Just as repetition or exercise tends to fix a fact in memory, so disuse of a connection results in the fact fading from memory.  “Forgetting” is a matter of everyday experience for every one.  The rate of forgetting has been the subject of experimental work.  Ebbinghaus’s investigation is the historical one.  The results from this particular series of experiments are as follows:  During the first hour after study over half of what was learned had been forgotten; at the end of the first day two thirds, and at the end of a month about four fifths.  These results have been accepted as capable of rather general application until within the last few years.  Recent experiments in learning poetry, translation of French into English, practice in addition and multiplication, learning to toss balls and to typewrite, and others, make clear that there is no general curve of forgetting.  The rate of forgetting is more rapid soon after the practice period than later, but the total amount forgotten and the rate of deterioration depend upon the particular function tested.  No one function can serve as a sample for others.  No one curve of forgetting exists for different functions at the same stage of advancement or for the same function at different stages of advancement in the same individual, much less for different functions, at different stages of advancement, in different individuals.  Much more experimental work is needed before definite general results can be stated.

This experimental work, however, is suggestive along several lines, (1) It seems possible that habits of skill, involving direct sensori-motor bonds, are more permanent than memories involving connections between association bonds.  In other words, that physical habits are more lasting than memories of intellectual facts. (2) Overlearning seems a necessary correlate of permanence of connection.  That is, what seems to be overlearning at beginning stages is really only raising the material to the necessary level above the threshold for retention.  How far overlearning is necessary and when it becomes wasteful are yet to be determined. (3) Deterioration is hastened by competing connections.  If during the time a particular function is lying idle other bonds of connection are being formed into some parts or elements of it, the rate of forgetting of the function in question is hastened and the possibility of recall made more problematic.  The less the interference, the greater will be the permanence of the particular bonds.

A belief maintained by some psychologists is in direct opposition to this general law that disuse causes deterioration.  It is usually stated something like this, that periods of incubation are necessary in acquiring skill, or that letting a function lie fallow results in greater skill at the end of that period, or briefly one learns to skate in summer and swim in winter.  To some extent this is true, but as stated it is misleading.  The general law of