The third factor upon which goodness in memory depends is the organization of associates. Number of connections is an aid to memory--but systematization among these connections is an added help. Logical arrangement of facts in memory, classification according to various principles, orderly grouping of things that belong together, make the operation of memory more efficient and economical. The difference between mere number of associations and orderly arrangement of those associations may be illustrated by the difference in efficiency between the housekeeper who starts more or less blindly to look all over the house for a lost article, and the one who at least knows that it must be in a certain room and probably in a certain bureau drawer. Although memory as a whole cannot be improved because of the limiting power of native retentiveness, memory for any fact or in any definite field may be improved by emphasizing these two factors: number of associations and organization among associations. Although all three factors are operative in securing the best type of memory, still the efficiency of a given memory may be due more to the unusual power of one of them than to the combined effect of the three. It is this difference in the functioning of these three factors which is primarily responsible for certain types of memory which will be discussed later. It must also be borne in mind that the power of these factors to operate in determining recall varies somewhat with age. Little children and old people are more dependent upon mere retentiveness than upon either of the others, the former because of lack of experience and lack of habits of thought, the latter because of the loss of both of these factors. The adult depends more on the organization of his material, while in the years between the number of the clews is probably the controlling factor. Here again there is no sharp line of division; all three are needed. So in the primary grades we begin to require children to organize, and as adults we do all we can to make the power of retention operate at its maximum. Many methods of memorizing have been used by both children and adults. Recently experimental psychology has been testing some of them. So far as the learner is concerned, he may use repetition, or concentration, or recall as a primary method. Repetition means simply the going over and over again the material to be learned--the element depended upon being the number of times the connection is made. Concentration means going over the material with attention. Not the number of connections is important, but the intensity of those connections. In recall the emphasis is laid upon reinstating the desired connections from within. In using this method, for instance, the learner goes over the material as many times as he sees necessary, then closes the book and recalls from memory what he can of it.