e of muscular exercise, it is not
surprising to find it true of mental performances as well.

2. The law of _recency_ refers to the gradual weakening of the
machinery for executing a reaction when no longer exercised; it is the
general biological law of "atrophy through disuse" applied to the
special case of learned reactions. As exercise improves the linkage
between stimulus and response, so disuse allows the linkage to
deteriorate. This law is pictured more completely and quantitatively
in the curve of forgetting.

Really, there are two laws of recency, the one being a {391} law of
retention, the other a law of momentary warming up through exercise.
The law of retention, or of forgetting, is the same as atrophy through
disuse. The warming-up effect, well seen in the muscle which is
sluggish after a long rest but becomes lively and responsive after a
bit of exercise, [Footnote: See p. 73.] appears also in the fact that
a skilled act needs to be done a few times in quick succession before
it reaches its highest efficiency, and in the fact of "primary
memory", the lingering of a sensation or thought for a few moments
after the stimulus that aroused it has ceased. Primary memory is not
strictly memory, since it does not involve the recall of facts that
have dropped out of mind, but just a new emphasis on facts that have
not yet completely dropped out. Warming up is not a phenomenon of
learning, but it is a form of recency, and is responsible for the very
strong "recency value" that is sometimes a help in learning,
[Footnote: See p. 345.] and sometimes a hindrance in recall.
[Footnote: See p. 356.]

3. The law of _intensity_ simply means that vigorous exercise
strengthens a reaction more than weak exercise. This is to be
expected, but the question is, in the case of mental performances, how
to secure vigorous exercise. Well, by active recitation as compared
with passive reception, by close attention, by high level observation.
In active recitation, the memorizer strongly exercises the performance
that he is trying to master, while in reading the lesson over and over
he is giving less intense exercise to the same performance.

The Law of Effect

We come now to a law which has not so accepted a standing as the law
of exercise, and which may perhaps be another sub-law under that
general law. The "law of effect" may, however, be regarded simply as a
generalized statement of {392} the facts of learning by trial and
err