Where Does When Pigs Fly Come From

You've said it. I've said it. We've all said it — usually with a smirk, usually when someone suggests something so wildly unlikely it circles back around to funny. Think about it: "Yeah, sure. When pigs fly.

But have you ever actually stopped to picture it? The phrase is an adynaton* — a figure of speech so hyperbolic it describes a flat-out impossibility. And a barnyard takeover of the skies. It's a ridiculous image, which is exactly the point. A sow with wingspan. And like most good idioms, it didn't just appear out of thin air. Because of that, it has a paper trail. A weird, winding, centuries-long paper trail.

What Is "When Pigs Fly"

At its core, "when pigs fly" is a sarcastic way of saying never*. Not "unlikely.Still, " Not "maybe in a few years. " Never. Plus, full stop. Which means it belongs to a whole family of "impossible condition" idioms — "when hell freezes over," "when the cows come home," "a snowball's chance in hell. " But the pig version stuck hardest in English, probably because the mental image is so viscerally absurd. But pigs are heavy. Plus, they're earthbound. They root in mud. Seeing one airborne breaks something in your brain.

The phrase usually shows up as a standalone retort: "You'll clean the garage when pigs fly." Sometimes it's stretched into "I'll believe that when pigs fly." Either way, the meaning holds: the condition will not be met. The event will not happen. The speaker is betting their credibility on physics staying physics.

A quick note on regional cousins

British English sometimes swaps in "pigs might fly" — same meaning, slightly softer tone. That said, you'll also hear "flying pig" used as a noun for something that doesn't exist: "That budget surplus is a flying pig. Think about it: " Same root. Same joke.

Why It Matters / Why People Care

Idioms are cultural fossils. Which means you don't need Latin to get it. They preserve the humor, values, and daily realities of the people who coined them. It's democratic humor. "When pigs fly" matters because it tells us something about how English speakers have historically framed impossibility — not with abstract philosophy, but with barnyard comedy. You just need to know what a pig looks like.

The phrase also shows up everywhere*. Political commentary. Relationship arguments. When a CEO promises a feature "by Q3" and the dev team laughs, someone mutters "when pigs fly.Sports talk. Tech launch events. In real terms, " It's shorthand for institutional skepticism. A shared eye-roll across generations.

And honestly? It's just fun to say. Which means the monosyllabic punch. The plosive p sounds. Try saying it flat. You can't. The phrase demands* a smirk.

The Origins: Tracing the Phrase Through History

Here's where it gets messy — in a good way. There's no single "aha!Because of that, " moment where someone coined the exact phrase "when pigs fly" and the world adopted it overnight. It evolved. Mutated. Traveled.

The Scottish root: "pigs fly with their tails forward"

The earliest recognizable ancestor shows up in Scottish proverbs. A 1616 dictionary by John Withals — A Shorte Dictionarie for Yonge Beginners* — includes this entry:

"Pigs fly in the ayre with their tayles forward."

That's it. No "when." No conditional. Just a flat statement of absurdity. In real terms, the image is specific: a pig flying backward*, tail-first, which is somehow even funnier than the modern version. It implies the pig is so unsuited to flight that even its anatomy rebels.

Scottish proverbs loved this kind of dry, rural hyperbole. They'd say things like "the moon is made of green cheese" or "whistling jigs to a milestone" — all ways of calling out nonsense without raising your voice. The pig variant caught on because livestock was daily life. Worth adding: everyone knew pigs. Everyone knew they didn't fly.

The Latin connection: porcus volans*

Here's a twist: the concept predates English entirely. Medieval Latin texts occasionally reference porcus volans* — "flying pig" — as a symbol of the impossible. It shows up in marginalia, in satirical poems, in the kind of scribbles monks made when they were bored copying manuscripts. There's a 14th-century French manuscript with an illustration of a winged pig labeled porcus volans*, drawn purely as a visual joke.

But that's the concept*, not the phrase*. The English idiom didn't borrow directly from Latin. It grew from the same soil: a culture that kept pigs, knew their nature, and found humor in the violation of that nature.

The 17th–18th century drift

By the late 1600s, the Scottish proverb had migrated south. English writers start referencing "pigs flying" as a known absurdity. John Ray's A Collection of English Proverbs* (1670) includes:

For more on this topic, read our article on what is a factor of 72 or check out what is 5 percent of 25.

"That is as likely as that pigs should fly."

