The Grammarphobia Blog

Let the cat out of the bag

Q: The expression “let the cat out of the bag” means to reveal a secret that’s impossible to take back. Why? This is a no-brainer for anyone who has ever tried to get a wise cat into a carrier to go to the veterinarian.  

A: It seems to be raining cats here. This is the second question we’ve had lately about feline expressions. The earlier posting discussed “the cat’s pajamas,” “the cat’s meow,” “the cat’s whiskers,” and similar phrases.

The Oxford English Dictionary agrees with you that “let the cat out of the bag” means to disclose a secret, but it doesn’t mention anything about the difficulty of taking the secret back.

The OED cites a 1760 quotation from the London Magazine: “We could have wished that the author … had not let the cat out of the bag.”

Eric Partridge’s A Dictionary of Slang and Unconventional English gives an earlier date, 1750, though it doesn’t provide a source.

But why a cat, and why a bag?

Brewer’s Dictionary of Phrase and Fable suggests this expression is a variation on the “pig in a poke” theme. Here’s Brewer’s explanation for the porcine phrase:

A pig in a poke. A blind bargain. The reference is to a common trick of yore of trying palm off on a greenhorn a cat for a sucking-pig. If he opened the poke or sack he ‘let the cat out of the bag,’ and the trick was disclosed. The ruse is referred to in Thomas Tusser’s Five Hundred Good Pointes of Husbandrie (1580). The French chat en poche refers to the fact, while our proverb refers to the trick.”

(We checked Tusser’s book and found a reference to “pig in a poke,” but nothing about letting cats out of bags.)

The American Heritage Dictionary of Idioms agrees with the Brewer’s explanation. It dates “let the cat out of the bag” from the mid-1700s and says:

“This expression alludes to the dishonest practice of a merchant substituting a worthless cat for a valuable pig, which is discovered only when the buyer gets home and opens the bag.”

We’re a little skeptical here. One would have to be a pretty dim bulb to mistake a cat—no doubt meowing and trying to claw its way out of the bag—for a squealing baby pig. And wouldn’t you look to see what you were getting for your money?

The word sleuth Michael Quinion doesn’t buy the pig story either. On his website World Wide Words, he says the expression “let the cat out of the bag” does indeed date back to the mid-18th century, but he adds:

“Anybody who has ever kept a live cat in a bag for more than a couple of seconds will know that even the most gullible purchaser would hardly mistake it for a piglet. It may just possibly be that the phrase comes from the explosive exit of a cat from a bag when it’s opened, so suggesting an original connection more with the shock and surprise of the event than of disclosure of the secret itself.”

Quinion concludes that there may be another explanation, now lost.

If somebody knows the secret, we’ll have to wait for him to let the cat out of the bag.

Check out our books about the English language