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in asserting, as a general principle, that “such and such a treatment cures the cholera”? Modern logic tells us that a statement of the kind requires verification; and modern writers, such as Bacon, Whewell, and Mill, are at great pains to point out the best methods of verification,—which after all consist in observing and experimenting further; in eliminating all accidental circumstances; in recording, and, if possible, accounting for, the facts which go against your principle; and, finally, in either rejecting it as unproven, or bringing it out as completely established after passing through the ordeal of thorough examination. But the minute and cautious methods of experiment and observation which have gradually come into use among scientific men in modern times were unknown in the days of Aristotle; so it is not to be wondered at that, having so much else to think of, he did not enter upon this field of inquiry. He tells us repeatedly that we must draw our general principles from familiarity with particular facts; but instead of suggesting methods of verification for the validity of those principles, he merely says that they must have the sanction of our reason. It seems to have been his idea that, after gathering facts up to a certain point, a flash of intuition would supervene, telling us, “This is a law.” Such, no doubt, has often been the case, as in Newton’s famous discovery of the law of gravitation from seeing an apple fall. Yet still, in the ordinary course of science, verification ought always to be at hand. And Aristotle, in omitting to provide for this, left a blank in his theory of the acquirement of knowledge.