By Richard Feynman

Adapted from the Caltech commencement address given in 1974

During the Middle Ages there were all kinds of crazy ideas,
such as that a piece of rhinoceros horn would increase
potency.  Then a method was discovered for separating the
ideas--which was to try one to see if it worked, and if it
didn't work , to eliminate it.  This method became organized,
of course, into science.  And it developed very well, so that
we are now in the scientific age.  It is such a scientific age,
in fact, that we have difficulty in understanding how witch
doctors could ever have existed, when nothing that they 
proposed ever really worked--or very little of it did.
       But even today I meet lots of people who sooner or later
get me into a conversation about UFO's, or astrology, or some
form of mysticism, expanded consciousness, new types of
awareness, ESP, and so forth.  And I've concluded that it's not
a scientific world.
      Most people believe so many wonderful things that I
decided to investigate why they did.  And what has been
referred to as my curiosity for investigation has landed me in
a difficulty where I found so much junk that I'm overwhelmed.
First I started out by investigating various ideas of mysticism,
and mystic experiences.  I went into isolation tanks and got
many hours of hallucinations, so I know something about
that.  Then I went to Esalen, which is a hotbed of this kind of 
thought (it's a wonderful place; you should go visit there).
Then I became overwhelmed.  I didn't realize how much 
there was.
      At Esalen there are some large baths fed by hot springs
situated on a ledge about thirty feet above the ocean.  One of
my most pleasurable experiences has been to sit in one of
thosse baths and watch the waves crashing onto the rocky
shore below, to gaze into the clear blue sky above, and to
study a beautiful nude as she quietly appears and settles into
the bath with me.
      One time I sat down in a bath where there was a
beautiful girl sitting with a guy who didn't seem to know her.
Right away I began thinking, "Gee! How am I gonna get
started talking to this beautiful nude babe?"
      I'm trying to figure out what to say, when the guy says to
her, "I'm, uh, studying massage. Could I practice on you?"
      "Sure, she says.  They get out of the bath and she lies
down on a massage table nearby.
      I think to myself, "What a nifty line! I can never think of
anything like that!"  He starts to rub her big toe.  "I think I
feel it," he says.  "I feel a kind of dent--is that the pitui-
tary?"
      I blurt out, "You're a helluva long way from the pituitary,
man!"
      They looked at me, horrified--I had blown my cover--and
said, "It's reflexology!"  I quickly closed my eyes and appeared
to be meditating.
      That's just an example of the kind of things that over-
whelm me.  I also looked into the extra sensory perception and
PSI phenomena, and the latest craze there was Uri Geller, a
man who is supposed to be able to bend keys by rubbing
them with his finger.  So I went to his hotel room on his
invitation, to see a demonstration of both mindreading and
bending keys.  He didn't do any mindreading that succeeded;
nobody can read my mind, I guess.  And my boy held a key
and Geller rubbed it, and nothing happened.  Then he told us 
it works better under water, and so you can picture all of us
standing in the bathroom with the water turned on and the
key under it, and him rubbing the key with his finger.
Nothing happened.  So I was unable to investigate that
phenomenon.
      But then I began to think, what else is there that we
believe?  (And I thought then about the witch doctors, and
how easy it would have been to check on them by noticing
that nothing really worked.)  So I found things that even more
people believe, such as that we have some knowledge of how
to educate.  There are big schools of reading methods and
mathematics methods, and so forth, but if you notice, you'll
see the reading scores keep going down--or hardly going
up--in spite of the fact that we continually use these same
people to improve the methods.  There's a witch doctor
remedy that doesn't work.  It ought to be looked into; how do
they know that their method should work?  Another example
is how to treat criminals.  We obviously have made no progress
--lots of theory, but no progress--in decreasing the amount of
crime by the method that we use to handle criminals.
      Yet these things are said to be scientific.  We study them.
And I think ordinary people with commonsense ideas are
intimidated by this pseudoscience.  A teacher who has some 
good idea of how to teach her children to read is forced by
the school system to do it some other way--or is even fooled
by the school system into thinking that her method is not
necessarily a good one.  Or a parent of bad boys, after
disciplining them in one way or another, feels guilty for the
rest of her life because she didn't do "the right thing."
According to the experts.
      So we really ought to look into theories that don't work,
and science that isn't science.
      I think the educational and psychological studies I
mentioned are examples of what I would like to call cargo cult
science.  In the south seas there is a cargo cult of people.
During the war they saw airplanes land with lots of good
materials, and they want the same thing to happen now.  So
they've arranged to make things like runways, to put fires
along the sides of the runways, to make a wooden hut for a
man to sit in, with two wooden pieces on his head like
headphones and bars of bamboo sticking out like antennas--
he's the controller--and they wait for the airplanes to land.
They're doing everything right.  The form is perfect.  It looks
exactly the way it looked before. But it doesn't work.  No
airplanes land.  So I call these things cargo cult science,
because they follow all the apparent precepts and forms of
scientific investigation, but they're missing something essen-
tial, because the planes don't land.
