Extraordinary Claims Require Extraordinary Evidence

Carl Sagan? Marcello Truzzi? Pierre-Simon Laplace? David Hume? Benjamin Bayly? Elihu Palmer? William Craig Brownlee? F. B. Barton? William Denton? Ely Vaughan Zollars? Joseph Rinn? James Oberg? Arthur C. Clarke?

Dear Quote Investigator: Tabloid newspapers have printed remarkable claims about alien abductions, mischievous ghosts, bigfoot sightings, and other anomalies. Skeptics have countered these reports by stating that the evidence is inadequate. Here are two versions of a pertinent adage:

Extraordinary claims require extraordinary evidence.
Extraordinary claims require extraordinary proof.

This saying has been attributed to astronomer Carl Sagan, sociologist Marcello Truzzi, and mathematician Pierre-Simon Laplace. Would you please explore this topic?

Quote Investigator: These sayings form a natural family although the vocabulary and phrasing varies. The following overview with dates shows the evolution:

1708: These matters being very extraordinary, will require a very extraordinary proof (Benjamin Bayly)

1738: As it is a matter of an extraordinary kind, it is but reasonable in us to require extraordinary evidence for it

1740: Every man has a right to demand extraordinary evidence for any extraordinary fact (Arthur Ashley Sykes)

1741: Assertions so contrary to fact … require some extraordinary proof to gain our credit and assent (John Straight)

1748: A wise man, therefore, proportions his belief to the evidence (David Hume)

1748: No testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavours to establish (David Hume)

1800: Miracles being very unusual and extraordinary facts, they require very strong evidence to support them (Beilby Porteus)

1804: I ought to have extraordinary evidence, to induce me to believe extraordinary things (Elihu Palmer)

1810: Plus un fait est extraordinaire, plus il a besoin d’être appuyé de fortes preuves (Pierre-Simon Laplace)

1810: The more extraordinary a fact, the more it needs to be supported by strong proofs (Translation of Pierre-Simon Laplace)

1824: Extraordinary claims can rest only on extraordinary proofs (William Craig Brownlee)

1826: For extraordinary facts, we should have extraordinary evidence

1852: Extraordinary claims should be backed by extraordinary proof

1854: An extraordinary, an unnatural event, demands extraordinary evidence (F. B. Barton)

1871: Extraordinary evidence is needed to establish extraordinary facts (William Denton)

1895: Extraordinary claims always call for extraordinary proof (Ely Vaughn Zollars)

1906: Wonderful phenomena need wonderful evidence in their support (Joseph F. Rinn)

1975: Extraordinary claims require extraordinary proof (Marcello Truzzi)

1976: Extraordinary proof is necessary for extraordinary claims (Kendrick Frazier credited Marcello Truzzi)

1977: Extraordinary claims require extraordinary evidence (Carl Sagan)

1979: Extraordinary claims demand extraordinary proof. (James Oberg)

Below are selected citations in chronological order.

In 1708 Benjamin Bayly, Rector of St. James Church in Bristol, England published a book titled “An Essay on Inspiration”. Bayly discussed contemporary people who claimed to have received revelations about topics such as the end of the world directly from God. Bayly expressed skepticism. Boldface added to excerpts by QI:^[1] 1708, An Essay on Inspiration by Benjamin Bayly (Rector of St. James in Bristol), Part 2 of 2, Second Edition, Quote Page 362, Printed by J. M. for John Wyat, London. (Google Books Full View) link

Sure, these Matters being very extraordinary, will require a very extraordinary Proof ….

In 1738 “The Gentleman’s Magazine” published a piece from a correspondent who discussed the evidence required to believe remarkable facts particularly in the religious domain:^[2]1738 March, The Gentleman’s Magazine, Volume 8, Correspondence sent to Editor Sylvanus Urban: The Christian Revelation Set in a New Light, Start Page 125, Quote Page 127, Column 2, Printed by … Continue reading

But as it is a Matter of an extraordinary Kind, it is but reasonable in us to require extraordinary Evidence for it. And this we have, as great as possibly can be given, in the Miracles of Jesus.

