Feynman quotes, checked

Feynman is one of the most quoted scientists there is, and plenty of the lines credited to him are things he never said. Each page below takes one popular quote back to its original source: the book and page, the lecture, the report. So far we have checked 9 quotes: 1 misattributed, 3 paraphrased, 5 real.

• Misattributed “Shut up and calculate!” Misattributed. Nobody has found a source in which Feynman says it. The earliest known use is a 1989 column by physicist N. David Mermin.
• Paraphrased “If you can’t explain something to a first-year student, then you haven’t really understood it.” Paraphrased from a story. According to David Goodstein (Physics Today, 1989), Feynman said “I couldn’t reduce it to the freshman level. That means we really don’t understand it.” He was talking about one topic, not stating a rule.
• Paraphrased “If you think you understand quantum mechanics, you don’t understand quantum mechanics.” Paraphrased. The popular version isn’t in his books. What he said was “I think I can safely say that nobody understands quantum mechanics.”
• Paraphrased “It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with experiment, it’s wrong.” Paraphrased, but close. In The Character of Physical Law (chapter 7, p. 156) Feynman says “It does not make any difference how beautiful your guess is”. The popular version swaps “guess” for “theory”.
• Real “For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.” Real, word for word. It’s the closing sentence of Feynman’s appendix to the presidential commission’s report on the Challenger accident (1986).
• Real “I learned very early the difference between knowing the name of something and knowing something.” Real. Feynman said it in his 1981 BBC Horizon interview about his father, in slightly different word order: “he knew the difference between knowing the name of something and knowing something, which I learnt very early.”
• Real “Science is the belief in the ignorance of experts.” Real. It comes from Feynman’s talk “What Is Science?”, given to science teachers in 1966 and published in The Physics Teacher in 1969.
• Real “The first principle is that you must not fool yourself — and you are the easiest person to fool.” Real, word for word. It comes from Feynman’s 1974 Caltech commencement address, “Cargo Cult Science”.
• Real “What I cannot create, I do not understand.” Real, in his own chalk. It is the top line of Feynman’s blackboard as it was photographed after his death in 1988 (Caltech Archives, Images 1.10-29).

How we check: we look for the original book and page, lecture, letter, recording or report. Real means the words are in Feynman’s own work; paraphrased means he said something close; misattributed means someone else said it first; no reliable source found means we couldn’t trace it. Also on Feynmanpedia: myth tests.