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 that they are but lies or shadows of the truth, they are stifled in the birth.

The question discussed is Knowledge; and the first definition of it proposed is "sensible perception." This Socrates connects with the old saying of Protagoras, "Man is the measure of all things;" and this he again links on to the still older doctrine of Heraclitus, "All things are becoming." "These ancient philosophers" (he says)—"the great Farmenides excepted—agreed that since we live in the midst of perpetual change and transition, our knowledge of all things must be relative. There is no such thing, they will tell you, as real existence. You should not say, 'this is white or black,' but, 'it is my (or your) impression that it is so.' And thus each man can only know what he perceives; and so far his judgment is true."

"Of course" (continues Socrates), "we might object that our senses may deceive us; that in cases where a man is mad or dreaming—who knows, indeed, whether we are not dreaming at this very moment—he must get false impressions: or, again, that our tastes may become perverted; and as wine is distasteful to a sick man, so what is really good or true does not appear so to us. But Protagoras would reply that the sick man's dreams are real to him,—that my impressions of wine are certainly different in health and sickness; but then I am different, and my impressions in either case are true."

"I wonder (says Socrates, ironically) that Protagoras did not begin his great work on Truth with a declaration that a