Sagan standard

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Carl Sagan in 1987

The Sagan standard is a neologism abbreviating the aphorism that "extraordinary claims require extraordinary evidence" (ECREE).[1] It is named after science communicator Carl Sagan who used the exact phrase on his television program Cosmos.

Similar statements were previously made by figures such as Théodore Flournoy in 1899, Pierre-Simon Laplace in 1814, and Thomas Jefferson in 1808.


The Sagan standard, according to Tressoldi (2011), "is at the heart of the scientific method, and a model for critical thinking, rational thought and skepticism everywhere".[2]

ECREE is related to Occam's razor in the sense that according to such a heuristic, simpler explanations are preferred to more complicated ones. Only in situations where extraordinary evidence exists would an extraordinary claim be the simplest explanation.[3] A routinized form of this appears in hypothesis testing where the hypothesis that there is no evidence for the proposed phenomenon, what is known as the "null hypothesis", is preferred. The formal argument involves assigning a stronger Bayesian prior to the acceptance of the null hypothesis as opposed to its rejection.[4]

There are no concrete parameters as to what constitutes "extraordinary claims", which raises the issue of whether the standard is subjective. According to Tressoldi this problem is less apparent in clinical medicine and psychology where statistical results can establish the strength of evidence.[2]


The aphorism was made popular by astronomer Carl Sagan who used it in the 1980 television show Cosmos in reference to claims about aliens visiting Earth.[5] Two 1978 articles, one in U.S. News & World Report and another by Koneru Ramakrishna Rao in the Journal of Parapsychology both quote physicist Philip Abelson, then the editor of Science, using the same phrase.[6][7] In "On the Extraordinary: An Attempt at Clarification" (1978), sociologist Marcello Truzzi said "an extraordinary claim requires extraordinary proof."[8]

Others have put forward very similar ideas. Psychologist Théodore Flournoy, in 1899, put forward the principle that "the weight of evidence for an extraordinary claim must be proportioned to its strangeness",[9] attributing the idea to Laplace, whom he quotes saying, in 1814, that "we ought to examine [seemingly inexplicable phenomena] with an attention all the more scrupulous as it appears more difficult to admit them".[10] Also in 1808, Thomas Jefferson said "A thousand phenomena present themselves daily which we cannot explain, but where facts are suggested, bearing no analogy with the laws of nature as yet known to us, their verity needs proofs proportioned to their difficulty."[11]

In popular culture[edit]

In 2004 the cyclist Lance Armstrong used the phrase "Extraordinary allegations require extraordinary evidence" to discredit allegations of doping put to him by journalist David Walsh.[12][13] Armstrong was later asked "What is it about you that makes ordinary proof insufficient to bring you down? For murderers, we're not looking for extraordinary proof, we're looking for proof. But you're saying it must be extraordinary. Why?".[14] Armstrong later confessed to doping in 2013.[15]

See also[edit]


  1. ^ Kaufman, Marc (2012). First Contact: Scientific Breakthroughs in the Hunt for Life Beyond Earth (Reprint ed.). Simon and Schuster. p. 124. ISBN 978-1439109014.
  2. ^ a b Tressoldi, Patrizio E. (2011). "Extraordinary Claims Require Extraordinary Evidence: The Case of Non-Local Perception, a Classical and Bayesian Review of Evidences". Frontiers in Psychology. 2 (117): 117. doi:10.3389/fpsyg.2011.00117. PMC 3114207. PMID 21713069.
  3. ^ Smith, Jonathan C. (2011). Pseudoscience and Extraordinary Claims of the Paranormal: A Critical Thinker's Toolkit. John Wiley & Sons. ISBN 978-1444358940.
  4. ^ Matthews, Paul (2010). Sample Size Calculations: Practical Methods for Engineers and Scientists. Mathews Malnar and Bailey. p. 6. ISBN 978-0615324616.
  5. ^ Sagan, Carl (December 14, 1980). "Encyclopaedia Galactica". Cosmos: A Personal Voyage. Episode 12. 01:24 minutes in. PBS.
  6. ^ "A Stepchild of Science Starts to Win Friends". U.S. News & World Report. July 31, 1978. pp. 41–42. Archived from the original on October 15, 2017. Retrieved October 14, 2017. Philip H. Abelson, editor of the authoritative journal Science, agrees that parapsychological research has improved markedly, but he is dubious about the results. "These extraordinary claims require extraordinary evidence," he contends.
  7. ^ Rao, K.R., 1978, Psi: Its place in nature. Journal of Parapsychology vol 42.
  8. ^ Marcello Truzzi, "On the Extraordinary: An Attempt at Clarification Archived April 11, 2019, at the Wayback Machine", Zetetic Scholar, Vol. 1, No. 1, p. 11, 1978.
  9. ^ Flournoy, Théodore (1899). Des Indes à la planète Mars: étude sur un cas de somnambulisme avec glossolalie. Slatkine. pp. 344–345. ISBN 9782051004992. Archived from the original on January 20, 2021. Retrieved December 4, 2020.*Flournoy, Théodore (2007). From India to the Planet Mars: A Study of a Case of Somnambulism. Daniel D. Vermilye, trans. Cosimo, Inc. pp. 369–370. ISBN 9781602063570. Archived from the original on January 20, 2021. Retrieved December 4, 2020.
  10. ^ Laplace, Pierre-Simon de (1825). Essai philosophique sur les Probabilités (in French) (5th ed.). pp. 134–135. Archived from the original on July 6, 2019. Retrieved July 6, 2019.
  11. ^ Berkes, Anna (November 14, 2008). "Who is the liar now?". Thomas Jefferson Foundation. Archived from the original on October 30, 2016. Retrieved October 29, 2016. Letter to Daniel Salmon on 15 February 1808 discussing the nature and origin of meteorites. U.S. Library of Congress image Archived 2017-08-22 at the Wayback Machine
  12. ^ Fotheringham, William (August 24, 2012). "Lance Armstrong shying away from a fight is an extraordinary moment - William Fotheringham". Archived from the original on November 7, 2018. Retrieved November 6, 2018 – via
  13. ^ Gittings, Paul (July 1, 2013). "The man who exposed Lance Armstrong's doping lies". CNN. Archived from the original on September 23, 2017. Retrieved January 20, 2021.
  14. ^ Chappell, Matt. "The State Of Doping In Sport In 2015, By David Walsh". AskMen. Archived from the original on 2019-01-19. Retrieved January 18, 2019.
  15. ^ Carter, Chelsea J. "Lance Armstrong facing lifetime ban, loss of titles". CNN. Archived from the original on January 19, 2019. Retrieved January 18, 2019.