The Feynman technique: learn it by explaining it

What the Feynman technique is

Richard Feynman was a physicist who won the Nobel Prize in 1965 and became famous for lectures that made hard physics feel simple. He never wrote down a four-step study method himself. The technique named after him was put together later from the way he learned and taught, but its core is his: if you can't explain it simply, you don't really understand it.

As a study method it's a form of active recall. Instead of rereading a topic, you produce an explanation of it from memory. Whatever you can't explain shows up on the page, in black and white, while there's still time to fix it.

The four steps

1. Pick one concept and write its name at the top of a blank page: “How the kidney concentrates urine”, “Consideration in contract law”, “When French uses the subjunctive”.
2. Explain it in plain words, from memory, as if to a classmate who missed the lecture. No jargon unless you define it, and no peeking at your notes.
3. Find the gaps: the step you skipped, the term you used but couldn't define, the place where you wrote “and then somehow”. Go back to your slides or textbook for exactly those parts.
4. Simplify and retell: rewrite the explanation with what you fixed, add an example or an analogy, and try it again a day or two later without looking.

The beginner in step two is a test, not an audience. Explaining to someone who knows nothing stops you from hiding behind terms you've memorised but don't understand. If a word does real work in your explanation, you have to be able to say what it means.

A worked example

Say the concept is osmosis. A first attempt might read: “Osmosis is when water moves across a membrane to where there's more stuff.” It's not wrong, but it's full of gaps. What kind of membrane? What stuff? Why does the water move, and when does it stop?

Back to the textbook for those four questions, and the retold version becomes: “Osmosis is the net movement of water across a membrane that lets water through but not the particles dissolved in it. Water moves from the side with fewer dissolved particles to the side with more, which evens out the concentrations on both sides.”

Each gap you found is now a good flashcard: “In osmosis, which way does water move?” and “What kind of membrane does osmosis need?” The explanation found them, and the cards will keep them.

Why explaining works

In a 1994 study, Michelene Chi and her colleagues had students read a textbook passage about the human circulatory system. Some were prompted to explain each sentence to themselves as they read. Those students understood the system better afterwards than students who read it without explaining, and the ones who explained the most learned the most. Psychologists call this the self-explanation effect.

Teaching has a similar effect. In a 2014 study by John Nestojko and colleagues, students who expected to teach a passage to someone else recalled more of it, and more of its main points, than students who expected a test, even though nobody ended up teaching. Logan Fiorella and Richard Mayer found in 2013 that students who actually taught a lesson on video remembered it better a week later than students who only prepared to teach it.

A large 2013 review of study techniques led by John Dunlosky rated self-explanation, along with asking yourself why a fact is true, as moderately useful: it helps, with less evidence behind it than practice testing and spacing. The Feynman technique, done without notes, is both self-explanation and practice testing at once. See the study techniques, ranked by the research.

The illusion of understanding

In a 2002 study, Leonid Rozenblit and Frank Keil asked people to rate how well they understood everyday things like a zipper, a flush toilet or a cylinder lock. Then they asked them to write a step-by-step explanation of how each one works. After trying, people rated their own understanding much lower. The researchers called it the illusion of explanatory depth.

Students meet the same illusion with course material. Recognising a slide feels like knowing it, because it looks familiar. Writing the explanation is the quickest way to find out which topics you know and which you only recognise, and it's far better to find out the evening you study than in the exam hall.

Mistakes that make it less useful

• Explaining with your notes open. Then you're reading aloud, not recalling. Close them, explain, and only then check.
• Picking a whole chapter. One mechanism, one definition or one rule at a time is enough for one page.
• Skipping the check. An explanation that sounds right can still be wrong, so compare it with the source every time.
• Stopping at simple. A good exam answer is plain and precise: keep the terms your examiner expects, and define them.
• Doing it once. Explain it again from scratch a few days later to see what stuck.

When to use it, and when to use something else

The technique is at its best with ideas that have parts and causes: mechanisms in physiology, processes in chemistry, arguments in philosophy, legal tests with several elements, grammar rules with exceptions. These are the topics where students most often recognise the words but can't put them together.

It's slow for things that are simply facts: drug doses, dates, vocabulary, the branches of a nerve. For those, flashcards with spaced repetition are faster. A good routine uses both: explain to understand, then make cards so you remember. See how to make flashcards that work.

Using it with flashcards

Cards that ask why and how keep the explaining going between sessions. “Why does the loop of Henle need to be a loop?” asks for a short explanation, not a single word, and answering it is a small Feynman exercise every time it comes back.

FlashCardz can do the card-writing half for you. Add your lecture PDF, and it writes questions on the key ideas, each quoting the line it came from, so when you check an answer you see the exact sentence in your own material. The cards you miss come back the next night from a new angle, such as asking you to explain or apply the idea. Turn a PDF into flashcards.