Spaced repetition memory prompts should usually focus on one atomic unit

If you’ve just learned a new way to cook peas, you might write a prompt for a Spaced repetition memory system like: “Q. How do I cook peas sous vide?” “A. 18m @ 70°C”. But I find that questions like this are usually a struggle—I’ll frequently forget the answer. Questions which draw on multiple independent ideas seem to trip over this problem.

Note, however, that the research literature on broader applications of the Testing effect paints a more ambivalent picture: How complex should tasks be for test-enhanced learning?

Why is it important that questions focus on one idea? Michael Nielsen (2018) suggests:

I suspect it’s partly about focus. When I made mistakes with the combined question, I was often a little fuzzy about where exactly my mistake was. That meant I didn’t focus sharply enough on the mistake, and so didn’t learn as much from my failure. When I fail with the atomic questions my mind knows exactly where to focus.

What constitutes “one idea”? That depends on your prior context; “one idea” seems to consist of one step on top of whatever knowledge you’ve already deeply internalized. Another way to look at that might be relative to “Chunks” in human cognition: a single idea is expressed in one “chunk,” whatever that might mean for you.

The fix in such instances is simple: break the question down into multiple simpler questions. Then, perhaps, add another question which integrates those two simpler questions. (This seems like an opportunity for Spaced repetition and knowledge modeling). The process of writing questions which focus precisely on one idea does seem to help sharpen my focus on the key elements of a topic (one angle on Writing one’s own spaced repetition prompts seems to promote understanding).

Wozniak (1999) supplies a good example (also demonstrating Spaced repetition memory prompts should be concise):

Ill-formulated knowledge - Complex and wordy
Q: What are the characteristics of the Dead Sea?
A: Salt lake located on the border between Israel and Jordan. Its shoreline is the lowest point on the Earth’s surface, averaging 396 m below sea level. It is 74 km long. It is seven times as salty (30% by volume) as the ocean. Its density keeps swimmers afloat. Only simple organisms can live in its saline waters
Well-formulated knowledge - Simple and specific
Q: Where is the Dead Sea located?
A: on the border between Israel and Jordan
Q: What is the lowest point on the Earth’s surface?
A: The Dead Sea shoreline
Q: What is the average level on which the Dead Sea is located?
A: 400 meters (below sea level)
Q: How long is the Dead Sea?
A: 70 km
Q: How much saltier is the Dead Sea than the oceans?
A: 7 times
Q: What is the volume content of salt in the Dead Sea?
A: 30%
Q: Why can the Dead Sea keep swimmers afloat?
A: due to high salt content
Q: Why is the Dead Sea called Dead?
A: because only simple organisms can live in it
Q: Why only simple organisms can live in the Dead Sea?
A: because of high salt content

Q. SRS prompts should usually focus on one atomic unit. How is “one atomic unit” defined?
A. Depends on the complexity of your prior knowledge. One idea is a simple combination of chunks you’ve already encoded.

Q. Why does MN think SRS prompts focused on more than one idea don’t work well?
A. When making a mistake with a combined question, it’s harder to focus sharply on exactly where the mistake was.


Nielsen, M. (2018). Augmenting Long-term Memory.

Piotr Wozniak - Effective learning - Twenty rules of formulating knowledge