In 1740 Anglican religious writer Arthur Ashley Sykes published “The Principles and Connexion of Natural and Revealed Religion Distinctly Considered”. He discussed the evidence needed to believe remarkable facts:^[3]1740, The Principles and Connexion of Natural and Revealed Religion Distinctly Considered by Arthur Ashley Sykes, Chapter: Preface, Quote Page vi, Printed for J. and P. Knapton, London. (Google Books … Continue reading

As every Man has a Right to demand extraordinary Evidence for any extraordinary Fact, and particularly for such an extraordinary Fact as Revelation is, such is here produced …

In 1741 the posthumous book “Select Discourses on Moral and Religious Subjects” by Reverend John Straight included the following:^[4]1741, Select Discourses on Moral and Religious Subjects by the Reverend Mr. John Straight (Late Vicar of Finden in Sussex, and some time Fellow of Magdalen College, Oxon), Volume 1 of 2, Discourse 1: … Continue reading

Assertions so contrary to Fact, so repugnant to the Experience of Mankind from first to last, require some extraordinary Proof to gain our Credit and Assent.

In 1748 David Hume published “Philosophical Essays Concerning Human Understanding” which included an essay titled “Of Miracles” containing the following thematically related saying:^[5] 1748, Philosophical Essays Concerning Human Understanding by David Hume, Essay 10: Of Miracles, Start Page 173, Quote Page 175, Printed for A. Millar, London. (Google Books Full View) link

A wise Man, therefore, proportions his Belief to the Evidence.

David Hume’s 1948 essay “Of Miracles” also contained the following statements:^[6] 1748, Philosophical Essays Concerning Human Understanding by David Hume, Essay 10: Of Miracles, Start Page 173, Quote Page 182, Printed for A. Millar, London. (Google Books Full View) link

The plain Consequence is (and ’tis a general Maxim worthy of our Attention) “That no Testimony is sufficient to establish a Miracle, unless the Testimony be of such a Kind, that its Falsehood would be more miraculous, than the Fact, which it endeavours to establish: And even in that Case, there is a mutual Destruction of Arguments, and the Superior only gives us an Assurance suitable to that Degree of Force, which remains, after deducting the Inferior.”

In 1800 the Lord Bishop of London Beilby Porteus published “A Summary of the Principal Evidences for the Truth and Divine Origin of the Christian Revelation”. He included the following comment about miracles:^[7]1800, A Summary of the Principal Evidences for the Truth and Divine Origin of the Christian Revelation by Beilby Porteus (Lord Bishop of London), Second Edition, Chapter: On the Truth and Divine … Continue reading

It is true, that miracles being very unusual and extraordinary facts, they require very strong evidence to support them; much stronger, it must be owned, than common events, that are recorded in history …

In 1804 religious writer Elihu Palmer published “Prospect: Or, View of the Moral World” which included a remark about the credibility of supernatural events:^[8]1804 March 31, Prospect: Or, View of the Moral World by Elihu Palmer, Volume 1, Number 17, Section: Miracles, Quote Page 133, Printed for The Editor Elihu Palmer, New York. (Google Books Full View) … Continue reading

I ought to have extraordinary evidence, to induce me to believe extraordinary things, that are supernatural, which cannot be so credible as ordinary things which are natural.

In 1810 mathematician Pierre-Simon Laplace published an essay about probability within an annual astronomical book, and he employed the saying. Here is an excerpt in French followed by an English translation:^[9]1810, Annuaire Présenté A. S. M. L’Empereur at Roi Par Les Bureau des Longitudes, Pour L’An 1811, Article: Notice Sur Les Probabilités, by Pierre-Simon Laplace, Start Page 98, Quote … Continue reading

De là nous devons généralement conclure que plus un fait est extraordinaire, plus il a besoin d’être appuyé de fortes preuves; car ceux qui l’attestent, pouvant ou tromper, ou avoir été trompés, ces deux causes sont d’autant plus probables, que la réalité du fait l’est moins en elle-même.

From this we must generally conclude that the more extraordinary a fact, the more it needs to be supported by strong proofs; for those who attest it, being able either to deceive, or to have been deceived, these two causes are all the more probable, as the reality of the fact is less in itself.

In 1814 Laplace published “Essai Philosophique sur Les Probabilités” (“Philosophical Essay on Probability”) which was similar to the earlier essay:^[10]1814, Essai Philosophique sur Les Probabilités by M. Le Comte Laplace (Pierre-Simon Laplace), Quote Page 12, Mme Ve Courcier, Imprimeur-Libraire pour les Mathématiques, Paris, France. (Google Books … Continue reading

De ce qui précède, nous devons généralement conclure que plus un fait est extraordinaire, plus il a besoin d’être appuyé de fortes preuves.

