BlackSwanとは 意味・読み方・使い方

語源

From 中期英語 blak swan, calqued from a Latin quotation from Satire VI (written late 1st century – early 2nd century B.C.E.) of the Roman poet Juvenal: “Rara avis in terris, nigroque simillima cygno [a bird as rare upon the earth as a black swan]!”. Equivalent to black +‎ swan.

Sense 2.1 (“something believed impossible or not to exist”) is from the fact that all swans were thought to have white plumage until black swans were discovered in Australia in the 17th century by Dutch explorers. Sense 2.2 (“rare and hard-to-predict event”) was popularized by the Lebanese-American author Nassim Nicholas Taleb (born 1960) in his book The Black Swan: The Impact of the Highly Improbable (2007): see the quotation.

発音

• (Received Pronunciation) IPA: /blæk ˈswɒn/
• (General American) IPA: /blæk ˈswɑn/
• 韻: -ɒn

名詞

black swan (plural black swans)

1. Cygnus atratus, a swan with black plumage and a red bill which is endemic to Australia. [from c. 1700]
   • 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 Investigation. […], volume I, London: John W[illiam] Parker, […], →OCLC, § 3, page 379:

     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 for three thousand years on the earth without meeting with them, may there not also be "men whose heads do grow beneath their shoulders," notwithstanding a rather less perfect unanimity of negative testimony from all observers? Most persons would answer No; it was more credible that a bird should vary in its colour, than that man should vary in the relative position of his principal organs.

   • 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, volumes 5 (1884–1886), Bloomington; Indianapolis, Ind.: Indiana University Press, published 1993, →ISBN, page 111:

     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.

   • 1961, Harold Jeffreys, “Estimation Problems”, in Theory of Probability (Oxford Classic Texts in the Physical Sciences), 3rd edition, Oxford, Oxfordshire: Clarendon Press, published 2003, →ISBN, paragraph 3.21, page 132:

     The original propounder of 'all swans are white' presumably based it on a sample of hundreds or thousands; but the verifications before the Australian black swan was discovered must have run into millions

   • 1999, G. D’Agostini, “Bayesian Reasoning versus Conventional Statistics in High Energy Physics”, in Wolfgang von der Linden, Volker Dose, Rainer Fischer, Roland Preuss, editors, Maximum Entropy and Bayesian Methods: Garching, Germany 1998: Proceedings of the 18th International Workshop on Maximum Entropy and Bayesian Methods of Statistical Analysis (Fundamental Theories of Physic; 105), Dordrecht, South Holland: Springer Science+Business Media, →DOI, →ISBN, footnote 19, page 166:

     This concept of "observation" is not like that of seeing a black swan, to mention a famous classical example. New particles leave signatures in the detector that on an event by event basis cannot be distinguished by other processes (background).

2. (figurative)
   1. Something believed impossible or not to exist, especially if an example is subsequently found; also, something extremely rare; a rara avis.

      (something extremely rare): Synonyms: rare bird, rarity, unicorn; see also Thesaurus:rarity

      • 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:

        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.

      • 1743, Henry Fielding, “Part of Juvenal’s Sixth Satire, Modernized in Burlesque Verse”, in Miscellanies, […], volume I, London: […] A[ndrew] Millar, […], →OCLC, page 97:

        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.

   2. (specifically, also attributive) A rare and hard-to-predict event with major consequences.
      • 2007, Nassim Nicholas Taleb, “Prologue”, in The Black Swan: The Impact of the Highly Improbable, New York, N.Y.: Random House, →ISBN, page xviii:

        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 dynamics.

      • 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 3 February 2023:

        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. How could anyone have predicted this? […] In the face of black swans – also known as fat-tail events, for the way their occurrences are distributed along a probability curve – market pricing may be impossible.

      • 2011 June 29, Azam Ahmed, “New investment strategy: Preparing for end times”, in The New York Times‎, New York, N.Y.: The New York Times Company, →ISSN, →OCLC, archived from the original on 23 December 2022:

        Worried that Greece could go belly up? So-called black swan funds – named for rare and unexpected events – offer a way to profit in the event of a market collapse.

上位語

• (Cygnus atratus): Anatidae – family; Anserinae – subfamily; Cygnus – genus

派生語

• black swan event
• black swan fallacy
• black swan theory

参考

• tail risk

参照

Further reading

• black swan on Wikipedia.Wikipedia
• black swan theory on Wikipedia.Wikipedia
• Category:Cygnus atratus on Wikimedia Commons.Wikimedia Commons
• Cygnus atratus on Wikispecies.Wikispecies