The twin dialogues, "Gorgias" and "Theaetetus" are probably the earliest of this group. They result in nothing very definite, and are chiefly negative in character. Plato is here engaged merely in a preparatory clearing of the ground. The "Gorgias" discusses and refutes the Sophistic identification of virtue and pleasure, and attempts to show, as against it, that the good must be something objectively existent, and independent of the pleasure of the individual. The "Theaetetus," similarly, shows that truth is not, as the Sophists thought, merely the subjective impression of the individual, but is something objectively true in itself. The other {175} dialogues of the group are the "Sophist," the "Statesman," and the "Parmenides." The "Sophist" discusses Being and not-being, and their relationship to the theory of Ideas. The "Parmenides" inquires whether the absolute reality is to be regarded, in the manner of the Eleatics, as an abstract One. It gives us, therefore, Plato's conception of the relation of his own philosophy to Eleaticism. The dialogues of the third group are the work of Plato's maturity. He has now completely mastered his thought, and turns it with ease in all directions. Hence the style returns to the lucidity and purity of the first period. If the first period was marked chiefly by literary grace, the second by depth of thought, the third period combines both. The perfect substance is now moulded in the perfect form. But a peculiarity of all the dialogues of this period is that they take it for granted that the theory of Ideas is already established and familiar to the reader. They proceed to apply it to all departments of thought. The second period was concerned with the formulation and proof of the theory of Ideas, the third period undertakes its systematic application. Thus the "Symposium," which has for its subject the metaphysic of love, attempts to connect man's feeling for beauty with the intellectual knowledge of the Ideas. The "Philebus" applies the theory of Ideas to the sphere of ethics, the "Timaeus" to the sphere of physics, and the "Republic" to the sphere of politics. The "Phaedo" founds the doctrine of the immortality of the soul upon the theory of Ideas. The "Phaedrus" is probably to be grouped with the "Symposium." The beauty, grace, and lucidity of the style, and the fact that it assumes throughout that {176} the theory of Ideas is a thing established, lead us to the belief that it belongs to the period of Plato's maturity. Zeller's theory that it was written at the beginning of the second period, and is then offered to the reader as a sort of sweetmeat to induce him to enter upon the laborious task of reading the "Sophist," the "Statesman," and the "Parmenides," seems to be far-fetched and unnecessary. [Footnote 12] [Footnote 12: Zeller's _Plato and the Older Academy_, chap. iii.]