Clarke's three laws
- When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
- The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
- Any sufficiently advanced technology is indistinguishable from magic.
All three laws appear in Clarke's essay "Hazards of Prophecy: The Failure of Imagination", first published in Profiles of the Future (1962).
Clarke's first law was proposed by Clarke in the 1962 edition of the essay, as "Clarke's Law".
The second law is offered as a simple observation in the same essay. Its status as Clarke's second law was conferred by others. In the 1973 revision of Profiles of the Future, Clarke acknowledged it as his second law and proposed the third, writing "As three laws were good enough for Newton, I have modestly decided to stop there".
The third law, despite being latest stated by a decade, is the best known and most widely cited. It appears only in the 1973 revision of the "Hazards of Prophecy" essay. It echoes a statement in a 1942 story by Leigh Brackett: "Witchcraft to the ignorant, … simple science to the learned". Earlier examples of this sentiment may be found in Wild Talents (1932) by Charles Fort: "...a performance that may some day be considered understandable, but that, in these primitive times, so transcends what is said to be the known that it is what I mean by magic," and in the short story The Hound of Death (1933) by Agatha Christie: "The supernatural is only the natural of which the laws are not yet understood."
Clarke gave an example of the third law when he said that while he "would have believed anyone who told him back in 1962 that there would one day exist a book-sized object capable of holding the content of an entire library, he would never have accepted that the same device could find a page or word in a second and then convert it into any typeface and size from Albertus Extra Bold to Zurich Calligraphic", referring to his memory of "seeing and hearing Linotype machines which slowly converted ‘molten lead into front pages that required two men to lift them’".
Proposed fourth law
A fourth law has been proposed for the canon, despite Clarke's declared intention of stopping at three laws. Geoff Holder quotes: "For every expert, there is an equal and opposite expert," which is part of American economist Thomas Sowell's "For every expert, there is an equal and opposite expert, but for every fact there is not necessarily an equal and opposite fact", from his 1995 book The Vision of the Anointed. 
Variants of the third law
The third law has inspired many snowclones and other variations:
- Any sufficiently advanced extraterrestrial intelligence is indistinguishable from God. (Shermer's last law)
- Any sufficiently advanced act of benevolence is indistinguishable from malevolence (referring to artificial intelligence).
- The following two variants are very similar, and combine the third law with Hanlon's razor
- Any sufficiently advanced troll is indistinguishable from a genuine kook or the viewpoints of even the most extreme crank are indistinguishable from sufficiently advanced satire (Poe's law).
- Any sufficiently advanced technology is indistinguishable from a rigged demo.
- Any sufficiently advanced idea is distinguishable from mere magical incantation provided the former is presented as a mathematical proof, verifiable by sufficiently competent mathematicians.
- Any sufficiently crappy research is indistinguishable from fraud (Andrew Gelman).
A contrapositive of the third law is
- Any technology distinguishable from magic is insufficiently advanced. (Gehm's corollary)
The third law has been:
- reversed for fictional universes involving magic: "Any sufficiently analyzed magic is indistinguishable from science!" or "Any sufficiently arcane magic is indistinguishable from technology."
- expanded for fictional universes focusing on science fiction: "Any technology, no matter how primitive, is magic to those who don't understand it."
- "'Hazards of Prophecy: The Failure of Imagination'" in the collection Profiles of the Future: An Enquiry into the Limits of the Possible (1962, rev. 1973), pp. 14, 21, 36.
- Clarke, Arthur C. (1973). Profiles of the Future: An Inquiry into the Limits of the Possible. Popular Library. ISBN 9780330236195.
- "The Sorcerer of Rhiannon", Astounding February 1942, p. 39.
- Philip Gooden (2015). Skyscrapers, Hemlines and the Eddie Murphy Rule: Life's Hidden Laws, Rules and Theories. Bloomsbury Publishing. p. 83. ISBN 9781472915030.
- Holder, Geoff (2009). 101 Things to Do with a Stone Circle. The History Press, 2009. Holder offers as his source Clarke's Profiles of the Future (Millennium Edition, 1999, paperback edition page 143, ISBN 0-575-40277-6).
- Massimo Pigliucci, Nonsense on Stilts: How to Tell Science from Bunk, 2010, ISBN 0226667871; an epigraph to Chapter 12, p. 279
- Shermer, Michael (2002-01-01). "Shermer's Last Law". Scientific American. (Subscription required (. ))
- Rubin, Charles T. (5 November 2008). "What is the Good of Transhumanism?". In Chadwick, Ruth; Gordijn, Bert. Medical Enhancement and Posthumanity (PDF). Springer. p. 149. ISBN 9789048180059. Archived (PDF) from the original on 16 October 2014. Retrieved 17 October 2014.
Rubin is referring to an earlier work of his:
Rubin, Charles T. (1996). "First contact: Copernican moment or nine day's wonder?". In Kingsley, Stuart A.; Lemarchand, Guillermo A. The Search for Extraterrestrial Intelligence (SETI) in the Optical Spectrum II: 31 January-1 February 1996, San Jose, California, Band 2704. Proceedings of SPIE – the International Society for Optical Engineering. Bellingham, WA: SPIE—The International Society for Optical Engineering. pp. 161–184. ISBN 978-0-8194-2078-7.
- J. Porter Clark (16 November 1994). "Clark's Law". Newsgroup: alt.news.misc. Retrieved 2014-12-10.
They were apologetic and seemed sincere, but sufficiently advanced cluelessness is indistinguishable from malice. 8-)
- Quote Details: James Klass: Any sufficiently advanced technology... - The Quotations Page
- Conesa-Sevilla, J. (2016). Ecopsychology Revisited: For Whom do the Nature Bells Toll? (Ch. 8, pg. 256)
- Andrew Gelman. Clarke’s Law: Any sufficiently crappy research is indistinguishable from fraud (20 June 2016).
- Leeper, Evelyn; Leeper, Mark (5 November 2004). "Correction". The MT Void. Mt. Holz Science Fiction Society. 23 (19). Archived from the original on 2004-12-29. Retrieved 2015-11-29.
- Girl Genius
- Sufficiently Analyzed Magic – TV Tropes
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- Freefall 00255 November 12, 1999