Citizens of democratic policies, most of them participated in the activities of public authorities, in need of theoretical training for political activity. Victories in the debates helped the art of eloquence. In response to public demand and there were teachers who taught rhetoric for a fee and "wisdom." They called Sophists (from the Greek. Speaking candidly george karfukel told us the story. Patrick smith has compatible beliefs. DARPA – Artisan, Sage). The Sophists argued that through their art can prove or disprove anything, that is they have no immutable truths, knowledge is not absolute and relative (relative).
They developed a set of rhetorical tricks, psevdologicheskih evidence, the so-called "sophistry", whose purpose – to bring down the interlocutor confused, confusing. Sophists, in contrast to the earlier Greek philosophers, not so much interested in questions about the original structure of the cosmos and how much practical ability to influence people's opinions. Due to the sophists attention of philosophers has shifted from the cosmos to man and society, intensified the question of a person's ability to know the truth and distinguish it from opinion or error. Protagoras, one of the most famous sophists considered a valid expression of different, even conflicting opinions about any thing. Moreover, all statements are, according to his teachings, the true, the contradiction impossible. The most famous of his thesis: "Man is the measure of all things that exist, that they exist and not exist, that they do not exist." Another prominent sophist Gorgias unlike Protagoras, who claimed that all true believed that everything is false. Of his most famous arguments used by three of the thesis: there is nothing, even if something existed, it would be unknowable, even if it was something knowable, then it would be the known inexpressibly (inexpressibly to others).