      Now it behooves me, of course, to tell you what they're
missing.  But it would be just about as difficult to explain to
the South Sea Islanders how they have to arrange things so
that they get some wealth in their system.  It is not something
simple like telling them how to improve the shapes of the
earphones.  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 it 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.
       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 informa-
tion to help others to judge the value of your contribution;
not just the information that leads to judgement in one partic-
ular direction or another.
      The easiest way to explain this idea is to contrast it, for
example, with advertising.  Last night I heard that Wesson oil
doesn't soak through food.  Well, that's true.  It's not dishon-
est; but the thing I'm talking about is not just a matter of not
being dishonest, it's a matter of scientific integrity, which is
another level.  The fact that should be added to that advertis-
ing statement is that no oils soak through food, if operated at
a certain temperature.  If operated at another temperature,
they all will--including Wesson oil.  So it's the implication 
which has been conveyed, not the fact, which is true, and the
difference is what we have to deal with.
      We've learned from experience that the truth will come
out whether you were wrong or right.  Nature's phenome-
na will agree or they'll disagree with your theory.  And,
although you may gain some temporary fame and excit-
ment, you will not gain a good reputation as a scientist
if you haven't tried to be very careful in this kind of work.
And it's this type of integrity, this kind of care not to fool
yourself, that is missing to a large extent in much of the
research in cargo cult science.
      A great deal of their difficulty is, of course, the difficul-
ty of the subject and the inapplicability of the scientific method
to the subject.  Nevertheless, it should be remarked that this
is not the only difficulty.  That's why the planes don't land--
but they don't land.
      We have learned a lot from experience about how to
handle some of the ways we fool ourselves.  One example:
Millikan measured the charge on an electron by an experi-
ment with falling oil drops, and got an answer which we now
know not to be quite right.  It's a little bit off, because he had
the incorrect value for the viscosity of air.  It's interesting to
look at the history of measurements of the charge of the
electron, after Millikan.  If you plot them as a function of
time, you find that one is a little bigger than Millikan's, and
the next one's a little bit bigger than that, and the next one's
a little bit bigger than that, until finally they settle down to a
number which is higher.
      Why didn't they discover that the new number was
higher right away?  It's a thing that scientists are ashamed
of--this history--because it's apparent that people did things
like this: When they got a number that was too high above
Millikan's, they thought something must be wrong--and they
would look for and find a reason why something might be
wrong.  When they got a number closer to Millikan's value
they didn't look so hard.  And so they eliminated the numbers
that were too far off, and did other things like that.  We've 
learned those tricks nowadays, and now we don't have that
kind of a disease.
      But this long history of learning how to not fool ourselves
--of having utter scientific integrity--is, I'm sorry to say, 
something that we haven't specifically included in any particular
course that I know of.  We just hope you've caught on by osmosis.
      The first principle is that you must not fool yourself--
and you are the easiest person to fool.  So you have to be very
careful about that.  After you've not fooled yourself, it's easy
not to fool other scientists.  You just have to be honest in a
conventional way after that.
      I would like to add something that's not essential to the
science, but something I kind of believe, which is that you
should not fool the layman when you're talking as a scientist.
I am not trying to tell you what to do about cheating on your
wife, or fooling your girlfriend, or something like that, when
you're not trying to be a scientist, but just trying to be an
ordinary human being.  We'll leave those problems up to you
and your rabbi.  I'm talking about a specific, extra type of
integrity that is not lying, but bending over backwards to
show how you're maybe wrong, that you ought to have when
acting as a scientist.  And this is our responsibility as scien-
tists, certainly to other scientists, and I think to laymen.
      For example, I was a little surprised when I was talking
to a friend who was going to go on the radio.  He does work
on cosmology and astronomy, and he wondered how he would
explain what the applications of his work were.  "Well," I
said, "there aren't any."  He said, "Yes, but then we won't get
support for more research of this kind." I think that's kind of
dishonest.  If you're representing yourself as a scientist, then
you should explain to the layman what you're doing--and if 
they don't want to support you under those circumstances,
then that's their decision.
      One example of the principle is this: If you've made up
your mind to test a theory, or you want to explain some idea,
you should always decide to publish it, whichever way it
comes out.  If we only publish results of a certain kind, we can
make the argument look good.  We must publish both kinds of 
results.
      I say that's also important in giving certain types of
government advice.  Supposing a senator asked you for advice
about whether drilling a hole should be done in his state; and
you decide it would be better in some other state.  If you 
don't publish such a result, it seems to me you're not giving 
scientific advice.  You're being used.  If your answer happens
to come out in the direction the government or the politicians
like, they can use it as an argument in their favor; if it comes
out the other way, they don't publish it at all.  That's not
giving scientific advice.
