158. Sense and Common Sense.
I have noticed two main evils in philosophizing. The first is the absurdity of demanding proof for the very facts which constitute the nature of him who demands it—a proof for those primary 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 Common Sense. 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.
As an instance of the latter evil, take that truly powerful and active intellect, Sir Thomas Brown, who, though he had written a huge volume in detection of vulgar errors, yet peremptorily pronounces the motion of the earth round the sun, and consequently the whole of the Copernican system, unworthy of any serious confutation, as being manifestly repugnant to Common Sense: which said Common Sense, like a milner's scales used to weigh gold or gasses, may and often does, become very gross, though unfortunately not very uncommon, nonsense. And as for the former (which may be called Logica Præpostera), I have read, in metaphysical essays of no small fame, arguments drawn ab extra in proof and disproof of personal identity, which, ingenious as they may be, were clearly anticipated by the little old woman's appeal to her little dog for the solution of the very same doubts, occasioned by her peticoats having been cut round about.
"If it is not me, he'll hark and he'll rail;
"But if I be I, he'll wag his little tail."