Philosophy first emerged in the sixth century BCE on the Greek island of Miletus. The first philosophers, known as the Presocratics because their thought was untouched by Socrates’ influence, focused on questions of natural science, trying to explain the world through physical explanations, rather than the existing mythological explanations for the existence of the world, the universe, and matter. In the fifth century BCE, two tremendous political upheavals cast traditional Greek values into question and thrust issues of ethics into the hands of the philosophers. From 431 to 404 BCE Athens and Sparta were engaged in the Peloponnesian War, which Athens eventually lost. The ravages of war cast doubt on the martial virtues of Homeric heroes, and the growth of democracies, especially in Athens, called for new civic virtue: the ability to speak persuasively in the assemblies and law courts became more valuable than warcraft.

A new class of individuals emerged in this changed Athenian climate: the Sophists, itinerant teachers who would offer instruction in nearly any subject if the student was willing and able to pay a fee. Their teachings capitalized on a void left by the ancient myths and religion, which were falling out of fashion as Greek civilization moved toward a more rational worldview. The Sophist taught that values are relative, and that the only measure of who is right is who prevails. Many argued that there were no such things as right and wrong—that objective moral standards did not exist. Some Sophists denied any possibility of objective truth and scoffed at the idea of objective knowledge. They claimed that morality is a convention imposed by the rulers of societies upon their subjects. 

In his writings, Plato was determined to set Socrates apart from the Sophists, and many of his dialogues have Socrates showing the emptiness of Sophists teachings. One of the great differences between Socrates and the Sophists is that the Sophists charged a fee for their services, and Socrates’ poverty is strong evidence that he clearly did not profit from teaching. Socrates contrasts himself from the Presocratics by never claiming expertise or teaching Presocratic philosophy himself and, indeed, all of his teachings remained exclusively in the human realm, dealing with questions of ethics and virtue. One of his great contributions to philosophy, in fact, is the introduction of ethical questions, and the dismissal of Presocratic interest in cosmology. 

Socrates’ confession that he lacks any kind of expertise in any field whatsoever is central to his philosophy. It sets him apart from both the Sophists and the Presocratics. Teachers from these two groups both claimed that through experience, inspiration, or investigation, they had gained access to special knowledge that could be taught. Socrates, on the other hand, never makes any particular claims to knowledge, and his inquiries tend to show the ignorance of his interlocutors rather than his own expertise.

Plato took over this mission when Socrates died. Thus, throughout his works, Plato gives a rather unkind picture of the Sophists, painting them as generally shallow thinkers who taught budding politicians to overcome sound reasoning with shoddy reasoning by means of flowery rhetoric. Plato also combatted the Sophists’ other skeptical claims: their avowal that there is no such thing as objective truth, no possibility of objective knowledge.