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306 and unceasing revelations of self-consciousness, which every possible proof must pre-suppose; reasoning, for instance, pro and con, concerning the existence of the power of reasoning. Other truths may be ascertained; but these are certainty itself, (all at least which we mean by the word) and are the measure of every thing else which we deem certain. The second evil is that of mistaking for such facts mere general prejudices, and those opinions that, having been habitually taken for granted, are dignified with the name of. Of these, the first is the more injurious to the reputation, the latter more detrimental to the progress of philosophy. In the affairs of common life we very properly appeal to common sense; but it is absurd to reject the results of the microscope from the negative testimony of the naked eye. Knives are sufficient for the table and the market,.. but for the purposes of science we must dissect with the lancet.