One of the most interessting books of the 20th century was the novel, Catch 22.

In the novel, the term "a catch 22 situation" was introduced.

The term has nothing to do with catching anything.

It has a much deeper meaning and it describes a kind of logical conundrum that's worth exploring.

First, it's important to put the phrase into context.

In the novel, a group of American bomber pilots is on an island in the Mediterranean.

They face death almost every day when they fly their bombing missions.

Many have already lost their lives.

The remaining pilots know that it is only a matter of time before they will be the next victims.

One of the characters in the novel is a doctor.

It is his job to see that the pilots are fit to fly.

In particular, there is a rule that says he has to ground anyone who is crazy.

To ground them means to remove them from active duty so that they don't fly.

Some of the men believed in the principles that they were fighting for.

They were willing to give their lives for their country.

But to other, this was crazy.

They thought the whole thing was insane.

One of them, Yossarian, wanted out.

He was friends with the doctor, and he wanted the doctor to ground him.

When Yossarian asked the doctor to ground him, the doctor replied: "You're wasting your time. You're not crazy."

Yossarian told him to asked one of the other pilots, Clevinger, to tell him how crazy he was.

"There's no point. He's crazy," the doctor replied. 

"Crazy people can't decide whether you're crazy or not."

"Clevinger isn't crazy! He's one of the sanest pilots here."

"So he's obviously out of his head,"said the Doc.

"He's got to be insane to keep on flying combat missions after all the close calls he's had."

"Well, if he's crazy, why don't you ground him?"

"I can't unless he asks to be grounded. That's part of the rule."

"So all he has to do is ask?"

"No, then I can't ground him."

"So there's a catch," said Yossarian, trying to get things straight.

"Sure, there's a catch," said the Doc, with a slight smile.

"Catch 22, if he asks then he can't be crazy. Only those who are crazy are grounded."

"That's some catch," observed Yossarian.

"It's the best there is," the Doc replied.