Cobra Effect · Learning and memory
The Feynman technique
If you cannot explain it simply, you have found a gap.
6 cards, read aloud in 2:32, with a test and sources.
Brazil, the early 1950s. The students can recite everything and use none of it.
Richard Feynman spent time teaching physics in Rio de Janeiro. His students could quote the textbook on how light behaves when it reflects off water at a certain angle. He asked them to look out at the bay and tell him what they would see. Nobody could. They had memorised the words and never met the thing.
Feynman’s own test for understanding was brutal.
A colleague once asked him to prepare a first year lecture on a deep result in quantum physics. A few days later Feynman came back and said he could not do it. He could not bring it down to a level a beginner could follow. Which meant, he said, that physicists did not really understand it yet.
That is the idea now called the Feynman technique.
Take a thing you think you know. Explain it, in plain words, on a blank page or to a patient friend, as if to a bright twelve year old. Wherever you reach for jargon, or the sentence goes vague, you have found the edge of your understanding. Go back to the source for that piece only. Then explain again.
Feynman never called it that.
The name and the four step recipe are a later popularisation, spread online decades after his death in 1988. What is documented is the habit. His biographer James Gleick describes a notebook Feynman kept as a student, titled as a record of the things he did not know. He would take a subject apart and rebuild it in his own words until it held.
It works because explaining is a test, and reading is not.
Rereading a page makes it feel familiar, and familiar feels like known. Explaining it forces every piece into the open, in order, with nothing to hide behind. The gap you find is not a failure. It is the exact place the next hour of study should go.
Tonight, pick one thing you believe you understand.
Write it out for someone who knows nothing, in words a child could follow. Read it back and circle every place you waved your hands. The circles are the syllabus. If there are none, teach it to someone and let their questions do the circling.
Sources
- Surely You’re Joking, Mr. Feynman!, Richard Feynman, 1985. The chapter on Brazil, O Americano, Outra Vez, has the students who could recite the physics and not see it in the bay. The rest is the best fun you will have with a physicist.
- Genius: The Life and Science of Richard Feynman, James Gleick, 1992. The serious biography. The notebook of things he did not know, the habit of rebuilding every subject from scratch, and the man behind the stories.
- The Feynman Learning Technique, Farnam Street. The four step version as it is usually taught today. Useful, and a good example of the later popularisation the story warns about. The method is Feynman’s. The recipe is not.
Nearby ideas
- The testing effect. Pulling an answer from memory teaches more than reading it again.
- The Dunning Kruger effect. Why the least skilled are often the worst judges of their skill.
- Desirable difficulties. The practice that feels hardest is often the practice that sticks.
- Chunking. Experts see patterns where beginners see pieces.
- Deliberate practice. Hours alone do not build skill. Focused work on weaknesses does.
- The method of loci. Pin what you need to remember to a place you already know.
- The Zeigarnik effect. Unfinished tasks stay on your mind until they are closed.
- Dual coding. Words and pictures together stick better than either alone.