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 so far as they live at all, must, he sees, live by faith in what cannot be either proved or disproved by direct demonstration. And if all those final judgments of practical reason were contradicted in daily action, as well as in academic theory, 'piety, patriotism, parental affection, and private virtue would appear as ridiculous as knight-errantry: the pursuits of pleasure, ambition, and avarice must be grounded upon this sort of belief as well as those that are honourable and virtuous.'

On the other hand there are common prejudices which, while they last, are popularly dignified as 'common sense.' Some now universally admitted truths of science at first shocked men, although afterwards found to be in harmony with the general common sense to which philosophy appeals. That we are living on a material ball that revolves in space; that the revolving ball revolves also on its axis; that the sun does not rise and set, but is at rest; the existence of the antipodes; the invisibility of the distances of things—are a few examples. Instead of contradicting the common sense, the common sense, in the light of further experimental evidence, finally imposes them upon us. At any rate their contradictories cannot be justified by the universal intellectual paralysis which is the alternative to the rejection of a genuine judgment of the common sense. The assertion that the earth is in motion and the sun relatively at rest does not contradict sane human nature: that changes in nature are all wholly chaotic, and therefore wholly uninterpretable, can never become a scientific discovery, because it implies subversion of all science and makes scientific reasoning impossible. The invisibility of the distances of things, rightly understood in the light of its evidence, draws no protest from genuine human nature.