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Who really said it

Extraordinary claims require extraordinary evidence

Written by Carl Sagan 1934–1996 · American astronomer, planetary scientist & science communicator
Verified In copyright

Genuine, and locatable to the page. Sagan wrote it in Broca’s Brain: Reflections on the Romance of Science (Random House, 1979), in the chapter “Night Walkers and Mystery Mongers” — Wikiquote’s sourced entry ↗ gives the fuller sentence as “I believe that the extraordinary should certainly be pursued. But extraordinary claims require extraordinary evidence.” He also said the line on camera in Cosmos. One honest caveat: the sentence is his, but the thought is not new to him — Quote Investigator ↗ traces the family of sayings back to 1708, and Marcello Truzzi published “Extraordinary claims require extraordinary proof” in 1975.

Last verified 10 Aug 2026 · how we verify · spot an error?

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Verified quote & credit

“Extraordinary claims require extraordinary evidence” Carl Sagan, Broca's Brain: Reflections on the Romance of Science (New York: Random House, 1979), chap. 5, "Night Walkers and Mystery Mongers" — "I believe that the extraordinary should certainly be pursued. But extraordinary claims require extraordinary evidence." Sagan also spoke the line in Cosmos: A Personal Voyage, episode 12 (1980). The wording is genuinely his, but Marcello Truzzi had published "Extraordinary claims require extraordinary proof" in 1975, and Quote Investigator traces the family of sayings to 1708. Verified via Quotle.info.

Can you use it?

Still under copyright (rights held by The Estate of Carl Sagan and Random House (Penguin Random House)). A short, credited quote is generally fine for talks, teaching, and internal decks; for commercial, published, or large-scale reuse, get permission.

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In context

Evoking the world of Carl Sagan — American astronomer, planetary scientist & science communicator. Theme: "Extraordinary claims require extraordinary evidence". Atmospheric and restrained, cinematic directional light, a muted period-appropriate palette, fine grain and texture. Compose with generous empty space for the quote and a small credit line. No lettering in the image itself.

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Provenance

Where the line actually appears

Work
Broca’s Brain: Reflections on the Romance of Science
Chapter
Chapter 5, “Night Walkers and Mystery Mongers”
First published
Random House, New York, 1979
Also spoken
Cosmos: A Personal Voyage, episode 12, “Encyclopaedia Galactica” (1980)

I believe that the extraordinary should certainly be pursued. But extraordinary claims require extraordinary evidence. Broca’s Brain, 1979

Two reliable sources cite two different pages, because they used two different printings: Quote Investigator ↗ gives quote page 62 of the 1979 Random House edition, while Wikiquote ↗ gives p. 73 and states that its page numbers come from the October 1980 Ballantine Books mass-market paperback. The chapter is the same in both.

Scanned book, lending library
Borrow Broca’s Brain at the Internet Archive
Quote Investigator’s full chronology, 1708 to 2012

How we traced it

  • Started with the specialists. Quote Investigator ↗ has investigated this saying in depth, listing twenty dated instances. Its verdict is that the saying is centuries old and that “in modern times, it was popularized by Marcello Truzzi and Carl Sagan” — not coined by either.
  • Pinned Sagan’s own wording to a book. Wikiquote’s sourced section ↗ places it in Broca’s Brain (1979), chapter 5, with the preceding sentence intact; Quote Investigator cites the same book and chapter independently.
  • Checked the earlier Sagan use. Quote Investigator documents the wording in Sagan’s mouth two years before the book: The Washington Post, 16 December 1977, Weekend section, Art Harris’s piece “Second View: Sagan on ‘Encounters’”, page 1. That is the earliest Sagan instance Quote Investigator records.
  • Confirmed the broadcast. Wikipedia ↗ records that in Cosmos episode 12, “Encyclopaedia Galactica”, Sagan states the line while discussing claims that extraterrestrials have visited Earth.
In copyright

Broca’s Brain was first published by Random House in 1979 — well after the 1931 United States public-domain cutoff — so the text remains in copyright, and so does the 1980 Cosmos broadcast. Quoting the single sentence for commentary and attribution is ordinary fair use; reproducing the chapter is not.

Rights status is our research, not legal advice — and copyright varies by country and edition. For commercial or published use, confirm with the rightsholder. See terms.

Fact-check

What people get wrong

This one is unusual for a famous-name quote: the attribution is right. Sagan really wrote these five words. What gets misattributed is the invention — calling it the “Sagan standard” has quietly credited him with a principle that several other people had already written down, in almost these words.

Carl Sagan Popularizer, not originator

Sagan is routinely described as having coined the maxim. He did not. Quote Investigator ↗ concludes that the saying “has been in circulation for at least a few hundred years” and that “in modern times, it was popularized by Marcello Truzzi and Carl Sagan” — its earliest listed instance is Benjamin Bayly in 1708.

Marcello Truzzi “Proof,” not “evidence”

Truzzi is often given as the true author of this exact sentence. He is not — he wrote a different noun. Quote Investigator cites a letter from Truzzi in Parapsychology Review, November–December 1975: “Extraordinary claims require extraordinary proof.” Wikipedia ↗ cites his 1978 Zetetic Scholar article “On the Extraordinary: An Attempt at Clarification” for “An extraordinary claim requires extraordinary proof.” The swap to “evidence” is Sagan’s.

