List of idioms of improbability

Look up when pigs fly in Wiktionary, the free dictionary.

There are many idioms of improbability, used to denote that something is impossible or unlikely to occur.

Flying pig (main article): A flying pig is a symbol of an impossible event coming to pass. The popular saying "[it will happen] when pigs fly" (or when pigs have wings) is traditionally used to mean that the specified event will never occur.
Cold hell: Rises from the general belief that hell is an extremely hot place. Expressions include "When hell freezes over", "A cold day in hell" and "A snowball's chance in hell."
If wishes were horses, beggars would ride (article)
Once in a blue moon (article)
Twelfth of Never (article on song title)

In other languages

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Albanian has the expression "ne 36 gusht" - (on August 36) to show something that is impossible to happen.
Arabic has a wide range of idioms differing from a region to another. In some Arab countries of the Persian Gulf people would say "إذا حجت البقرة على قرونها", which literally means "when the cow goes on pilgrimage on its horns" to express impossibility. In Egypt, they say "في المشمش", meaning "when the apricots bloom". Other Arab people -mainly Palestinian- use the expression "لما ينور الملح", which roughly translates into "when salt glows", which is futile because salt isn't a glowing material.
In Dutch, the expression is "met Sint-juttemis , or when Pentecost and Easter are on the same day: "Als Pinksteren en Pasen op één dag vallen" .
In Finnish, the expression is "sitten kun lehmät lentävät" - when the cows fly. Also "jos lehmällä olisi siivet, se lentäisi" (if cow had wings, it would fly), implying futile speculations. Also kun lipputanko kukkii (when flagpole blossoms) and Tuohikuussa Pukin-päivän aikaan - in Barkember on St. Buck's day (implying an imaginary month and imaginary day). Sometimes also kun Helvetti jäätyy ("when Hell freezes over"), although saying it alound to someone this is considered very rude and hostile.
In French, the expression is à la Saint-Glinglin (on Saint Glinglin's day). Glinglin is a nonsense rhyme for saint. Another expression is la semaine des quatres jeudis (the week of the four Thursdays) as in "that will happen (or not) during the week of the four Thursdays" (Thursday was the break in the school's week). Another expression is quand les poules auront des dents (when hens have teeth). The expression aux calendes grecques (to the Greek Calends) is also used for indefinite postponement, since calendes is a Roman feast.
In German "Wenn Schweine fliegen können!" is identical with the English saying "when pigs fly", although the older proverb "Wenn Schweine Flügel hätten, wäre alles möglich" (if pigs had wings, everything would be possible) is in more common use, often edited on the second part to something impossible, like "if pigs had wings, even your idea might work". Another phrase is "Am Sankt-Nimmerleins-Tag" (on St. Never's Day).
In Hebrew, a common idiom expressing improbability is "when hair grows on the palm of my hand" ("כשיצמחו שיערות על כף ידי"), a part of the human body where hair never grows. Another is a legal term, referring to the postponing of a case, "until Moses returns."
In Hungarian the two most often used expressions are "Majd ha piros hó esik" and "Majd ha cigánygyerekek potyognak az égből". The former is literally "When it's snowing red snowflakes", the latter: "When gypsy children are streaming from the sky". There is a third one: "Majd ha fagy" literally meaning "When it freezes". It's the short version of "Majd ha a pokol befagy", which literally means "When hell freezes over", but isn't used anymore.
Latin had the expression ad kalendas graecas (to the Greek Kalends) for indefinite postponement. The Greek calendar had no calends.
In Limburgish, the expression is "Te Pruimpaschen, als de kalveren op 't ijs dansen" (usually shortened to just "met Sint-juttemis"), meaning "on Saint-juttemis day, when the calves are dancing on the ice". This Saint-juttemis is usually thought to be a fictional saint in the vein of Saint Glinglin but is in fact real (St. Judith in English). Therefore Sint-juttemis day is an actual day (the 17th of August) and this makes saying just "on Saint-juttemis day" when you mean never a prime example of irony. The adding of the phrase "when the calves are dancing on the ice" is what makes the phrase impossible, because it never freezes on the 17th of August in the Netherlands.
In Lombard (Milanese dialect) the expression for something never occurring is "Quand pìssen i òch", which literally translates "When the geese will piss". The idiom refers to the popular belief that a goose never urinates.
In Malayalam, the expression is "കാക്ക മലർന്നു പറക്കും" (kākka malarnnu paṟakkuṃ), "[the] crow will fly upside down".^[1]
In Marathi, the expression is "आत्याबाईं ना मिश्या असत्या तर काका म्हंटले असते" meaning, "if aunt (here: father's sister) grows moustaches she would be called uncle" ^[2]
In Persian, the expression is "وقت گل نی" (vaght e gol e ney) - "when the reed plant blossoms".
In Polish, the expression is "na świętego nigdy" - "on Saint Never's Day".
In Portuguese, equivalent expressions are "no dia de São Nunca" ("on Saint Never's day") or "nem que a vaca tussa" (not even when the cow will cough)^[3]
In Russian, the expression is "когда рак на горе свистнет" (kogdá rak na goré svístnet) - "when the crawfish whistles on the mountain".
In Serbian, one expression is "кад на врби роди грожђе" (kad na vrbi rodi grožđe) - "when willow bears grapes". Another variant is "кад на врби засврби"(kad na vrbi zasvrbi) - "when willow get itchy". Note rhyme in vrbi zasvrbi. "Мало сутра" - (malo sutra) literally "a little bit tomorrow" has a similar meaning as "all my eye".
In Seychellois Creole, also known as Kreol or Seselwa (creole spoken in Seychelles) the expression "lannen de mil zanmen" is used, which means "year two thousand and never". It is a fairly new expression used mainly among the youth.
In Spanish, something that will never happen is often referred to as "cuando las vacas vuelen" ("when cows fly"). Its most common use is in response to an affirmative statement, for example "I saw Mrs. Smith exercising, I swear!" to which the response given would be something like, "Yeah right, and cows fly." Other variations slightly fallen into disuse include "cuando las ranas crien pelo" (when frogs grow hair) and "cuando San Juan agache el dedo" (when Saint John bends his finger). The latter one is a reference to the common depiction of St. John with one or two extended fingers.
In Tagalog, the vernacular is "kapag puti ng uwak, kapag itim ng tagak" - (when the crow turns white, when the egret turns black). Note the euphony between the nouns uwak and tagak.
In Turkish, one expression is "balık kavağa çıktığında" (when the fish climbs the poplar tree). Another one is "çıkmaz ayın son Çarşambasında" (at the last Wednesday of the endless month)

List of idioms of improbability

In other languages

See also

References