Plato

Protagoras 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 or teacher of virtue. He is also believed to have created a major controversy during ancient... times through his statement that "man is the measure of all things". This idea was revolutionary for the time and contrasted with other philosophical doctrines that claimed the universe was based on something objective, outside the human influence. 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 According to Aulus Gellius, he originally made his living as a porter, but one day he was seen by the philosopher Democritus carrying a load of small pieces of wood tied with a short cord. Democritus discovered that Protagoras had tied the load himself with such perfect geometric accuracy that it revealed him to be a mathematic prodigy. He immediately took him into his own household and taught him philosophy.
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Socrates was a classical Greek Athenian philosopher. Credited as one of the founders of Western philosophy, he is an enigmatic figure known chiefly through the accounts of later classical writers, especially the writings of his students Plato and Xenophon, and the plays of his contemporary... Aristophanes. Many would claim that Plato's dialogues are the most comprehensive accounts of Socrates to survive from antiquity. Through his portrayal in Plato's dialogues, Socrates has become renowned for his contribution to the field of ethics, and it is this Platonic Socrates who also lends his name to the concepts of Socratic irony and the Socratic method, or elenchus. The latter remains a commonly used tool in a wide range of discussions, and is a type of pedagogy in which a series of questions are asked not only to draw individual answers, but also to encourage fundamental insight into the issue at hand.
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Heraclitus of Ephesus was a pre-Socratic Greek philosopher, a native of the Greek city Ephesus, Ionia, on the coast of Asia Minor. He was of distinguished parentage. Little is known about his early life and education, but he regarded himself as self-taught and a pioneer of wisdom. From the lonely... life he led, and still more from the riddling nature of his philosophy and his contempt for humankind in general, he was called "The Obscure" and the "Weeping Philosopher". Heraclitus is famous for his insistence on ever-present change in the universe, as stated in the famous saying, "No man ever steps in the same river twice" . He believed in the unity of opposites, stating that "the path up and down are one and the same", all existing entities being characterized by pairs of contrary properties. His cryptic utterance that "all entities come to be in accordance with this Logos" has been the subject of numerous interpretations.
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Aristophanes , son of Philippus, of the deme Cydathenaus, was a comic playwright of ancient Athens. Eleven of his 40 plays survive virtually complete. These, together with fragments of some of his other plays, provide the only real examples of a genre of comic drama known as Old Comedy, and they... are in fact used to define the genre. Also known as the Father of Comedy and the Prince of Ancient Comedy, Aristophanes has been said to recreate the life of ancient Athens more convincingly than any other author. His powers of ridicule were feared and acknowledged by influential contemporaries; Plato singled out Aristophanes' play The Clouds as slander contributing to the trial and execution of Socrates although other satirical playwrights had also caricatured the philosopher. His second play, The Babylonians , was denounced by the demagogue Cleon as a slander against the Athenian polis.
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