Greek philosophers
Próthagoras of Abdera
Próthagoras of Abdera was a Greek philosopher and orator. He was born in 481 BC (Abdera in Thrace) and died in 410 BC. He is considered the most famous of the first generation of sophists.
In his youth, Próthagoras is said to have been a pupil of Democritus. He became famous for the statement "the measure of all things is man - those that are, that are, and those that are not, that are not".
The crater Protagoras on the inverted side of the moon was named after him.
Protagoras of Abdera was also active in Athens, where he founded a school of philosophy. Here he befriended Pericles, with whom he discussed legal issues extensively. Later, however, he was banished from Athens (supposedly for impiety) because in his treatise On the Gods he claimed that he could not know whether they existed or not and recognized only the usefulness of religion to society. On his way to exile in Sicily, he drowned.
His works have not survived, but we have information about them from Plato, Aristotle, and Sextus Empiricus. He was one of the first to address the proper use and precise meaning of words. This was mainly in connection with the interpretation of laws.
Very often Próthagoras of Abdera is taken as a contrast to Socrates.