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The Feynman Technique for not Fooling Yourself

Richard Feynman (1918 – 1988) was an American, Nobel Prize-winning physicist, who besides being a celebrated scientist—in 1999, he was ranked as one of the ten greatest physicists of all time by Physics World journal and he was involved in the development of the atomic bomb during World War II—was also called The Great Explainer because of his ability to present complex ideas in simple, graspable ways. As a testament to this, Feynman usually advocates for the idea that an individual ensure he understands a concept deeply, sincerely and not fool themselves.

In a 1974 commencement address he gave at the California Institute of Technology, Richard Feynman discusses what he called the Cargo Cult Science, a practise involving the use of mere manipulations of a system, albeit devoid of any real knowledge of how the system works, with the expectation of getting the exact, trustworthy results that the original system would give.

This method of doing things, Feynman elaborates, is characteristics of a group of people whom Feynman referred to as the Cargo Cult.

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 essential, because the planes don’t land.

Like the Cargo Cult people, many of us brag about knowing many things but our knowledge is only superficial and flimsy. This usually happens when we build our knowledge on other people’s words, opinions or knowledge, like Montaigne wrote:

We take other men’s knowledge and opinions upon trust; which is an idle and superficial learning. We must make them our own. We are just like a man who, needing fire, went to a neighbour’s house to fetch it, and finding a very good one there, sat down to warm himself without remembering to carry any back home. What good does it do us to have our belly full of meat if it is not digested, if it is not transformed into us, if it does not nourish and support us?

We would move a great distance higher on the intellectual ladder if we take steps to move from the level of merely knowing to the level of deeply understanding. In a short video clip referenced by Farnam Street’s Shane Parish, we see Feynman differentiating at length between knowing something—that is knowing some of its properties like its name, colour etc—and understanding it beyond what its properties can tell:

See that bird? It’s a brown-throated thrush, but in Germany it’s called a halzenfugel, and in Chinese they call it a chung ling and even if you know all those names for it, you still know nothing about the bird. You only know something about people; what they call the bird. Now, that thrush sings, and teaches its young to fly, and flies so many miles away during the summer across the country, and nobody knows how it finds its way.


In order to talk to each other, we have to have words, and that’s all right. It’s a good idea to try to see the difference, and it’s a good idea to know when we are teaching the tools of science, such as words, and when we are teaching science itself.


There is a first grade science book which, in the first lesson of the first grade, begins in an unfortunate manner to teach science, because it starts off with the wrong idea of what science is. There is a picture of a dog–a windable toy dog–and a hand comes to the winder, and then the dog is able to move. Under the last picture, it says “What makes it move?” Later on, there is a picture of a real dog and the question, “What makes it move?” Then there is a picture of a motorbike and the question, “What makes it move?” and so on.

I thought at first they were getting ready to tell what science was going to be about–physics, biology, chemistry–but that wasn’t it. The answer was in the teacher’s edition of the book: the answer I was trying to learn is that “energy makes it move.”

Now, energy is a very subtle concept. It is very, very difficult to get right. What I mean is that it is not easy to understand energy well enough to use it right, so that you can deduce something correctly using the energy idea–it is beyond the first grade. It would be equally well to say that “God makes it move,” or “spirit makes it move,” or “movability makes it move.” (In fact, one could equally well say “energy makes it stop.”)

Look at it this way: that’s only the definition of energy; it should be reversed. We might say when something can move that it has energy in it, but not what makes it move is energy. This is a very subtle difference. It’s the same with this inertia proposition.

Perhaps I can make the difference a little clearer this way: If you ask a child what makes the toy dog move, you should think about what an ordinary human being would answer. The answer is that you wound up the spring; it tries to unwind and pushes the gear around.

What a good way to begin a science course! Take apart the toy; see how it works. See the cleverness of the gears; see the ratchets. Learn something about the toy, the way the toy is put together, the ingenuity of people devising the ratchets and other things. That’s good. The question is fine. The answer is a little unfortunate, because what they were trying to do is teach a definition of what is energy. But nothing whatever is learned.


I think for lesson number one, to learn a mystic formula for answering questions is very bad.

Now, this brings us to The Feynman Technique. A mental model for understanding any concept (either in physics, mathematics or philosophy) deeply and not just wander around with the mystic formula or crammed knowledge of such concept.

The layout of the Feynman Technique was not expressly presented by Richard Feynman himself but useful crumbs of the concept were scattered all over many of his works. For example, in the earlier referenced Cargo Cult Science, he had said, “The first principle is that you must not fool yourself, and you are the easiest person to fool.” That is, do not conclude or profess to understand something when in reality you’ve not. “Never say that you’ll give a talk,” Feynman admonished, “unless you know clearly what you’re going to talk about and more or less what you’re going to say”.

I guess one of the closest we can get to Feynman explaining the Feynman Technique is in the video clip referenced earlier where Feynman later suggested:

Test it this way: you say, “Without using the new word which you have just learned, try to rephrase what you have just learned in your own language.” Without using the word “energy,” tell me what you know now about the dog’s motion.” You cannot. So you learned nothing about science. That may be all right. You may not want to learn something about science right away. You have to learn definitions. But for the very first lesson, is that not possibly destructive?

The Feynman Technique has however been articulated into an easy-to-follow 4-step process thus:

  1. Write down and read about the concept you want to learn
  2. Teach/explain the concept in your own terms
  3. If your explanation feels shaky, go back to the books
  4. Rewrite in simpler terms or use analogies

This process works either for understanding a new concept in any discipline, or for testing your previous understanding of the concept. Below are some third-party articles rendering more insights on this technique.

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