The Feynman technique: explain it simply to find what you don't know

Try it: explain something simply

Pick something you think you understand and explain it below, from memory, in a few sentences. The checker highlights the places where you might be hiding behind words. Nothing you type leaves your browser.

The checker can only see words. It can tell you that a sentence is long or that "mechanism" is doing a lot of work. It can't tell you whether your explanation is right. That part is step 4.

The four steps, worked through

Here is the technique on one concept most adults have heard of and fewer can explain: compound interest.

1. Pick a concept. Write its name at the top of a blank page. Choose something you think you already understand. That is where the gaps hide, because nothing has ever made you check.
2. Explain it simply, from memory. Write it out as if for a curious 12-year-old: short sentences, everyday words, at least one concrete example. Don't open your notes. The point is to see what is in your head, not in the book.
3. Find the gaps. Read it back. Mark every place where you got stuck, used a term you couldn't define, or jumped from one step to the next without saying why. Those are the parts you don't understand yet.
4. Go back to the source, then simplify again. Look up only the gaps. Close the source and rewrite the explanation, plainer than before. Repeat until you can explain the whole thing without reaching for jargon.

A first draft often looks like this. It is what the checker's example button fills in:

Nothing in it is wrong. But read it as a 12-year-old would, and two real gaps show up behind the highlighted words:

• "Exponential growth." This names the effect without explaining it. Why would money grow faster over time if the rate stays the same?
• "The frequency of compounding impacts the effective annual rate." Try to say this in plain words. If you can't, you have memorized the sentence, not the idea.

The other highlights are mostly style. "Basically" and "essentially" can go. "Principal" just means the money you started with. Back to the source for the two real gaps, then a second draft:

Draft 2 is longer, and that's fine. Simple doesn't mean short. It means every step is there, in words anyone can follow. The real test is not the grade level but whether you can now answer a question you couldn't before: why does the same 5% earn $50 the first year and $52.50 the second?

Where it comes from, and what Feynman actually did

Richard Feynman (1918–1988) was a physicist who shared the 1965 Nobel Prize in Physics and was famous as a teacher. He never wrote down a "Feynman technique". I couldn't find the phrase, or a four-step method, in anything he wrote or said.

The name comes from the writer Scott Young. In 2011, he released a video and transcript called "Never Forget an Idea Again with The Feynman Technique" as part of a study course. His four steps: choose a concept and write it at the top of a page; explain it as if teaching a new student; whenever you get stuck, go back to the book; and simplify the language or find an analogy wherever the explanation gets wordy. He later called it "the most popular piece of studying advice I've ever come up with" and said it is "only loosely based on Richard Feynman's practices."

In April 2012, the blog Farnam Street published its own four-step version, which it has updated since. Its current steps include "teach it to a 12-year-old", a phrasing many pages repeat today.

So the method is a modern study recipe. But the habits it borrows from are real and well documented:

• He made up examples. In Surely You're Joking, Mr. Feynman! (1985) he describes how he followed mathematicians' proofs: "I had a scheme, which I still use today when somebody is explaining something that I'm trying to understand: I keep making up examples." As they listed the conditions of a theorem, he pictured a concrete object that met them and checked whether the conclusion held.
• He listed what he didn't know. James Gleick's biography Genius (1992) describes how, preparing for his oral exams as a graduate student at Princeton, Feynman opened a fresh notebook titled "Notebook of Things I Don't Know About" and spent weeks taking apart each branch of physics he knew.
• He tested understanding by simplifying. His Caltech colleague David Goodstein once asked him why particles with spin ½ obey Fermi-Dirac statistics. Feynman offered to prepare a freshman lecture on it. A few days later he came back: "I couldn't do it. I couldn't reduce it to the freshman level. That means we really don't understand it."
• He separated names from knowledge. In What Do You Care What Other People Think? (1988), he recalls his father showing him a bird and saying that knowing its name in every language tells you nothing about the bird. "I learned very early the difference between knowing the name of something and knowing something."

One more line often linked to the technique was on his blackboard at Caltech when he died in 1988: "What I cannot create, I do not understand."

Why explaining works

I couldn't find a controlled study of the four-step Feynman technique as a package. The evidence is for its parts, and it is good.

We think we understand more than we do. In 2002, Leonid Rozenblit and Frank Keil asked university students to rate, on a 1 to 7 scale, how well they understood everyday devices like a zipper, a flush toilet, a speedometer and a sewing machine. Then they asked them to write a step-by-step explanation of how each one works, and to rate their understanding again. The ratings dropped, and several participants said they were surprised by how little they knew. Rozenblit and Keil called this the illusion of explanatory depth, and found it was much stronger for explanations of how things work than for facts, procedures or stories. Trying to explain is what breaks the illusion. That is steps 2 and 3 of the technique.

