Main idea

A spaced repetition system — one box every three days, one every fortnight, one every two months, a card moving boxes when it seems known — organizes the occasions for rereading. It says nothing about what you do during the rereading, and that is where everything is decided.

Checking that you can recite a card teaches one thing only: that it is memorized. The useful operation is another. It consists in putting the formulation up against what has happened since the last exposure: has an experience confirmed it, has a conversation shifted it, has a new source qualified it, has a concrete situation weakened it?

Time does not test ideas by its duration alone. It tests them because it brings experiences, contradictions and new sources — and it only brings them to the card if the rereading arranges the encounter. A card that holds is reinforced, a card that moves is refined, a card that no longer holds goes out.

Why it matters

It changes what a successful review is. Success is not knowing the card, it is having something to set against it — and a review that never produces an adjustment signals a ritual rather than a test.

It also explains why the box mechanism is secondary: it sets the frequency of the encounters, not their content.

Nuances and limits

Not every period brings material. Between two close exposures, sometimes nothing has happened that concerns the card, and forcing the confrontation would manufacture an artificial verdict.

And the rereading judges with the eyes of the moment: a conviction can be weakened by a bad week as much as by a fact.

Open questions

• Should you keep a trace of a card's successive shifts, or does the latest formulation suffice?