It is thus that Reid recognises his right in reason to grasp realities that are independent of his individual self; and he thinks that he is doing this philosophically by getting rid of the unphilosophical supposition, that he needs to work his way to them by logical reasoning, founded on wholly inward impressions. The true philosophy of perception with him is to discharge the medium, and at once take the bull by the horns. Some may think that the _Inquiry_ represents wasted labour—that the ‘metaphysical lunacy’ which abolishes personal pronouns as meaningless words, and inconsistently reasons that all who reason must be fools, is at the best the idle intellectual pastime of persons who pretend to be universal sceptics—all which Reid has taken too seriously, and which at any rate by its self-contradiction refutes itself. For it asserts that assertion is impossible. It is an argument that concludes for the rejection of the postulates without which it is impossible for human beings to reason at all. It is a philosophy that destroys itself in destroying all philosophy. The suicide does not need to be put to death. 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_.