A paradox in which the attempt to escape makes escape impossible.
The title of Joseph Heller's novel, written in 1953 and published in 1961, (properly titled 'Catch-22' - with a hyphen). The first chapter was also published in a magazine in 1955, under the title 'Catch-18'.
The paradox is presented as the trap that confined members of the US Air Force. In logical terms the 'catch' was that, by applying for exemption from highly dangerous bombing missions on the grounds of insanity, the applicant proved himself to be sane (after all, that's what any sane person would do). If anyone applied to fly they would be considered insane. Either way; sane or insane, they were sent on the missions. This might be described logically as, 'damned if you do and damned if you don't', 'the vicious circle', 'a chicken and egg situation', or 'heads I win, tails you lose'.
In the book, this is explained thus:
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 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.
The phrase is now often misapplied to any problematic or unwelcome situation.
See other phrases that were coined in the USA.