Pierre-Simon Laplace A translation, not a quotation

Laplace is frequently posted as the original author of this English sentence. He wrote in French, and about a century and a half earlier. Quote Investigator renders his 1810 formulation as “the more extraordinary a fact, the more it needs to be supported by strong proofs”; Wikipedia ↗ gives it as “the weight of evidence for an extraordinary claim must be proportioned to its strangeness.” Neither is the sentence people attach his name to.

So: the words are Sagan’s, published in Broca’s Brain ↗ in 1979 and spoken on Cosmos in 1980 — but he was joining an argument that, on Quote Investigator’s evidence, had been running since at least 1708.

Context

Why he said it

Sagan was not making an abstract point about epistemology. He was talking about flying saucers. Broca’s Brain collects essays he published through the 1970s, and the chapter this line sits in — “Night Walkers and Mystery Mongers” — is a working scientist’s patience finally running out with astrology, psychic surgery and alien abduction. The sentence before it is the part people forget: he says the extraordinary should be pursued. The standard is a gate, not a wall.

The same argument reached a vastly larger audience the following year. In Cosmos episode 12, “Encyclopaedia Galactica” ↗, Sagan spends the hour on the genuine search for extraterrestrial intelligence — and uses this line to separate that search from claims that extraterrestrials have been landing in fields. Wikipedia notes the phrase is now often shortened to ECREE and called the Sagan standard.

I believe that the extraordinary should certainly be pursued. But extraordinary claims require extraordinary evidence.

Three centuries of near-misses

Quote Investigator’s chronology ↗ shows how long people had been circling this sentence before Sagan landed it. Benjamin Bayly in 1708: “these Matters being very extraordinary, will require a very extraordinary Proof.” Elihu Palmer in 1804: “I ought to have extraordinary evidence, to induce me to believe extraordinary things.” William Craig Brownlee in 1824: “Extraordinary claims can rest only on extraordinary proofs.” Ely Vaughan Zollars in 1895: “Extraordinary claims always call for extraordinary proof.”

The philosophical ancestor most often named is David Hume’s 1748 essay “Of Miracles” ↗, Section X of the Enquiry Concerning Human Understanding, where the test for believing a reported miracle is whether “the falsehood of his testimony would be more miraculous, than the event which he relates.” Quote Investigator also records Hume’s shorter formulation from the same year: “A wise Man, therefore, proportions his Belief to the Evidence.”

Explore

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More provenance-checked quotes on the same theme, each with its reuse status.

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Trusted places to keep pulling the thread — primary archives, fact-checks, and scholarship. We show how we used each one before you leave.

Quote Investigator: Extraordinary Claims Require Extraordinary Evidencequoteinvestigator.com

The definitive chronology: twenty dated attestations from Benjamin Bayly in 1708 through Truzzi in 1975 to Sagan in 1977 and 1979, each with a full bibliographic citation.
Wikiquote: Carl Saganen.wikiquote.org

The sourced Broca's Brain (1979) section, giving the line in its full two-sentence context with a chapter and page citation to the Ballantine paperback.
Wikipedia: Extraordinary claims require extraordinary evidenceen.wikipedia.org

The aphorism's own encyclopedia entry — the "Sagan standard" and ECREE naming, the Cosmos episode 12 usage, and the Hume and Laplace precedents.
Broca's Brain (full scan, borrowable)archive.org

A scanned copy of Broca's Brain in the Internet Archive lending library, so you can read the chapter rather than trust a quote card.
Wikipedia: Marcello Truzzien.wikipedia.org

The sociologist who published the near-identical "proof" formulation before Sagan, with the Zetetic Scholar 1978 citation.
Wikipedia: Of Miracles (Hume, 1748)en.wikipedia.org

The 18th-century philosophical ancestor everyone reaches for — Hume's testimony-versus-miracle test, in his own words.

The author

Who was Carl Sagan?

Carl Sagan

1934–1996 · American astronomer, planetary scientist & science communicator

Carl Sagan (9 November 1934 – 20 December 1996) was an American astronomer and planetary scientist who held the David Duncan Professorship of Astronomy and Space Sciences at Cornell University, where he directed the Laboratory for Planetary Studies. He won the 1978 Pulitzer Prize for General Nonfiction for The Dragons of Eden, and in 1980 co-wrote and narrated the thirteen-part PBS series Cosmos: A Personal Voyage, which reached an audience Wikipedia puts at at least 500 million viewers in 60 countries. His 1979 essay collection Broca’s Brain gathered a decade of magazine pieces, several of them sustained attacks on pseudoscience — which is exactly where this sentence lives.

For writers & researchers

Cite this

Cite this

Carl Sagan, Broca’s Brain: Reflections on the Romance of Science (New York: Random House, 1979), chap. 5, “Night Walkers and Mystery Mongers”: “But extraordinary claims require extraordinary evidence.” Quote Investigator locates the line at p. 62 of the Random House edition; Wikiquote cites p. 73 of the October 1980 Ballantine Books paperback. Sagan also spoke the line in Cosmos: A Personal Voyage, episode 12, “Encyclopaedia Galactica” (1980).

This verification page

Quotle.info. “Who really said ‘Extraordinary claims require extraordinary evidence’?” Last verified 10 Aug 2026. https://quotle.info/who-said/extraordinary-claims-require-extraordinary-evidence/

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