Protagoras (; ; ) was a pre-Socratic Greek philosopher and rhetorical theorist. He is numbered as one of the sophists by Plato. In his dialogue Protagoras, Plato credits him with inventing the role of the professional sophist. Protagoras also is believed to have created a major controversy during ancient times through his statement that, "Man is the measure of all things," interpreted (possibly wrongly, since he disagreed) by Plato to mean that there is no objective truth; Protagoras seems to have meant that each person's own personal history, experiences and expectations, developed over their lifetime, determine their judgments, opinions, and statements regarding "truth" (which is the title of the book in which Protagoras made this statement). When a person makes a judgment about a certain thing—good or bad or beautiful or unjust—that person will differ from other people's judgments because their experience has been different. This concept of individual relativity was intended to be provocative; naturally, it drew fire from Plato and other philosophers, contrasting with both popular opinion and other philosophical doctrine that reality and its truth must have an objective grounding. But it was part of Protagoras' point that the statement is somewhat counterintuitive. He argued that believing that others' opinions about the world are valid and must be respected, even if our own experience of truth is different, is necessary for a community to base itself and its decisions on open, democratic debate. Biography Protagoras was born in Abdera, Thrace, opposite the island of Thasos (today part of the Xanthi regional unit). According to Aulus Gellius, he originally made his living as a porter, but one day he was seen by the philosopher Democritus carrying a load of small pieces of wood he had tied with a short cord.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 life 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