…If you argue with a madman, it is extremely probable that you will get the worst of it; for in many ways his mind moves all the quicker for not being delayed by the things that go with good judgment. He is not hampered by a sense of humour or by charity, or by the dumb certainties of experience. He is the more logical for losing certain sane affections. Indeed, the common phrase for insanity is in this respect a misleading one. The madman is not the man who has lost his reason. The madman is the man who has lost everything except his reason.
The madman’s explanation of a thing is always complete, and often in a purely rational sense satisfactory. Or, to speak more strictly, the insane explanation, if not conclusive, is at least unanswerable; this may be observed specially in the two or three commonest kinds of madness. If a man says (for instance) that men have a conspiracy against him, you cannot dispute it except by saying that all the men deny that they are conspirators; which is exactly what conspirators would do. His explanation covers the facts as much as yours. Or if a man says that he is the rightful King of England, it is no complete answer to say that the existing authorities call him mad; for if he were King of England that might be the wisest thing for the existing authorities to do. Or if a man says that he is Jesus Christ, it is no answer to tell him that the world denies his divinity; for the world denied Christ’s.
Nevertheless he is wrong. But if we attempt to trace his error in exact terms, we shall not find it quite so easy as we had supposed. Perhaps the nearest we can get to expressing it is to say this: that his mind moves in a perfect but narrow circle. A small circle is quite as infinite as a large circle; but, though it is quite as infinite, it is not so large. In the same way the insane explanation is quite as complete as the sane one, but it is not so large. A bullet is quite as round as the world, but it is not the world. There is such a thing as a narrow universality; there is such as thing as a small and cramped eternity; you may see it in many modern religions. Now, speaking quite externally and empirically, we may say that the strongest and most unmistakable mark of madness is this combination between a logical completeness and a spiritual contraction. The lunatic’s theory explains a large number of things, but it does not explain them in a large way. I mean that if you or I were dealing with a mind that was growing morbid, we should be chiefly concerned not so much to give it arguments as to give it air, to convince it that there was something cleaner and cooler outside the suffocation of a single argument. Suppose, for instance, it were the first case that I took as typical; suppose it were the case of a man who accused everybody of conspiring against him. If we could express our deepest feelings of protest and appeal against this obsession, I suppose we should say something like this: “Oh, I admit that you have your case and have it by heart, and that many things do fit into other things as you say. I admit that your explanation explains a great deal; but what a great deal it leaves out! Are there no other stories in the world except yours; and are all men busy with your business? Suppose we grant the details; perhaps when the man in the street did not seem to see you it was only his cunning; perhaps when the policeman asked you your name it was only because he knew it already. But how much happier you would be if you only knew that these people cared nothing about you! How much larger your life would be if your self could become smaller in it; if you could really look at other men with common curiosity and pleasure; if you could see them walking as they are in their sunny selfishness and their virile indifference! You would begin to be interested in them, because there were not interested in you. You would break out of this tiny and tawdry theater in which your own plot is always being played, and you would find yourself under a freer sky, in a street full of splendid strangers.” Or suppose it were the second case of madness, that of a man who claims the crown, your impulse would be to answer, “All right! Perhaps you know that you are the King of England; but why do you care? Make one magnificent effort and you will be a human being and look down on all the kings of the earth.” Or it might be the third case, of the madman who called himself Christ. If we said what we felt, we should say, “So you are the Creator and Redeemer of the world: but what a small world it must be! What a little heaven you must inhabit, with angels no bigger than butterflies! How sad it must be to be God; and an inadequate God! Is there really no life fuller and no love more marvelous than yours; and is it really in your small and painful pity that all flesh must put its faith? How much happier you would be, how much more of you there would be, if the hammer of a higher God could smash your small cosmos, scattering the stars like spangles, and leave you in the open, free like other men to look up as well as down!”
Full text: http://www2.hn.psu.edu/faculty/jmanis/gkchesterton/Orthodoxy.pdf