What is the Forgetting Curve?
The forgetting curve describes how memory for new material declines over time: loss is steepest in the first hours and days, then levels off. Hermann Ebbinghaus first measured it in the 1880s, and a 2015 replication confirmed the shape. Spaced review is the standard countermeasure, resetting the curve at each visit.
Ebbinghaus memorized lists of nonsense syllables and measured how much effort relearning them saved after delays from twenty minutes to a month. In his data, savings dropped steeply at first and then flattened, with roughly a third of the original learning still effective after a day and about a fifth after a month. Murre and Dros repeated the entire procedure in 2015 and reproduced the curve's shape.
The curve is not a fixed law of loss. Its steepness depends on how well the material was learned, how meaningful it is, and what happens afterward. Retrieval practice and spaced review flatten it: each successful recall slows subsequent forgetting, which is the logic spaced repetition systems are built on.
The practical reading of the curve is not that memory is hopeless but that a single exposure is a rental. Most of what you read this week will be inaccessible within days unless something, a note, a highlight resurfaced later, a self-test, gives the memory another event to consolidate around.