It may perhaps be said that Reid makes his appeal to the root principles of practical reason—the essential sanity of mankind—only on behalf of what no one seriously calls in question; and moreover that he attributes the scepticism with which he struggled to a speculative theory of philosophers, instead of to facts in nature and in man, which suggest distrust in the ‘inspirations’ on which human understanding depends, in its lack of omniscience. What need, it may be asked, for a prolonged endeavour to justify belief in the existence of the house in which we live, the planet on which it stands, or the human beings among whom we seem to play our parts? Only insane persons—really insane—can be found to doubt realities like these. Insanity cannot be cured by an elaborate disproof of the ‘ideal system’; and as for the sane, such common sense sanities as these are safe enough without this philosophical appeal to human sanity. As regards those beliefs—_si non rogas intelligo_. I know all that I need to know, as long as I am not asked to justify and explain my knowledge, logically or otherwise, and remain contented to enjoy the things that unpractical thinkers vainly try to understand. That sceptical distrust in our original faculties, and in Power or Providence that is finally operative in the universe in which we have our being, lies deeper than the ‘ideal system’ which was Reid’s bugbear; and also that it arises mostly in connection with less obtrusive elements in the common sense than our perceptions through the five senses, is in harmony with the gradual development of Reid’s own thought which I have tried to trace. For he advanced, as we saw, from reflection upon those ‘inspirations’ of the common sense that are implied in our physical perceptions, to reflection upon those other data of the common sense that are implied in our perceptions of personal and morally responsible agency. It is in touching and seeing the material world that the common sense is first awakened; and thus the material world is the most obtrusive object in human experience, its perceptions affording the fittest preliminary object-lesson on the office of this final reason in the whole rational economy of man. External perceptions are the beginnings of all reasonings about concrete existence. They are the obvious examples of those original judgments, which are ‘the inspiration of the Almighty,’ more obvious than the often dormant ones that are moral and spiritual. All the discoveries of our reason are grounded on them. A remarkable deviation from them, arising from a disorder in the constitution, is called _lunacy_ by all; as when a man believes that he is made of glass: but when a man suffers himself to be reasoned out of them by metaphysical arguments he would call this _metaphysical lunacy_; which differs from the other species of the distemper in this, that it is not continued, but intermittent. He thus tests reason in its final