Although there is reason to question the extent of the interpretation of his arguments that has followed, that concept of individual relativity was revolutionary for the time, and contrasted with other philosophical doctrines that claimed the universe was based on something objective, outside of human influence or perceptions.
Protagoras was born in Abdera, Thrace, in Ancient Greece. According to Aulus Gellius, he originally made his living as a porter, but one day he was seen by the philosopher Democritus carrying a load of small pieces of wood he had tied with a short cord. Democritus realized that Protagoras had tied the load together with such perfect geometric accuracy that he must be a mathematical prodigy. Democritus promptly took him into his own household and taught him philosophy. Protagoras became well known in Athens and even became a friend of Pericles.
The dates of his lifetime are not recorded, but extrapolated from writings that have survived the ages. In Protagoras Plato wrote that, before a gathering of Socrates, Prodicus, and Hippias, Protagoras stated that he was old enough to be the father of any of them. This suggests a birth date of not later than 490 BC. In the Meno he is said to have died at approximately the age of 70, after 40 years as a practicing Sophist. His death, then, may be presumed to have occurred circa 420 BC.
Plutarch wrote that Pericles and Protagoras spent a whole day discussing an interesting point of legal responsibility, that probably involved a more philosophical question of causation: “In an athletic contest a man had been accidentally hit and killed with a javelin. Was his death to be attributed to the javelin, to the man who threw it, or to the authorities responsible for the conduct of the games?”
Protagoras was skeptical about the application of theoretical mathematics to the natural world; he did not believe they were really worth studying at all. According to Philodemus, Protagoras said that “The subject matter is unknowable and the terminology distasteful”.
Protagoras also was known as a teacher who addressed subjects connected to virtue and political life. He especially was involved in the question of whether virtue could be taught, a commonplace issue of fifth century BC Greece, that has been related to modern readers through Plato’s dialogue. Rather than educators who offered specific, practical training in rhetoric or public speaking, Protagoras attempted to formulate a reasoned understanding, on a very general level, of a wide range of human phenomena, including language and education.
He also seems to have had an interest in “orthoepeia”—the correct use of words, although this topic is more strongly associated with his fellow sophist Prodicus. In his eponymous Platonic dialogue, Protagoras interprets a poem by Simonides, focusing on the use of words, their literal meaning, and the author’s original intent. This type of education would have been useful for the interpretation of laws and other written documents in the Athenian courts. Diogenes Laërtius reports that Protagoras devised a taxonomy of speech acts such as assertion, question, answer, command, etc. Aristotle also says that Protagoras worked on the classification and proper use of grammatical gender.
Protagoras is credited with the philosophy of relativism, which he discusses in his work, Truth (also known as Refutations). Although knowledge of his work is limited, discussions of Protagoras’ relativism is based on one of his most famous statements: “Man is the measure of all things: of the things that are, that they are, of the things that are not, that they are not.” By this, Protagoras meant that each individual is the measure of how things are perceived by that individual. Therefore, things are, or are not, true according to how the individual perceives them. For example, Person X may believe that the weather is cold, whereas Person Y may believe that the weather is hot. According to the philosophy of Protagoras, there is no absolute evaluation of the nature of a temperature because the evaluation will be relative to who is perceiving it. Therefore, to Person X, the weather is cold, whereas to Person Y, the weather is hot. This philosophy implies that there are no absolute “truths”. The truth, according to Protagoras, is relative, and differs according to each individual.
Plato ascribes relativism to Protagoras and uses his predecessor’s teachings as a foil for his own commitment to objective and transcendent realities and values. Plato ascribes to Protagoras an early form of what today, John Wild would label, phenomenalism. That being an assertion that something that is, or appears for a single individual, is true or real for that individual.
Protagoras clearly explained in his work, Theaetetus, however, that some of such controversial views may result from an ill body or mind. He stressed that although all views may appear equally true, and perhaps, should be equally respected, they certainly are not of equal gravity. One view may be useful and advantageous to the person who has it, while the perception of another may prove harmful. Hence, Protagoras believed that the sophist was there to teach the student how to discriminate between them, i.e., to teach virtue.
Protagoras also was a proponent of agnosticism. Reportedly, in his lost work, On the Gods, he wrote: “Concerning the gods, I have no means of knowing whether they exist or not, nor of what sort they may be, because of the obscurity of the subject, and the brevity of human life.” (DK80b4) According to Diogenes Laërtius, the outspoken, agnostic position taken by Protagoras aroused anger, causing the Athenians to expel him from the city, and all copies of his book were collected and burned in the marketplace. The deliberate destruction of his works also is mentioned by Cicero.
Burnet notes that even if some copies of the Protagoras books were burned, enough of them survived to be known and discussed in the following century.
Guthrie, W. K. C., The Sophists. New York: Cambridge University Press (May 27, 1977).
Protagoras of Abdera: The Man, His Measure. Brill, 2013.