The Gorgias, written soon after the death of Socrates, represents the third and highest stage of this period. Directed against the Sophistical identification of pleasure and virtue, of the good and of the agreeable, _i. e._ against the affirmation of an absolute moral relativity, this dialogue maintains the proof that the good, far from owing its origin only to the right of the stronger, and thus to the arbitrariness of the subject, has in itself an independent reality and objective validity, and, consequently, alone is truly useful, and thus, therefore, the measure of pleasure must follow the higher measure of the good. In this direct and positive polemic against the Sophistic doctrine of pleasure, in its tendency to a view of the good as something firm and abiding, and secure against all subjective arbitrariness, consists prominently the advance which the Gorgias makes over the Protagoras.
In the first Socratic period the Platonic philosophizing became ripe and ready for the reception of Eleatic and Pythagorean categories. To grapple by means of these categories with the higher questions of philosophy, and so to free the Socratic philosophy from its so close connection with practical life, was the task of the second period.
THE SECOND PERIOD—the dialectic or the Megaric—is marked externally, by a less prominence of form and poetic contemplation, and not unfrequently indeed, by obscurity and difficulties of style, and internally, by the attempt to give a satisfactory mediation for the Eleatic doctrine and a dialectic foundation for the doctrine of ideas.
By his exile at Megara, and his journeys to Italy, Plato became acquainted with other and opposing philosophical directions, from which he must now separate himself in order to elevate the Socratic doctrine to its true significance. It was now that he first learned to know the philosophic theories of the earlier sages, for whose study the necessary means could not at that period, so wanting in literary publicity, be found at Athens. By his separation from these varying standpoints, as his older fellow pupils had already striven to do, he attempted striding over the narrow limits of ethical philosophizing, to reach the final ground of knowing, and to carry out the art of forming conceptions as brought forward by Socrates, to a science of conceptions, _i. e._ to the doctrine of ideas. That all human acting depends upon knowing, and that all thinking depends upon the conception, were results to which Plato might already have attained through the scientific generalization of the Socratic doctrine itself, but now to bring this Socratic wisdom within the circle of speculative thinking, to establish dialectically that the conception in its simple unity is that which abides in the change of phenomena, to disclose the fundamental principles of knowledge which had been evaded by Socrates, to grasp the scientific theories of the opposers direct in their scientific grounds, and follow them out in all their ramifications,—this is the problem which the Megaric family of dialogues attempts to solve.