Protagoras
Pre-Socratic sophist who argued that truth is relative to each individual.
Protagoras (c. 490–c. 420 BCE) was a pre-Socratic Greek philosopher and rhetorical theorist from Abdera, Thrace, located opposite the island of Thasos. He is recognized as one of the sophists by Plato, who also credited him with inventing the role of the professional sophist. According to Aulus Gellius, Protagoras originally worked as a porter; the philosopher Democritus, observing him tying a load of wood with remarkable geometric precision, concluded he was a mathematical prodigy and took him on as a student. Protagoras later became well known in Athens and a friend of Pericles. Plutarch recounts that Pericles and Protagoras spent an entire day debating a legal question of causation: after a man was accidentally killed by a javelin during an athletic contest, they considered whether responsibility lay with the javelin, the thrower, or the officials running the games. Protagoras is most famous for his statement, "Man is the measure of all things," from his book *Truth*. This was interpreted by Plato as denying objective truth, but Protagoras likely meant that each person’s unique history and experiences shape their judgments about what is good, bad, beautiful, or unjust. He argued that accepting this individual relativity—respecting others’ valid opinions even when they differ from one’s own—was essential for a community to engage in open, democratic debate. He taught subjects concerning virtue and political life, particularly whether virtue could be taught, and claimed to instruct in managing one’s household and contributing effectively to public affairs through word and action. He also worked on the classification of speech acts, such as assertion and question, and on grammatical gender. Despite being mentored by Democritus, Protagoras was skeptical of theoretical mathematics, arguing that perceptible lines do not match geometric ideals and that the subject was unknowable and its terminology distasteful. He died at approximately age 70, around 420 BCE, after 40 years as a practicing sophist.
- field
- Philosophy, rhetoric, sophistry
- nationality
- Greek (from Abdera, Thrace)
- known_for
- Man is the measure of all things; relativism; professional sophist
Lore & Background
According to Aulus Gellius, he originally worked as a porter until the philosopher Democritus observed him tying a load of wood with such geometric precision that he took Protagoras into his household to teach him philosophy. Protagoras became well known in Athens and a friend of Pericles. Protagoras taught subjects related to virtue and political life, claiming to teach 'the proper management of one's own affairs, how best to run one's household, and the management of public affairs.' He worked on the correct use of words (orthoepeia), devised a taxonomy of speech acts, and classified grammatical gender. He also wrote a book titled Truth (or Refutations), in which he made his famous statement about man being the measure of all things. He argued that on any matter there are two opposing arguments (logoi) and was criticized by Aristotle for claiming 'to make the weaker argument stronger.'
Reader's Guide
Protagoras's significance lies in his radical relativism, encapsulated in the claim that 'Man is the measure of all things.' He appears to have meant that each person's own history, experiences, and expectations determine their judgments about truth, so that there is no objective truth independent of the individual. This concept was intended to be provocative and was criticized by Plato and other philosophers who insisted on an objective grounding for reality and truth. However, Protagoras argued that respecting others' opinions, even when they differ from one's own, is necessary for a community to base itself on open, democratic debate. His legacy includes influencing later skeptical and phenomenological traditions; Eusebius, quoting Aristocles of Messene, places him in a line of philosophy from Xenophanes to Pyrrhonism. Plato and Aristotle both argued against his relativism, claiming it exempted Protagoras from his own theory. Despite the loss of most of his writings, Protagoras remains a pivotal figure in the history of philosophy for challenging the notion of absolute truth and for formalizing the role of the professional sophist in Athenian intellectual life.
Did You Know?
- Protagoras was originally a porter before being discovered by Democritus, who taught him philosophy.
- He spent a whole day with Pericles discussing legal responsibility in a case where a man was killed by a javelin during an athletic contest.
- He devised a taxonomy of speech acts including assertion, question, answer, and command.
- He was one of the first to take part in rhetorical contests at the Olympic games.
Frequently Asked Questions
What is Protagoras's most famous philosophical claim?
His signature statement, 'Man is the measure of all things,' asserts that each person's perception is the ultimate standard of truth for that individual. This introduced a radical form of individual relativism that generated centuries of debate.
What was Protagoras's role in ancient Greek society?
Plato credits him with establishing the profession of the sophist—someone who taught rhetoric and argumentation for payment. In that capacity, he traveled among Greek city-states offering instruction in persuasive speech.
Why does Protagoras matter in the history of philosophy?
His relativist doctrine challenged the idea of objective truth and forced later thinkers like Plato to define their positions in opposition to his. He also helped shape the tradition of rhetorical education that became central to Greek intellectual culture.
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