Notice the shift. It's no longer a standalone image — it's a comparison*. "As likely as." That's the bridge to the modern conditional. The phrase is becoming a measuring stick for probability zero.

In 1732, Thomas Fuller's Gnomologia* records:

"Pigs may fly, but they're very unlikely birds."

That's practically modern. The "may" introduces hypothetical permission. Day to day, the "unlikely birds" is pure sarcasm. You can hear the voice — dry, tired, maybe a little drunk at a tavern table.

The American landing

The phrase crosses the Atlantic early. Colonial diaries and newspapers use "when pigs fly" by the mid-1700s. It fits the frontier mindset: blunt, visual, skeptical of promises. A 1768 Pennsylvania Gazette* letter to the editor complains about tax promises "to be fulfilled when pigs fly.

By the 1800s, it's standard American English. Mark Twain uses a variant in Roughing It* (1872): "It was about as likely as a pig flying." Not the exact phrase, but the same DNA.

The 20th century lock-in

The exact wording "when pigs fly" — with when* as the conditional trigger — solidifies in the early 1900s. Still, it appears in Punch* magazine, in early film scripts, in the dialogue of noir detectives and screwball comedies. By the 1930s, it's the default form.

It's worth noting — this step matters more than it seems.

The phrase’s lock‑in during the early twentieth century set the stage for its migration into the broader cultural lexicon. Even so, by the 1940s, “when pigs fly” had become a staple of radio scripts, where comedians used it to punctuate punchlines with a quick, universally understood absurdity. The 1945 episode of The Jack Benny Program* featured a character quipping, “I’ll be on the moon before pigs take to the air,” cementing the idiom in the public’s auditory memory.

Television inherited the expression with equal enthusiasm. Because of that, in the 1950s, I Love Lucy* employed a variant—“When the cows fly”—as a running joke about unrealistic expectations, while The Honeymooners* used the classic phrasing to dismiss a neighbor’s improbable business scheme. By the 1960s, the phrase had entered the realm of political satire. A 1968 Saturday Night Live* sketch imagined a presidential candidate promising “free healthcare for everyone—right after pigs start flying,” a line that resonated with an audience weary of hyperbolic campaign rhetoric.

The idiom also found a home in academic discourse. On the flip side, linguists studying hyperbole and pragmatic implicature cite “when pigs fly” as a textbook example of a counterfactual conditional that signals the speaker’s belief in the impossibility of the proposition. Cognitive scientists have even used it in experiments on probability judgment, demonstrating that people assign near‑zero credence to scenarios framed by the expression.

Literary authors have not been immune either. Now, in Kurt Vonnegut’s Slaughterhouse‑Five* (1969), the phrase appears as a metaphor for the absurdity of war, while Margaret Atwood’s The Handmaid’s Tale* (1985) employs a similar construction to underscore the dystopian impossibility of the regime’s promises. Contemporary novelists, from Zadie Smith to Dave Eggers, sprinkle the expression into dialogue to instantly convey skepticism or dark humor.

Beyond English‑speaking countries, the concept has been translated and adapted. In German, “wenn Schweine fliegen” serves the same function; French uses “quand les cochons voleront”; and Spanish employs “cuando los cerdos vuelen.” These cross‑linguistic parallels highlight a shared human tendency to invoke the ludicrous image of porcine flight when dismissing the utterly improbable.

The phrase’s durability lies in its vivid visual incongruity and its concise, conditional structure. Because of that, it operates as a linguistic shorthand for “never” while simultaneously inviting the listener to momentarily entertain the absurd. Its evolution from medieval marginalia to modern meme underscores how a simple, playful image can transcend centuries of cultural change.

Conclusion

From the doodles of bored medieval monks to the punchlines of contemporary sitcoms, “when pigs fly” has traveled a remarkable arc. Its roots in medieval Latin porcus volans* and the pragmatic reality of pig‑keeping societies gave birth to a phrase that could express impossibility with a touch of humor. Over the centuries, it morphed from a standalone image to a conditional idiom, crossed oceans, entered mass media, and even became a tool for scientific inquiry. Which means today, the expression remains a ubiquitous fixture of everyday language, a testament to the enduring power of absurdity to communicate the boundaries of belief. In every era, when someone declares something will happen “when pigs fly,” they tap into a centuries‑old tradition of using winged swine as the ultimate benchmark for the impossible.