From what precedes, we ought generally to conclude that the more extraordinary the event, the greater the need of its being supported by strong proofs.

In 1824 religious figure William Craig Brownlee published “A Careful and Free Inquiry Into the True Nature and Tendency of the Religious Principles of the Society of Friends” which included the following:^[11]1824, A Careful and Free Inquiry Into the True Nature and Tendency of the Religious Principles of the Society of Friends, Commonly Called Quakers by William Craig Brownlee (Minister of the Gospel), … Continue reading

Let us see the commanding proofs of their miraculous or prophetical powers? This is what the church demanded in every age; and this was unhesitatingly complied with by every true prophet. It is as reasonable now as in ancient times. Extraordinary claims can rest only on extraordinary proofs. Ordinary claims are supported by common proofs.

In 1826 a religious periodical called “The Register” based in Orbiston, North Lanarkshire, Scotland printed the following:^[12]1826 January 26, The Register For The First Society of Adherents to Divine Revelation at Orbiston in Lanarkshire, Number 10, The Seven Lessons: The First Lesson, Quote Page 76, Column 2, Printed at … Continue reading

“To affirm that any alleged fact is unnatural, or contrary to the laws of nature, because it differs from the order of things with which we are familiar, would be to contract human knowledge within very narrow limits: all that can be reasonably demanded is, that for extraordinary facts, we should have extraordinary evidence.”

In 1852 the “New York Observer” printed a note from a correspondent containing the following:^[13] 1852 June 17, New York Observer and Chronicle, Volume 30, Issue 25, What I Saw of Popery by Correspondent E., (Note sent to the New York Observer), Quote Page 1, Column 2, New York. (ProQuest)

Nor do I expect too much, for whether in a court of law, or at the tribunal of common sense, it is sound doctrine, that extraordinary claims should be backed by extraordinary proof.

In 1854 “The Reasoner: Gazette of Secularism” printed a piece by F. B. Barton containing the following passage:^[14]1854 July 16, The Reasoner: Gazette of Secularism, On the Law of Association as Regards Freethinking by F. B. Barton, Start Page 38, Quote Page 40, Holyoake and Company, London. (Google Books Full … Continue reading

An ordinary occurrence may be believed on ordinary evidence, but an extraordinary, an unnatural event, demands extraordinary evidence, evidence that shall outweigh the improbability of that which is required to be believed. It is a law of the human mind to be unwilling to credit that which is contrary to all its experience.

In 1871 William Denton published “Is Spiritualism True?”, and he employed an instance of the saying:^[15] 1871 Copyright, Is Spiritualism True? by William Denton, Quote Page 9, Published by William Denton, Boston, Massachusetts. (Google Books Full View) link

Such evidence as this might be considered sufficient to establish the fact of clairvoyance; but extraordinary evidence is needed to establish extraordinary facts.

In 1895 Ely Vaughan Zollars, President of Hiram College in Ohio, published “The Great Salvation” which contained the following:^[16]1895, The Great Salvation by Ely V. Zollars (Ely Vaughan Zollars, President of Hiram College), Chapter 5: The Beginning of the Kingdom of God, Quote Page 78, The Standard Publishing Company, … Continue reading

Extraordinary claims always call for extraordinary proof. Christ, the King, makes the most wonderful claims. He deliberately claims divinity.

In 1902 an English translation of Pierre-Simon Laplace’s work under the title “A Philosophical Essay on Probabilities” appeared:^[17]1902, A Philosophical Essay on Probabilities by Pierre Simon, Marquis de Laplace, (Translated from the Sixth French Edition), Translated by Frederick Wilson Truscott and Frederick Lincoln Emory, … Continue reading

From what precedes, we ought generally to conclude that the more extraordinary the event, the greater the need of its being supported by strong proofs. For those who attest it, being able to deceive or to have been deceived, these two causes are as much more probable as the reality of the event is less.

In 1906 “The New York Times” printed a quotation from skeptic and magician Joseph Rinn:^[18] 1906 January 17, New York Times, Topics of the Times, Quote Page 10, Column 4, New York. (ProQuest)

“Being courteous does not necessitate being a fool, and if conditions that permit fraud are necessary for the production of psychic phenomena, we had better quit investigations. Wonderful phenomena need wonderful evidence in their support to be of any value so far as truth is concerned, otherwise they are valueless.”

