Alice (with flamingo) chats with the Duchess
illustration by John Tenniel (1820-1914)
“Thinking again?” the Duchess asked, with another dig of her sharp little chin.
“I’ve a right to think,” said Alice sharply, for she was beginning to feel a little worried.
“Just about as much right,” said the Duchess, “as pigs have to fly.”
Alice’s Adventures in Wonderland (1865), by Lewis Carroll (Charles Lutwidge Dodgson – 1832-98)
This phrase is used to indicate incredulity or impossibility, or to mock credulity in others.
This notion is found in the obsolete proverb pigs fly with their tails forward, which redoubles the absurdity. It is first attested in Against Ierome Osorius Byshopp of Siluane in Portingall and against his slaunderous inuectiues An aunswere apologeticall: for the necessary defence of the euangelicall doctrine and veritie. First taken in hand by M. Walter Haddon, then undertaken and continued by M. Iohn Foxe, and now Englished by Iames Bell (1581), by Walter Haddon (1516-72), John Foxe (1516-87) and James Bell (floruit 1551-96):
You haue promised vs much more strong Argumētes and Reasons, brighter (as you say) then the Sunne it selfe on mydday: which you will so prynte out euen to the view and beholdyng of our most gracious Queéne: that at the twincklyng of an eye she shall be able easily to descry the vncleannesse, and wickednesse of this forged Religion: This is a great promise, my good Lord: But when will this be done? when pigges flye with their tayles foreward, and when S. Iames of Compostella, and our Lady of Waltsingham become man & wife.
Paroemiologia Anglo-Latina in usum scholarum concinnata. Or proverbs English, and Latine, methodically disposed according to the common-place heads, in Erasmus his adages. Very use-full and delightful for all sorts of men, on all occasions. More especially profitable for scholars for the attaining elegancie, sublimitie, and varietie of the best expressions (1639), by John Clarke (died 1658), also contains:
Pigs fly in the aire with their tailes forward.
Thomas Fuller (1654-1734) recorded the following in Gnomologia: Adagies and Proverbs; Wise Sentences and Witty Sayings, Ancient and Modern, Foreign and British (1732):
That is as likely as to see an Hog fly.
The earliest instance of the current form of the phrase, albeit in the singular, that I could find is in a letter written about betting on the St. Leger by “an admirer of British sports”, published in Bell’s Life in London, and Sporting Chronicle of Sunday 17th August 1834. The fact that the correspondent used quotation marks seems to indicate that it was an established idiom (he also wrote, in quotation marks, “HALF a loaf is better than NO bread”):
“a pig MIGHT fly, though it is, confessedly, a damn’d unlikely BIRD.”
In a letter published in The Liverpool Mercury of Tuesday 21st August 1849, a certain John Henry Goldsmith used, also in quotation marks, the same form, but in the plural:
“Pigs might fly, but they are very unlikely birds.”
The New Monthly Belle Assemblée of June 1840 published Mr. Pickwick’s Hat-Box, edited by Henry Ross, Esqu., which thus begins:
It has a very queer sound certainly. “How can any-one edit a hat-box?” asks my particularly cunning reader. “Pigs might ﬂy, but I’ll defy any-one to edit a hat-box?”
EQUIVALENT PHRASES IN SOME OTHER LANGUAGES
– French: quand les poules auront des dents (when hens have teeth)
– Italian: quando gli asini voleranno (when donkeys fly)
– Portuguese: nem que a vaca tussa (not even if the cow coughs)
– Spanish: cuando las ranas críen pelo (when frogs get hair), so ¡hasta que las ranas críen pelo! (until frogs get hair!), meaning if I never see you again it’ll be too soon!.