_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. What was the Academy? It was a public grove or garden in the suburbs of Athens (see map, p. 219) that had been left to the city for gymnastics by a public-spirited man named Academus. It had been surrounded by a wall and had been adorned by olive trees, statues, and temples. Near this inclosure Plato possessed by inheritance a small estate. It was here that he opened his school, and few places could be more favorable for the study of philosophy. Plato bequeathed this estate to the school, which held the property in a corporate capacity for several centuries. The leader of the school was called scholarch, and he appointed his own successor. The school was a kind of religious brotherhood based upon the worship of the Muses. Note that Democritus, Plato, and Aristotle finished their education at an age much beyond what is supposed to be the limit in modern time. They were, in fact, mature men before they began their life work. Plato was 32 before he began to teach in Athens and 40 before he set himself about his real life task in the founding of the Academy. Democritus was 40 before he returned to Abdera from his travels in Asia Minor. Aristotle was 41 when he undertook to act as tutor of Alexander, and 49 when he began his administration of the Lyceum. The dialogues of the third period of Plato’s life contain his constructive theory, and are his masterpieces of art. The topics with which they deal show the advance of his thought over the dialogues of his first period. The purely Socratic dialogues were ethical discussions; these are ethical, metaphysical, and physical. _Phædrus_, Plato’s delivery of his programme upon his entrance into active teaching in the Academy, in 386 B. C.