Explaining to yourself helps you learn. In a 1994 study by Michelene Chi and colleagues, eighth graders read a textbook passage on the human circulatory system. Students who were prompted to explain each line to themselves did better on a test of understanding afterward than students who read the passage twice. A 2018 meta-analysis led by Kiran Bisra pooled 69 effects from 64 research reports on self-explanation and found a moderate average benefit. A 2013 review of study techniques by John Dunlosky and colleagues rated self-explanation as moderately useful: below practice testing and spaced practice, above rereading and highlighting.

What you produce yourself sticks better. In 1978, Norman Slamecka and Peter Graf showed that people remember words they generated from a clue better than the same words they simply read. This is the generation effect. An explanation in your own words is generated, not copied. It is also a form of active recall if you write it from memory.

Limits and common mistakes

• Explaining with the book open. Then you are rephrasing, not explaining. Write from memory first, and only open the source for step 4.
• Simple but wrong. A clear explanation can still be false, and a readability score can't tell. Always check your final draft against a good source.
• Simplifying until it's no longer true. Some ideas need a precise term. Use it, but define it in plain words the first time. The goal is simple words, not missing steps.
• Picking something too big. "Economics" or "the immune system" won't fit on one page. Pick one idea: "why prices rise when the money supply grows", "what a vaccine teaches the immune system".
• No examples. Feynman's own habit was the concrete example. An explanation with no example is usually a definition.
• Doing it once. Fixing the gaps today helps you understand. Remembering it next month takes a few more rounds of recall, spread out over time. See the forgetting curve for why.
• Using it for things that don't need understanding. Vocabulary, dates and formulas you just need to recall are better served by plain flashcards.

How to use it with books and courses

You don't need to do this for every page. Use it on the few ideas that matter.

1. One idea per chapter. After each chapter of a nonfiction book, pick the one idea you most want to keep. Close the book and explain it on half a page. Our guide on how to remember what you read has more on choosing what to keep.
2. The hardest idea per lecture. After a class or a course video, explain the part that confused you most. The gaps you find are exactly what to bring to office hours, a study group or the course forum.
3. Turn gaps into questions. Every gap you found is a question you couldn't answer, like "why does the same 5% earn more each year?" Write it down. Answering it from memory next week is active recall.
4. Explain it again, later. A few days later, explain the same idea without looking at your last draft. Then again in a week or two. That is spaced repetition, and it is what turns understanding into memory.

If you want to see how these ideas fit together, Make It Stick by Brown, Roediger and McDaniel covers elaboration and the illusion of knowing in depth. Our Make It Stick quiz tests you on its key ideas.

Where Prismo fits

I built Prismo around the same first move as the Feynman technique: you write, or dictate, a few lines about what you learned, in your own words. Prismo turns that into notes and quiz questions, then brings them back on a spaced schedule, with longer gaps each time.

It doesn't replace steps 3 and 4. It won't tell you where your understanding has gaps, and it can't check your explanation against the book. Use the technique to understand an idea, and Prismo, or a notebook and a calendar, to keep it.

Sources

• Young, S. H. (2011). Never forget an idea again with the Feynman Technique (transcript, August 2011) and Learn faster with the Feynman Technique (September 1, 2011).
• Young, S. H. (2024). 5 keys to get the most out of the Feynman Technique.
• Farnam Street. The Feynman Technique. First published April 26, 2012.
• Feynman, R. P. (1985). Surely You're Joking, Mr. Feynman! Adventures of a Curious Character. W. W. Norton.
• Feynman, R. P. (1988). What Do You Care What Other People Think? Further Adventures of a Curious Character. W. W. Norton.
• Gleick, J. (1992). Genius: The Life and Science of Richard Feynman. Pantheon.
• Goodstein, D. L. (1989). Richard P. Feynman, teacher. Physics Today, 42(2), 70–75. Excerpted in Feynman at 100, Caltech Magazine, 2018.
• Rozenblit, L., & Keil, F. (2002). The misunderstood limits of folk science: An illusion of explanatory depth. Cognitive Science, 26(5), 521–562.
• Chi, M. T. H., de Leeuw, N., Chiu, M.-H., & LaVancher, C. (1994). Eliciting self-explanations improves understanding. Cognitive Science, 18(3), 439–477.
• Bisra, K., Liu, Q., Nesbit, J. C., Salimi, F., & Winne, P. H. (2018). Inducing self-explanation: A meta-analysis. Educational Psychology Review, 30(3), 703–725.
• Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving students' learning with effective learning techniques. Psychological Science in the Public Interest, 14(1), 4–58.
• Slamecka, N. J., & Graf, P. (1978). The generation effect: Delineation of a phenomenon. Journal of Experimental Psychology: Human Learning and Memory, 4(6), 592–604.
• Kincaid, J. P., Fishburne, R. P., Rogers, R. L., & Chissom, B. S. (1975). Derivation of new readability formulas for Navy enlisted personnel. Naval Technical Training Command. The source of the grade-level formula the checker uses.