Quotations by Feynman, Richard


The first principle is that you must not fool yourself — and you are the easiest person to fool.

Richard Feynman (1918-1988) American physicist
“Cargo Cult Science,” commencement address, California Institute of Technology (1974)
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But there is one feature I notice that is generally missing in Cargo Cult Science. That is the idea that we all hope you have learned in studying science in school — we never explicitly say what this is, but just hope that you catch on by all the examples of scientific investigation. It is interesting, therefore, to bring it out now and speak of it explicitly. It’s a kind of scientific integrity, a principle of scientific thought that corresponds to a kind of utter honesty — a kind of leaning over backwards. For example, if you’re doing an experiment, you should report everything that you think might make it invalid — not only what you think is right about it: other causes that could possibly explain your results; and things you thought of that you’ve eliminated by some other experiment, and how they worked — to make sure the other fellow can tell they have been eliminated.

Richard Feynman (1918-1988) American physicist
“Cargo Cult Science,” commencement address, California Institute of Technology (1974)
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Details that could throw doubt on your interpretation must be given, if you know them. You must do the best you can — if you know anything at all wrong, or possibly wrong — to explain it. If you make a theory, for example, and advertise it, or put it out, then you must also put down all the facts that disagree with it, as well as those that agree with it. There is also a more subtle problem. When you have put a lot of ideas together to make an elaborate theory, you want to make sure, when explaining what it fits, that those things it fits are not just the things that gave you the idea for the theory; but that the finished theory makes something else come out right, in addition. In summary, the idea is to try to give all of the information to help others to judge the value of your contribution; not just the information that leads to judgment in one particular direction or another.

Richard Feynman (1918-1988) American physicist
“Cargo Cult Science,” commencement address, California Institute of Technology (1974)
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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.

Richard Feynman (1918-1988) American physicist
“What Is and What Should Be the Role of Scientific Culture in Modern Society,” lecture at the Galileo Symposium, Italy (1964)
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Science is the belief in the ignorance of the experts.

Richard Feynman (1918-1988) American physicist
“What Is Science?” address, National Science Teachers Association, New York (1966)
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Science is like sex: sometimes something useful comes out, but that is not the reason we are doing it.

Richard Feynman (1918-1988) American physicist
(Attributed)

Many variations can be found for this quotation (none of them with citation); the word "Science" and "Physics" are often interchanged:
  • "Science is like sex, it has its practical purposes, but that's not why we do it."
  • "Science is like sex. Sometimes something useful comes out, but that is not why we are doing it."
  • Physics is like sex. Sure, it may give some practical results, but that's not why we do it."
As noted here, Frank Oppenheimer (a colleague of Feynman's) was quoted saying, "There's a lot of practical fruits to understanding, but it's like sex. There are practical fruits to sex, but nobody would say that's why you do it, normally." Feynman and Oppenheimer may well have collaborated on the general phrasing, or taken it from one another.
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For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.

Richard Feynman (1918-1988) American physicist
Rogers Commission Report into the Challenger Crash, Appendix F “Personal Observations on Reliability of Shuttle” (Jun 1986)

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When playing Russian roulette the fact that the first shot got off safely is little comfort for the next.

Richard Feynman (1918-1988) American physicist
Rogers Commission Report into the Challenger Crash, Appendix F “Personal Observations on Reliability of Shuttle” (Jun 1986)

Full report
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The inexperienced, and crackpots, and people like that, make guesses that are simple, but you can immediately see that they are wrong, so that does not count. Others, the inexperienced students, make guesses that are very complicated, and it sort of looks as if it is all right, but I know it is not true because the truth always turns out to be simpler than you thought.

Richard Feynman (1918-1988) American physicist
The Character of Physical Law, ch 7 “Seeking New Laws” (1965)
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So we have to make guesses in order to give any utility at all to science. In order to avoid simply describing experiments that have been done, we have to propose laws beyond their observed range. There is nothing wrong with that, despite the fact that it makes science uncertain. If you thought before that science was certain — well, that is just an error on your part.

Richard Feynman (1918-1988) American physicist
The Character of Physical Law, ch. 3 “The Great Conservation Principles” (1965)
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For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy.

Richard Feynman (1918-1988) American physicist
The Character of Physical Laws ch. 3 “The Great Conservation Principles” (1965)
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We cannot define anything precisely! If we attempt to, we get into that paralysis of thought that comes to philosophers who sit opposite each other, one saying to the other, “You don’t know what you are talking about!”. The second one says, “What do you mean by know? What do you mean by talking? What do you mean by you?” and so on.

Richard Feynman (1918-1988) American physicist
The Feynman Lectures on Physics, Volume I, 8-2 “Motion” (20 Oct 1961)
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I have argued flying saucers with lots of people. … I was interested in this: they keep arguing that it is possible. And that’s true. It is possible. They do not appreciate that the problem is not to demonstrate whether it’s possible or not, but whether it’s going on or not. Whether it’s probably occurring or not, not whether it could occur.

Richard Feynman (1918-1988) American physicist
The Meaning of It All (1998)
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No government has the right to decide on the truth of scientific principles, nor to prescribe in any way the character of the questions investigated. Neither may a government determine the aesthetic value of artistic creations, nor limit the forms of literacy or artistic expression. Nor should it pronounce on the validity of economic, historic, religious, or philosophical doctrines. Instead it has a duty to its citizens to maintain the freedom, to let those citizens contribute to the further adventure and the development of the human race.

Richard Feynman (1918-1988) American physicist
The Meaning of It All, “The Uncertainty of Values” (1999)
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It doesn’t seem to me that this fantastically marvelous universe, this tremendous range of time and space and different kinds of animals, and all the different planets, and all these atoms with all their motions, and so on, all this complicated thing can merely be a stage so that God can watch human beings struggle for good and evil — which is the view that religion has. The stage is too big for the drama.

Richard Feynman (1918-1988) American physicist
Viewpoint interview by Bill Stout, KNXT (1 May 1959)

Reprinted in Perfectly Reasonable Deviations from the Beaten Track, ed. by Michelle Feynman, Appendix I (2006).
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Scientists take it for granted that it is perfectly consistent to be unsure — that it is possible to live and not know. But I don’t know whether everyone realizes that this is true.

Richard Feynman (1918-1988) American physicist
What Do You Care What Other People Think? (1988)
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Although my mother didn’t know anything about science, she had a great influence on me as well. In particular, she had a wonderful sense of humor, and I learned from her that the highest forms of understanding we can achieve are laughter and human compassion.

Richard Feynman (1918-1988) American physicist
What Do You Care What Other People Think?, “The Making of a Scientist” (1988)
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It doesn’t seem to me that this fantastically marvelous universe, this tremendous range of time and space and different kinds of animals, and all the different planets, and all these atoms with all their motions, and so on, all this complicated thing can merely be a stage so that God can watch human beings struggle for good and evil — which is the view that religion has. The stage is too big for the drama.

Richard Feynman (1918-1988) American physicist
Comment (1959)

Quoted in J. Gleick, Genius: The Life and Science of Richard Feynman (1992)

Added on 21-Oct-08 | Last updated 21-Oct-08
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