The development of thought and society in the democratic Athens of the fifth century b.c.e. and the increasing sophistication of society inspired and benefited a class of peripatetic philosopher-teachers who became known as the Sophists. There were numerous Sophists practicing their profession, and around 30 of them are particularly well known, including Protagoras, Isocrates, Gorgias, and Thrasymachus.

Their teachings included not just speculation as to the nature and substance of the universe but also rhetoric and the art of life and politics. The education they offered was, therefore, a practical one and suited to contemporary life in Athenian society. Subsequent philosophers such as Socrates and Plato established permanent schools, and their education was more focused on the search for truth.

Adherents of these later schools used the term sophist as a term of abuse to imply that the method of sophism deliberately failed to engage with the truth and used philosophical methods falsely to win arguments in an underhanded way. However, in the fifth century b.c.e. the term was not assigned to any one particular school of thought.

Perhaps the greatest of the Sophists was Protagoras of Abdera, who was active in approximately 450–440 b.c.e. He traveled from city to city teaching for pay. His particular area of expertise was in the practice of arete, which involves the development of political and rhetorical skill.

He believed that because there was a subjective, human element involved in every judgment or decision, it was impossible to reach ultimate truth about any external phenomenon. Opposing statements could be made about anything, for example, the existence of the gods, without any means of determining what was true because of the imperfection of the human mind (or the shortness of life) and the complexity of issues involved.

He observed: "Man is the measure of all things, of the existence of the things that are and the non-existence of the things that are not". In other words, final or ultimate truth could not be known.

His fellow Sophist Gorgias, meanwhile, argued (perhaps satirically) that nothing exists, or if it does exist it cannot be known, or if it could be known it could not be communicated to anyone else. These forms of arguments were in opposition to the Eleatic school, which was then flourishing in the southern Italian colony of Elea and was best represented by the thought of Parmenides and his pupil Zeno.

Eleaticism featured the monistic belief that thought, expression, and existence all coalesced into being. The Sophists found this to be of little practical value in the Athens of Pericles, where they mostly congregated and where the limits of personal infl uence were being extended for those not of noble birth.

Exactly to what extent individual doctrines can be ascribed to individual Sophists is difficult to ascertain because knowledge of those teachings is mediated by the writings of Plato, whose dialogues feature debates between Sophists and more modern thinkers such as Socrates but whose audience would have been expected to know in some detail what individual Sophists taught and does not itemize those beliefs in detail. Other sources of early Sophist thought include the "Exhortation to Philosophy" by Iamblichus (third century c.e.) and the "Dissoi Logoi" of Sextus Empiricus (third century c.e.).

A particular use of antilogic employed by Sophists was the opposition of custom and nature. Possibly employing a line of thought that had been developed earlier, Sophists aimed to contrast the existing laws of society with the higher laws of nature, either because laws were not sufficiently rigorous to deal with the nature of humanity or, more commonly, to free people from unwanted restrictions.

This form of political discourse represented a feature that could be characterized as an attack on public morals, and so Socratic thinkers claimed it. A number of Sophists were brought to trial for impious teaching, not least because their ideas challenged the existing social order.

Critias, for example, taught that the gods were invented by the powerful elites of society to intimidate and help tyrannize the rest of society. Prodicus suggested a sociological approach to the development of the gods of Olympus, while Protagoras, as has been shown, refused to accept that the existence of the gods could ever be known.

The Sophists were important as part of the development of education, politics, and philosophy. They represented an early example of the professional educator and the political tutor, one who tempered in his students the desire to succeed with the importance of virtue.