ld
mean that all the lectures you ever heard (and attended to) are still
retained, that all the stories you ever read are still retained, that
all the faces you ever noticed are still retained, that all the scenes
and happenings that ever got your attention could still be revived if
only the right means were taken to revive them. There is no evidence
for any such extreme view.

The modern, scientific study of this matter began with {350}
recognizing the fact that there are _degrees of retention_, ranging
all the way from one hundred per cent, to zero, and with the invention
of methods of measuring retention. Suppose you have memorized a list
of twenty numbers some time ago, and kept a record of the time you
then took to learn it; since when you have not thought of it again.

[Illustration: Fig. 53.--(From Ebbinghaus.) The curve of forgetting.
The curve sinks at first rapidly, and then slowly, from the 100 per
cent line towards the zero line, 100 per cent. here meaning perfect
retention, and 0 no retention.]

On attempting now to recite it, you make no headway and are inclined
to think you have entirely forgotten it. But, finding the list again,
you _relearn_ it, and probably find that your time for relearning is
less than the original learning time--unless the lapse of time has run
into months. Now consider--if no time at all were needed for
relearning, because the list could be recited easily without, your
retention would be one hundred per cent. If, on the contrary, it took
you just as long now to relearn as it did originally to learn, the
retention would be zero. If it takes you now two-thirds as long to
relearn as it originally took to learn, then {351} one-third of the
work originally done on the list does not have to be done over, and
_this saving is the measure of retention_.

By the use of this method, the curve of retention, or curve of
forgetting, as it is also called, has been determined. It is a curve
that first goes down steeply, and then more and more gradually, till
it approximates to zero; which means that the loss of what has been
learned proceeds rapidly at first and then more and more slowly.

The curve of forgetting can be determined by other methods besides the
saving method--by the recall method or by the recognition method; and
data obtained by these methods are given in the adjoining tables. It
will be seen that the different methods agree in showing a curve that
falls off more rapidly