We come now to the second of our four main problems, and ask how we retain, or carry around inside of us, what we have learned. The answer is, not by any process or activity. Retention is a resting state, in which a learned reaction remains until the stimulus arrives that can arouse it again. We carry around with us, not the reaction, but the machinery for making the reaction.

Consider, for example, the retention of motor skill. A boy who has learned to turn a handspring does not have to keep doing it all the time in order to retain it. He may keep himself in better form by reviewing the performance occasionally, but he retains the skill even while eating and sleeping. The same can be said of the retention of the multiplication table, or of a poem, or of knowledge of any kind. The machinery that is retained consists very largely in brain connections. Connections formed in the process of {349} learning remain behind in a resting condition till again aroused to activity by some appropriate stimulus.

But the machinery developed in the process of learning is subject to the wasting effects of time. It is subject to the law of "atrophy through disuse". Just as a muscle, brought by exercise into the pink of condition, and then left long inactive, grows weak and small, so it is with the brain connections formed in learning. With prolongation of the condition of rest, the machinery is less and less able to function, till finally all retention of a once-learned reaction may be lost.

But is anything once learned ever completely forgotten and lost? Some say no, being strongly impressed by cases of recovery of memories that were thought to be altogether gone. Childhood experiences that were supposed to be completely forgotten, and that could not at first be recalled at all, have sometimes been recovered after a long and devious search. Sometimes a hypnotized person remembers facts that he could not get at in the waking state. Persons in a fever have been known to speak a language heard in childhood, but so long disused as to be completely inaccessible in the normal state. Such facts have been generalized into the extravagant statement that nothing once known is ever forgotten. For it is an extravagant statement. It would mean that all the lessons you had ever learned could still be recited, if only the right stimulus could be found to arouse them; it would 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.

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 at first than later. More is lost in the first hour than in the second hour, and more in the first week than in the second week. Few of the experiments have been continued long enough to bring the curve actually to the zero line, but it has come very close to that line in tests conducted after an interval of two to four months.

It must be understood that this classical curve of forgetting only holds good, strictly, for material that has barely been learned. Reactions that have been drilled in thoroughly and repeatedly fall off very slowly at first, and the further course of the curve of forgetting has not been accurately followed in their case. A typist who had spent perhaps two hundred hours in drill, and then dropped typewriting for a year, recovered the lost ground in less than an hour of fresh practice, so that the retention, as measured by the saving method, was over ninety-nine per cent.

Somewhat different from the matter of the curve of forgetting is the question of the rate of forgetting, as {353} dependent on various conditions. The rate of forgetting depends, first, on the thoroughness of the learning, as we have just seen. It depends on the kind of material learned, being very much slower for meaningful than for nonsense material, though both have been learned equally well. Barely learned nonsense material is almost entirely gone by the end of four months, but stanzas of poetry, just barely learned, have shown a perceptible retention after twenty years.

Very fortunately, the principles of economy of memorizing hold good also for retention. Forgetting is slower when relationships and connections have been found in the material than when the learning has been by rote. Forgetting is slower after active recitation than when the more passive, receptive method of study has been employed. Forgetting is slower after spaced than after unspaced study, and slower after whole learning than after part learning.

An old saying has it that quick learning means quick forgetting, and that quick learners are quick forgetters. Experiment does not wholly bear this out. A lesson that is learned quickly because it is clearly understood is better retained than one which is imperfectly understood and therefore slowly learned; and a learner who learns quickly because he is on the alert for significant facts and connections retains better than a learner who is slow from lack of such alertness. The wider awake the learner, the quicker will be his learning and the slower his subsequent forgetting; so that one is often tempted to admonish a certain type of studious but easy-going person, "for goodness' sake not to dawdle over his lessons", with any idea that the more time he spends with them the longer he will remember them. More gas! High pressure gives the biggest results, provided only it is directed into high-level observation, and does not simply generate fear and worry and a rattle-brained frenzy of rote learning.{354}