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SOC. Come then, on this assumption, let us question Protagoras or someone of those who agree with him. Man is the measure of all things, as your school says, Protagoras, of the white, the heavy, the light, everything of that sort without exception; for he possesses within himself the standard by which to judge them, and when his thoughts about them coincide with his sensations, he thinks what to him is true and really is. Is not that what they say?
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THEO. Yes.
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SOC. Does he, then, also, Protagoras, we shall say, possess within himself the standard by which to judge of the things which are yet to be, and do those things which he thinks will be actually come to pass for him who thought them? Take, for instance, heat; if some ordinary man thinks he is going to take a fever, that is to say, that this particular heat will be, and some other man, who is a physician, thinks the contrary, whose opinion shall we expect the future to prove right? Or perhaps the opinion of both, and the man will become, not hot or feverish to the physician, but to himself both?
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THEO. No, that would be ridiculous.
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SOC. But, I imagine, in regard to the sweetness or dryness which will be in a wine, the opinion of the husbandman, not that of the lyre-player, will be valid.
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THEO. Of course.
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SOC. And again, in a matter of discord or tunefulness in music that has never been played, a gymnastic teacher could not judge better than a musician what will, when performed, seem tuneful even to a gymnastic teacher himself.
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THEO. Certainly not.