Greek rhetoric is commonly traced to Corax of Syracuse, who first formulated a set of rhetorical rules in the fifth century BC. His pupil, Tisias, was influential in the development of the rhetoric of the courtroom, and by some accounts was the teacher of Isocrates. Within two generations, rhetoric had become an important art, its growth driven by the social and political changes, such as democracy and the courts of law.
The demand for rhetorical training was so high that a number of philosophers and teachers set up their own schools to train orators. Among these were the Sophists, which included such teachers as Isocrates and Gorgias. These schools proved to be a lucrative enterprise, and later attracted less reputable characters.
Isocrates was born to a wealthy family (his father owned a successful flute factory) and received a fine education. He studied with Gorgias and possibly Socrates, among others. After the Peloponnesian War, Isocrates' family lost its wealth, and Isocrates was forced to earn a living.
Isocrates' professional career is said to have begun as a logographer, or a hired courtroom speech writer. Around 392 BC he set up his own school of rhetoric, and proved to be not only an influential teacher, but a shrewd businessman. His fees were unusually high, but he managed to attract more students than any other school. As a consequence, he amassed a considerable fortune.
Isocrates' program of rhetorical education stressed the ability to use language to address practical problems, cases where absolute truth was not obtainable. He also stressed civic education, training students to serve the state. Students would practice composing and delivering speeches on various subjects. He considered natural ability and practice to be more important than rules or principles of rhetoric. Rather than delineating static rules, Isocrates stressed "fitness for the occasion," or kairos (the rhetor's ability to adapt to changing circumstances and situations).
Because of Plato's attacks on the Sophists, Isocrates' school of rhetoric and philosophy came to be viewed as unethical and deceitful. Yet many of Plato's criticisms are hard to discern in the work of Isocrates, and at the end of his Phaedrus Plato even has Socrates praising Isocrates. Isocrates saw the ideal orator as someone who must not only possess rhetorical gifts, but possess also a wide knowledge of philosophy, science, and the arts. The orator should also represent Greek ideals of freedom, self-control, and virtue. In this, he was an influence on Roman rhetoricians, such as Cicero and Quintilian, and on the idea of liberal education.
On the art of rhetoric, he was also an innovator. He promoted a clear and natural style that avoided artificiality, while providing rhythm and variation that commanded the attention of the listener. Like most rhetoricians, he saw rhetoric as a method of clarifying the truth, rather than one of obscuring it.
Of the 60 orations in his name available in Roman times, 21 were transmitted by ancient and medieval scribes. Another three orations were found in a single codex during a 1988 excavation at Kellis, a site in the Dakhleh Oasis of Egypt. We have nine letters in his name, but the authenticity of four has been questioned. He is said to have compiled a treatise, the Art of Rhetoric, but it has not survived. In addition to the orations, other works include his autobiographical Antidosis and educational texts, such as Against the Sophists.