Jost's Law

Jost's Law (or The First Jost's Law) was proposed by Adolph Jost in 1897 and says that if two associations are of equal strength but of different age, a new repetition has a greater value for the older one.

This little known law was inspired by the work of Ebbinghaus of 12 years earlier (1885). It is a different formulation of the concept of the spacing effect. It also has deep implication as one of the earliest realizations of the existence of two components of long-term memory.

The Second Jost's Law completes the picture by stating: Given two associations of equal strength, the older will decrease less with the passage of time.

In 1966, Herbert Simon observed that exponential forgetting quarrels with the Jost's Law and predicted that some form of overlearning must occur. Today we know that this overlearning has the form of memory stability and is achieved by spaced repetition.

The two component model uses the terms stability and retrievability, Robert Bjork uses storage strength and retrieval strength, Jost used strength and age. The reference to time is interesting because retrievability is arguably best expressed as a measure of time.

Retrievability defined as probability of recall in reference to atomic memories may be counter-intuitive.

This glossary entry is used to explain "History of spaced repetition" by Piotr Wozniak (June 2018)