In 1975 “Parapsychology Review” printed a letter from sociologist and magician Marcello Truzzi which contained an instance of the saying:^[19]1975 November-December, Parapsychology Review, Letter from Marcello Truzzi, Quote Page 24 and 25, Published bimonthly by Parapsychology Foundation Inc., New York. (Not yet verified; Text visible in … Continue reading

There are numerous other differences I might point out between Mr. Cox and myself, but they almost all revolve around the central issue I have argued: Extraordinary claims require extraordinary proof.

In 1976 “Science News” published an article titled “Science and the Parascience Cults” by Kendrick Frazier who interviewed Truzzi. Frazier printed a slightly different instance while crediting Truzzi:^[20]1976 May 29, Science News, Volume 109, Number 22, Science and the Parascience Cults by Kendrick Frazier, Start Page 346, Quote Page 347, Column 3, Published by Society for Science & the Public. … Continue reading

He proposes two additional principles important in dealing with anomalous claims: First, the burden of proof is on those who claim the existence of an anomaly; second, extraordinary proof is necessary for extraordinary claims.

In 1977 “The Washington Post” published the following quotation from astronomer Carl Sagan:^[21] 1977 December 16, The Washington Post, Section: Weekend, Second View: Sagan on ‘Encounters’ by Art Harris, Start Page 1, Quote Page 1, Column 3, Washington D.C. (ProQuest)

Sagan scoffs. “There’s not a smidgen of evidence to suggest that lights in the sky or the disappearance of ships or planes are due to extraterrestrial intervention. The return of those planes is a favorite incident of the most uncritical panderers of the Bermuda Triangle mysteries. Extraordinary claims require extraordinary evidence.”

In 1979 Carl Sagan printed an instance in his book “Broca’s Brain: Reflections on the Romance of Science”:^[22]1979, Broca’s Brain: Reflections on the Romance of Science by Carl Sagan, Chapter 5: Night Walkers and Mystery Mongers — Sense and Nonsense at the Edge of Science, Quote Page 62, Random … Continue reading

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

Also, in 1979 “New Scientist” published an article by space journalist James Oberg which included an instance of the saying:^[23]1979 October 11, New Scientist, The failure of the ‘science’ of ufology by James Oberg, Start Page 102, Quote Page 105, Column 1, Published by Reed Business Information. London. (Google Books … Continue reading

And yet the rules of science are clear: extraordinary claims demand extraordinary proof.

In 1999 science fiction author Arthur C. Clarke published a collection of essays titled “Greetings, Carbon-Based Bipeds!” Clarke attributed the saying to Sagan:^[24]1999, Greetings, Carbon-Based Bipeds!: Collected Essays 1934-1998 by Arthur C. Clarke, Edited by Ian T. Macauley, Part 7: Postscript: 2000 and Beyond, Essay 1: Science and Society (Bibliographic … Continue reading

I remained interested but skeptical, agreeing with Carl Sagan’s principle that “extraordinary claims require extraordinary proofs” (spoken in connection with UFOs and alien visitors, a whole supermarket shelf of worm cans, none of which I intend to open here).

In 2012 skeptic Daniel Loxton published an essay titled “Wonderful Phenomena Demand Wonderful Evidence”, and he included germane citations for Pierre-Simon Laplace, David Hume, Marcello Truzzi, Carl Sagan and others.^[25]Website: SkepticBlog, Article title: Wonderful Phenomena Demand Wonderful Evidence, Article author: Daniel Loxton, Date on website: December 11, 2012 , Website description: SkepticBlog is a … Continue reading

In conclusion, this saying has been in circulation for at least a few hundred years. It is difficult to trace because the vocabulary and phrasing has evolved over time. An overview is presented at the beginning of this article. In modern times, it was popularized by Marcello Truzzi and Carl Sagan.

(Great thanks to Hugh Henry and Massimo Fuggetta whose inquiries led QI to formulate this question and perform this exploration. Additional thanks to researchers Daniel Loxton, Bill Mullins, Peter Morris, and Fred R. Shapiro. Loxton located several of the citations presented above as did Mullins, Morris, and Shapiro. Also, thanks to mailing list discussants Stephen Goranson, Jonathan Lighter, and Wilson Gray. Thanks to Kam-Yung Soh for pointing out a typo. Further thanks to Massimo Fuggetta who suggested adding the Hume citations.)

Update History: On December 9, 2021 the two 1748 citations for David Hume were added to the article, and the 2012 Daniel Loxton citation was also added to the article.