let the cat out of the bag

The popular story

Two explanations circulate for let the cat out of the bag, and both are told with great confidence. The first ties the phrase to a supposed market swindle. A trader, the story goes, would sell a suckling pig, hand over a tied sack, and hope the buyer did not open it until safely home — because inside was not a piglet but a worthless cat. To open the sack early was to let the cat out of the bag and expose the fraud. This tale is usually paired with its cousin, buying a pig in a poke, a poke being an old word for a small bag.

The second story is nautical. The cat, on this reading, is the cat o’ nine tails, the knotted whip used to flog sailors. The lash was kept in a bag, and drawing it out signalled that punishment was coming. To let this cat out of the bag was to reveal an unwelcome truth. Both versions are vivid, memorable, and repeated in countless etymology books.

What the record shows

The phrase itself can be dated with reasonable confidence. Its earliest known appearance in print is a review in The London Magazine in 1760, where a critic complained of an author:

We could have wished that the author… had not let the cat out of the bag.

Here the meaning is already the modern one: the author has given away too much, spoiling something by disclosure. There is no reference to markets, pigs, or whips — only to a secret carelessly revealed.

The trouble begins when we look for evidence tying that 1760 sense to either backstory. The market-fraud explanation is plausible on its face, and phrases about cheats and pokes are genuinely old: warnings against buying a pig in a poke are recorded from the sixteenth century. Similar livestock-swindle expressions exist in Dutch and German. But no writer of the period actually connects the swindle to the cat-and-bag phrase, and there is a practical objection: a cat and a piglet feel and sound nothing alike, and a buyer would notice the difference long before reaching home. The link is asserted, never demonstrated.

The cat o’ nine tails theory fares worse. The whip is well documented, but the naval sense does not match the phrase’s earliest recorded meaning, which is about disclosing information, not delivering a beating. Etymologists such as Gary Martin treat this explanation as dubious at best.

It is worth pausing on why the market-fraud story is so persistent. It has the shape of a satisfying etymology: a concrete scene, a clever swindle, and a neat pairing with ‘pig in a poke’, which really is an old and genuine expression. Once two phrases sound as though they belong together, the mind supplies a shared history whether or not one exists. Etymology is full of these tidy couplings, and they are precisely the cases where a careful reader should ask for a citation rather than a picture. In this instance the citation never comes: dictionaries repeat the market story, but none can point to a period source that ties the swindle to the words.

The verdict

The most honest verdict is unproven. We can say when the phrase surfaces — by 1760 — and what it meant, but we cannot say why. Both popular origins are stories retrofitted to a phrase whose real birth went unrecorded. Neither is impossible; neither is supported. A confident claim that the idiom ‘comes from’ cat-selling frauds goes beyond the evidence.

What we don’t know

We do not know who first used the expression, in what setting, or what mental image lay behind it. The 1760 citation is a first sighting, not a first use — the phrase reads as though it was already familiar to readers, which suggests it circulated in speech beforehand. How long beforehand, and in what form, is simply lost. Occasional claims of much earlier use, including a supposed sixteenth-century German letter, refer to the separate pig in a poke idea, not to this phrase.

How it changed

What is striking is how stable the phrase has been. From its first appearance it has meant, more or less, what it means now: to reveal something that should have been kept quiet. Unlike many idioms, it has not drifted in sense or shed a literal meaning over time. The image — a live thing escaping a bag, impossible to put back — carries the idea of an irreversible disclosure, and that instinctive picture has kept the phrase intact for over two and a half centuries.

If anything has shifted, it is the tone. The 1760 reviewer used the phrase drily, as an established figure of speech; over time it has become one of the most casual idioms in English, reached for in gossip, journalism, and advertising alike. Its survival owes something to that self-contained image. A phrase you can picture — a cat springing free of a sack — needs no explanation to work, which is why it has weathered the loss of whatever original scene, if any, first inspired it.

Usage today

Today the idiom is thoroughly everyday, used for everything from spoiled surprises to leaked corporate news. It carries a faint sense of accident or indiscretion: one usually lets the cat out of the bag rather than deliberately releasing it, and the phrase implies the secret cannot now be recovered. When you use it, you are reaching for a picture that has outlived its own explanation — which is a fitting fate for a phrase whose origin remains, honestly, unknown.

For a site built on accuracy, this one is a useful cautionary tale. The temptation is always to hand the reader a story, because a story feels like an answer. But the responsible account of let the cat out of the bag is shorter and less colourful than the market-swindle version: we know when it appears, we know what it means, and we do not know why. Saying so plainly is not a failure of research; it is the result of it.