black swan

Noun

black swan (plural black swans)

1. Cygnus atratus, a swan with black plumage and a red bill which is endemic to Australia.
   • Mankind were wrong, it seems, in concluding that all swans were white: are we also wrong, when we conclude that all men's heads grow above their shoulders, and never below, in spite of the conflicting testimony of the naturalist Pliny? As there were black swans, though civilised people had existed...1843, John Stuart Mill, “Of the Ground of Induction”, in A System of Logic, Ratiocinative and Inductive, being a Connected View of the Principles of Evidence, and the Methods of Scientific...
   • If you tell me that there is or that there is not a black swan or a white raven, I want to know where you mean; and that you can only show me,—no description will answer the purpose.1884 summer, Charles Sanders Peirce, “On the Algebra of Logic (Second Paper) [Item 22, MS 508]”, in Christian J. W. Kloesel [et al.], editors, Writings of Charles S. Peirce: A Chronological Edition...
2. (figuratively) Something believed impossible or not to exist, especially if an example is subsequently found; also, something extremely rare; a rara avis.
   • I do but ſpeake in the perſon of Demetrius, & vnder Hippolita ſhadovv vvhat I intend to the rare, and neuer enough vvondred at Moſpa, the black ſvvan of beauty, & madg-hovvled of admiration.1605 (date written), Iohn Day [i.e., John Day], The Ile of Guls. […], London: […] [John Trundle], and are to bee sold by Iohn Hodgets […], published 1606, →OCLC, signature [D4], verso
   • A Virgin too, untouch'd, and chaſte, / VVhom Man ne'er took about the VVaiſte. / She's a rare Bird! find her vvho can, / And much reſembling a black Svvan.1743, Henry Fielding, “Part of Juvenal’s Sixth Satire, Modernized in Burlesque Verse”, in Miscellanies, […], volume I, London: […] A[ndrew] Millar, […], →OCLC, page 97

   Synonyms:

   rare bird, rarity, unicorn, hen's tooth, lightning in a bottle, one in a million, rara avis, rocking horse shit

3. (also, attributive, figuratively, specifically) A rare and hard-to-predict event with major consequences.
   • A small number of Black Swans explain almost everything in our world, from the success of ideas and religions, to the dynamics of historical events, to elements of our own personal lives. […] Fads, epidemics, fashion, ideas, the emergence of art genres and schools. All follow these Black Swan...2007, Nassim Nicholas Taleb, “Prologue”, in The Black Swan: The Impact of the Highly Improbable, New York, N.Y.: Random House, →ISBN, page xviii
   • The details of this catastrophe [the 2011 Fukushima nuclear accident] were unforeseeable, leading some to conclude this was a black swan event – something so wildly unexpected, so enormous in its impact, that it seems to defy our understanding and expose the fragility of our knowledge of the world....2011 March 19, Jeff Sommer, “A crisis that markets can’t grasp”, in The New York Times, New York, N.Y.: The New York Times Company, →ISSN, →OCLC, archived from the original on 03 Feb 2023