5. INDIVIDUAL SOPHISTS.—The first, who is said to have been called, in the received sense, Sophist, is _Protagoras_ of Abdera, who flourished about 440 B. C. He taught, and for wages, in Sicily and in Athens, but was driven out of the latter place as a reviler of the gods, and his book concerning the gods was burnt by the herald in the public market-place. It began with these words: “I can know nothing concerning the gods, whether they exist or not; for we are prevented from gaining such knowledge not only by the obscurity of the thing itself, but by the shortness of the human life,” In another writing he develops his doctrine concerning knowing or not-knowing. Starting from the Heraclitic position that every thing is in a constant flow, and applying this preëminently to the thinking subject, he taught that the man is the measure of all things, who determines in respect of being that it may be, and of not-being that it may not be, _i. e._ that is true for the perceiving subject which he, in the constant movement of things and of himself, at every moment perceives and is sensible of—and hence he has theoretically no other relation to the external world than the sensuous apprehension, and practically no other than the sensuous desire. But now, since perception and sensation are as diverse as the subjects themselves, and are in the highest degree variable in the very same subject, there follows the farther result that nothing has an objective validity and determination, that contradictory affirmations in reference to the same object must be received as alike true, and that error and contradiction cannot be. Protagoras does not seem to have made any efforts to give these frivolous propositions a practical and logical application. According to the testimony of the ancients, a personal character worthy of esteem, cannot be denied him; and even Plato, in the dialogue which bears his name, goes no farther than to object to his complete obscurity respecting the nature of morality, while, in his Gorgias and Philebus, he charges the later Sophists with affirming the principles of immorality and moral baseness.