In order to thoroughly comprehend the absolute necessity for dissociation, let us note that total redintegration is _per se_ a hindrance to creation. Examples are given of people who can easily remember twenty or thirty pages of a book, but if they want a particular passage they are unable to pick it out--they must begin at the beginning and continue down to the required place. Excessive ease of retention thus becomes a serious inconvenience. Besides these rare cases, we know that ignorant people, those intellectually limited, give the same invariable story of every occurrence, in which all the parts--the important and the accessory, the useful and the useless--are on a dead level. They omit no detail, they cannot select. Minds of this kind are inapt at invention. In short, we may say that there are two kinds of memory: one is completely systematized, e.g., habits, routine, poetry or prose learned by heart, faultless musical rendering, etc. The acquisition forms a compact whole and cannot enter into new combinations. The other is not systematized; it is composed of small, more or less coherent groups. This kind of memory is plastic and capable of becoming combined in new ways. We have enumerated the spontaneous, natural causes of association, omitting the voluntary and artificial causes, which are but their imitations. As a result of these various causes, images are taken to pieces, shattered, broken up, but made all the readier as materials for the inventor. This is a process analogous to that which, in geologic time, produces new strata through the wearing away of old rocks. II Association is one of the big questions of psychology; but as it does not especially concern our subject, it will be discussed in strict proportion to its use here. Nothing is easier than limiting ourselves. Our task is reducible to a very clear and very brief question: What are the forms of association that give rise to new combinations and under what influences do they arise? All other forms of association, those that are only repetitions, should be eliminated. Consequently, this subject can not be treated in one single effort; it must be studied, in turn, in its relations to our three factors--intellectual, emotional, unconscious. It is generally admitted that the expression "association of ideas" is faulty.[8] It is not comprehensive enough, association being active also in psychic states other than ideas. It seems indicative rather of mere juxtaposition, whereas associated states modify one another by the very fact of their being connected. But, as it has been confirmed by long usage, it would be difficult to eliminate the phrase.