170 184 ancient aristotle byperiod contributionsinconceptoftruthplato contributionsinconceptoftruthprotagoras contributionsinconceptofvaluesplato contributionsinconceptofvaluesprotagoras democritus earlyworksto1800 ethics greece herodotus history individualphilosophers occident philosophy philosophy(general) plato pluralism politicalscience protagoras(plato) relativity separateworks socrates sophists(greekphilosophy) sophocles symmetry thirdperiod truth values virtue