      Other kinds of errors are more characteristic of poor
science.  When I was at Cornell, I often talked to the people
in the psychology department.  One of the students told me
she wanted to do an experiment that went something like 
this--it had been found by others that under certain circum-
stances, X, rats did something, A.  She was curious as to
whether, if she changed the circumstances to Y, they would
still do A.  So her proposal was to do the experiment under
circumstances Y and see if they still did A.
      I explained to her that it was necessary first to repeat in
her laboratory the experiment of the other person--to do it
under condition X to see if she could get result A, and
then change to Y and see if A changed.  Then she would know
that the real difference was the thing she thought she had
under control.
      She was very delighted with this new idea, and went to
her professor.  And his reply was, no, you cannot do that,
because the experiment has already been done and you
would be wasting time.  This was in about 1947 or so, and it
seems to have been the general policy then to not try to
repeat psychological experiments, but only to change the
conditions and see what happens.
      Nowadays there's a certain danger of the same thing
happening, even in the famous field of physics.  I was shocked
to hear of an experiment done at the big accelerator at the
National Accelerator Laboratory, where a person used deute-
rium.  In order to compare his heavy hydrogen results to what
might happen with light hydrogen, he had to use data from
someone else's experiment on light hydrogen, which was
done on different apparatus.  When asked why, he said it was
because he couldn't get time on the program (because there's
so little time and it's such expensive apparatus) to do the
experiment with light hydrogen on this apparatus because
there wouldn't be any new result.  And so the men in charge
of programs at NAL are so anxious for new results, in order to
get more money to keep the thing going for public relations
purposes, they are destroying--possibly--the value of the
experiments themselves, which is the whole purpose of the
thing.  It is often hard for the experimenters there to com-
plete their work as their scientific integrity demands.
      All experiments in psychology are not of this type,
however. For example, there have been many experiments
running rats through all kinds of mazes, and so on--with little
clear result.  But in 1937 a man named Young did a very
interesting one.   He had a long corridor with doors all along
one side where the rats came in, and doors along the other
side where food was.   He wanted to see if he could train
the rats to go in at the third door down from wherever he
he started them off.  No.  The rats went immediately to the door
where the food had been the time before.
      The question was, how did the rats know, because the
corridor was so beautifully built and so uniform, that this was
the same door as before?  Obviously there was something
about the door that was different from the other doors.  So he
painted the doors very carefully, arranging the textures on
the faces of the doors exactly the same.  Still the rats could
tell.  Then he thought maybe the rats were smelling the food,
so he used chemicals to change the smell after each run.  Still
the rats could tell.  Then he realized the rats might be able to
tell by seeing the lights and the arrangement in the laborato-
ry like any commonsense person. So he covered the corridor,
and still the rats could tell.
      He finally found that they could tell by the way the floor
sounded when they ran over it.  And he could only fix that by
putting his corridor in sand.  So he covered one after another
of all possible clues and finally was able to fool the rats so 
that they had too learn to go in the third door.  If he relaxed 
any of his conditions, the rats could tell.
      Now, from a scientific standpoint, that is an A-number-
one experiment. That is the experiment that makes rat-running 
experiments sensible, because it uncovers the clues that the 
rat is really using--not what you think it's using.  And that 
is the experiment that tells exactly what conditions you have 
to use in order to be careful and control everything in an 
experiment with rat-running.
      I looked into the subsequent history of this research.
The next experiment, and the one after that, never referred
to Mr. Young.  They never used any of his criteria of putting
the corridor on sand, or being very careful.  They just went
right on running rats in the same old way, and paid no
attention to the great discoveries of Mr. Young, and his papers
are not referred to, because he didn't discover anything about
the rats.  In fact, he discovered all the things you have to do
to discover something about rats.  But not paying attention to
experiments like that is a characteristic of cargo cult science.
      Another example is the ESP experiments of Mr. Rhine,
and other people.  As various people have made criticisms--
and they themselves have made criticisms of their own
experiments--they improve the techniques so that the effects
are smaller, and smaller, and smaller until they gradually
disappear.  All the parapsychologists are looking for some
experiment that can be repeated--that you can do again and
get the same effect--statistically even.  They run a million
rats--no, it's people this time--they do a lot of things and get
a certain statistical effect.  Next time they try it they don't 
get it any more.  And now you find a man saying that it is an
irrelevant demand to expect a repeatable experiment.  This is
science?
      This man also speaks about a new institution, in a talk
in which he was resigning as Director of the Institute of
Parapsychology. And, in telling people what to do next, he
says that one of the things they have to do is be sure they
only train students who have shown their ability to get PSI
results to an acceptable extent--not to waste their time on
those ambitious and interested students who get only
chance results.  It is very dangerous to have such a policy
in teaching--to teach students only how to get certain
results, rather than how to do an experiment with scientif-
ic integrity.
      So I have just one wish for you--the good luck to be
somewhere where you are free to maintain the kind of
integrity I have described, and where you do not feel forced
by a need to maintain your position in the organization, or 
financial support, or so on, to lose your integrity.  May you
have that freedom.