Joseph Heller, Catch-22

[Yossarian:] "Can't you ground someone who's crazy?"
[Doc Daneeka:] "Oh, sure. I have to. There's a rule saying I have to ground anyone who's crazy."
"Then why don't you ground me? I'm crazy. Ask Clevinger"
"Clevinger? Where is Clevinger? You find Clevinger and I'll ask him."
"Then ask any of the others. They'll tell you how crazy I am."
"They're crazy."
"Then why don't you ground them?"
"Why don't they ask me to ground them?"
"Because they're crazy, that's why."
"Of course they're crazy," Doc Daneeka replied. "I just told you they're crazy, didn't I? And you can't let crazy people decide whether you're crazy or not, can you?"
Yossarian looked at him soberly and tried another approach. "Is Orr crazy?"
"He sure is," Doc Daneeka said.
"Can you ground him?"
"I sure can. But first he has to ask me to. That's part of the rule."
"Then why doesn't he ask you to?"
"Because he's crazy," Doc Daneeka said. "He has to be crazy to keep flying combat missions after all the close calls he's had. Sure, I can ground Orr. But first he has to ask me to."
"That's all he has to do to be grounded?"
"That's all. Let him ask me."
"And then you can ground him?" Yossarian asked.
"No. Then I can't ground him."
"You mean there's a catch?"
"Sure there's a catch," Doc Daneeka replied. "Catch-22. Anyone who wants to get out of combat duty isn't really crazy."
There was only one catch and that was Catch-22, which specified that a concern for one's own safety in the face of dangers that were real and immediate was the process of a rational mind. Orr was crazy and could be grounded. All he had to do was ask; and as soon as he did, he would no longer be crazy and would have to fly more missions. Orr would be crazy to fly more missions and sane if he didn't, but if he was sane he had to fly them. If he flew them he was crazy and didn't have to; but if he didn't want to he was sane and had to. Yossarian was moved very deeply by the absolute simplicity of this clause of Catch-22 and let out a respectful whistle.
"That's some catch, that Catch-22," he observed.
"It's the best there is," Doc Daneeka agreed.

[Chapter V, "Chief White Halfoat"]

G.K. Chesterton, Orthodoxy

Every one who has had the misfortune to talk with people in the heart or on the edge of mental disorder, knows that their most sinister quality is a horrible clarity of detail; a connecting of one thing with another in a map more elaborate than a maze. 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.

[Chapter II, "The Maniac"]

G.K. Chesterton, Orthodoxy

Mysticism keeps men sane. As long as you have mystery you have health; when you destroy mystery you create morbidity. The ordinary man has always been sane because the ordinary man has always been a mystic. He has permitted the twilight. He has always had one foot in earth and the other in fairyland. He has always left himself free to doubt his gods; but (unlike the agnostic of to-day) free also to believe in them. He has always cared more for truth than for consistency. If he saw two truths that seemed to contradict each other, he would take the two truths and the contradiction along with them. His spiritual sight is stereoscopic, like his physical sight: he sees two different pictures at once and yet sees all the better for that.

[Chapter II, "The Maniac"]

G.K. Chesterton, Orthodoxy

There is a notion adrift everywhere that imagination, especially mystical imagination, is dangerous to a man’s mental balance. . . . Imagination does not breed insanity. Exactly what does breed insanity is reason. Poets do not go mad; but chess-players do. Mathematicians go mad, and cashiers; but creative artists very seldom. I am not, as will be seen, in any sense attacking logic; I only say that this danger does lie in logic, not in imagination. . . . The general fact is simple. Poetry is sane because it floats easily in an infinite sea; reason seeks to cross the infinite sea, and so make it finite. . . . The poet only asks to get his head into the heavens. It is the logician who seeks to get the heavens into his head. And it is his head that splits.

[Chapter II, "The Maniac]