“Clarke's Third Law: Any sufficiently advanced technology is indistinguishable from magic.”

Source: PsyberMagick (1995), p. 15

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This is derived from the third of Arthur C. Clarke's three laws : "Any sufficiently advanced technology is indistinguishable from magic." There are other variants which had inverted this including one known as Gehm's corollary http://www-users.cs.york.ac.uk/susan/cyc/l/law.htm, published several years earlier : "Any technology distinguishable from magic is insufficiently advanced." The earliest variant seems to be "Any sufficiently advanced magic is indistinguishable from technology." It has been called "Niven's Law" and attributed to Larry Niven by some, and to Terry Pratchett by others, but without any citation of an original source in either case — the earliest occurrence yet located is an anonymous one in Keystone Folklore (1984) by the Pennsylvania Folklore Society.
Foundation's Fear (1997)

Source: The Laundry Files, The Jennifer Morgue (2006), Chapter 12, “Power Breakfast” (p. 254)

Source: Pushing Ice (2005), Chapter 30 (p. 435)

in his Nobel Lecture http://nobelprize.org/nobel_prizes/physics/laureates/2000/kroemer-lecture.html, Quasi-Electric Fields and Band Offsets: Teaching Electrons New Tricks, 8 December 2000, at Aula Magna, Stockholm University.

The Promise of Space http://books.google.com/books?id=FWwhAAAAMAAJ&dq=The+Promise+of+Space&ei=ab0yR__TKZzuoAL_mf3RDw&ie=ISO-8859-1&pgis=1 (1968); This and similar statements attributed to Mahatma Gandhi and J. B. S. Haldane may ultimately be derived from a statement attibuted to Arthur Schopenhauer:
On Clarke's Laws
Context: Clarke's Law of Revolutionary Ideas: Every revolutionary idea — in science, politics, art, or whatever — seems to evoke three stages of reaction. They may be summed up by the phrases:(1) "It's completely impossible — don't waste my time";
(2) "It's possible, but it's not worth doing";
(3) "I said it was a good idea all along."

From Hawking's article A Brief History of Relativity http://www.time.com/time/magazine/article/0,9171,993018-6,00.html, in Time magazine (31 December 1999)