Yet the suicide, doubly slain in the Inquiry, may be used as a warning of the consequence of doing violence to the genuine common sense, or ideal man that is latent in each man; especially on subjects in which doubt is easier than in the case of outward things and persons. The 'metaphysical lunacy' of doubt about the existence of other persons may be acknowledged, while the common sense, unawake in its moral or spiritual elements, fails to protest against ethical atheism or agnosticism. What Reid calls the common sense is alive consciously in various degrees, in different persons, in different countries and periods. A common sense of the existence of outward things and persons is practically awake in all sane minds. But the spiritual convictions, of which some are hardly conscious, may be rejected even practically without obvious lunacy. And something is gained for those convictions, if it can be shown, as a reductio ad absurdum, that their rejection involves the moral sceptic too in the 'lunacy' of universal doubt and pessimist despair.
That Reid lays much stress on 'calling in question the common theory of ideas or images in perception' is explained by his assumption, that this theory involves perversion of the common sense even in its preliminary contact with outward things in sense, thus obviously discrediting it as the final court of appeal in every other instance. It may in this way be taken as a plea for a more faithful adherence on the part of philosophers to the genuine common-sense judgments, which can be made to respond to an adequate appeal, however dormant they may be in individuals. This final appeal to human nature must, in short, be to human nature as it is in fact, not to human nature as distorted in hypothesis.
