(a) The polemics against the Sophists (written between his return from Egypt in 395 B. C. and his first Italian journey in 391 B. C.).
They are an attempt to present a solid front against the Sophists, and to show the weakness of the Sophistic doctrines. These polemical dialogues are:
Protagoras, a criticism of the Sophistic assumption that virtue is teachable, because that assumption is incompatible with the Sophistic fundamental principle;
Gorgias, showing how superficial the Sophistic rhetoric is when compared with true culture, which is the foundation of real statecraft;
Euthydemus, an exposition of the fallacies in the Sophistic eristic;
Cratylus, a criticism of the philological attempts of the Sophists;
Theætetus, a criticism of the Sophistic theories of knowledge;
The First Book of the Republic (the “Dialogue concerning Justice”), a criticism of the Sophistic naturalistic theory of the state.
(b) Meno, which contains the first positive statement by Plato of his own constructive theory. It is the first intimation of development beyond the simple Socratic theory of knowledge. Plato states this, however, rather timidly, by suggestions and after the manner of a mathematician.
3. Plato as Teacher of the Academy (387–347 B. C.). These forty years were spent by Plato in Athens as master and teacher of his school, the Academy, with the exception of two journeys to Italy. He undertook these journeys in the hope of realizing in a practical way his political ideals. He made his second Italian journey upon the invitation of Dion, in the hope of influencing the younger Dionysius, and the third Italian journey in order to reconcile Dion and Dionysius. This last journey brought him again into great personal danger.