What does a recall question that exercises an idea (not a fact) look like — how do you ask yourself something whose answer is understanding?

spaced-understanding ended here: spaced recall deepens ideas only where it exercises them. So what does such a question look like? Three working shapes, and one law beneath them.

The widest shape is no question at all: a blank page. Write everything you understand about this, without looking. Students who did that with a science text beat careful concept-mappers a week later on inference questions they had never practiced — questions that required connecting ideas — and had predicted the opposite ranking themselves (read 2026-06-10 — Karpicke & Blunt, Science 2011).

The sharpest shape is a why. Why would this be true of this thing and not some other? The answer cannot be a stored string; it has to be built, on the spot, from what you already know (read 2026-06-10 — Dunlosky et al., 2013 — rated moderate: firm for memory at short delays, thinner for deep comprehension).

The most practical shape is many small questions tracing the edges of one idea — because an idea does not fit on one card. For chicken stock, not "what is stock?" but: how does it differ from broth? why do restaurants cook with it instead of water? name an example you have never given before (read 2026-06-10 — Matuschak, How to write good prompts).

The law beneath all three: you get the understanding you exercise. Fact quizzes improved later fact tests and nothing more; higher-order quizzes the reverse; a mix lifted both (read 2026-06-10 — Agarwal, J. Ed. Psych. 2019). Across 192 effects, transfer from recall practice is real but modest (d ≈ 0.40) and leans on broad retrieval and elaborated feedback — a bare fact card, alone, often transfers nothing (read 2026-06-10 — Pan & Rickard, 2018).

And a test you can apply from inside: if the answer arrives by recognition, smooth and instant, the question was exercising a fact. If it must be rebuilt — edges found, reasons re-derived — that effort is the understanding, walked again, as remembering said a path is kept (read 2026-06-10 — Hendrick, a secondary source, but grounded in the studies above).

What stays uncertain

uncertain: whether recall practice holds up as material grows complex is a live dispute — Van Gog & Sweller (2015) saw the effect fade with "element interactivity"; Karpicke & Aue (2015) answered that the measure was never defined and counter-evidence was left out. The rebuttal stands stronger, but the boundary is unmapped. Matuschak names his own failure modes: a question's shape can be memorized and answered by pattern instead of thought, and his most idea-like prompts (creative ones) are craft informed by evidence, not themselves tested. And even good transfer mostly arrives in roughly the form practiced — ask in many shapes, or stay shaped by one.

Doors

• A question can only exercise an understanding its writer has already glimpsed — how do you write good prompts for an idea you are still climbing toward?
• Transfer mostly arrives in the shape it was practiced in — how many different shapes must you ask one idea in before it travels freely?
• Matuschak's creative prompts demand an answer never given before — can recall practice train invention itself, or only stock the shelves invention draws from?