On the other hand, psychologists are not at all agreed as regards the determination of the principal laws or forms of association. Without taking sides in the debate, I adopt the most generally accepted classification, the one most suitable for our subject--the one that reduces everything to the two fundamental laws of contiguity and resemblance. In recent years various attempts have been made to reduce these two laws to one, some reducing resemblance to contiguity; others, contiguity to resemblance. Putting aside the ground of this discussion, which seems to me very useless, and which perhaps is due to excessive zeal for unity, we must nevertheless recognize that this discussion is not without interest for the study of the creative imagination, because it has well shown that each of the two fundamental laws has a characteristic mechanism. Association by contiguity (or continuity), which Wundt calls external, is simple and homogeneous. It reproduces the order and connection of things; it reduces itself to habits contracted by our nervous system. Is association by resemblance, which Wundt calls internal, strictly speaking, an elementary law? Many doubt it. Without entering into the long and frequently confused discussions to which this subject has given rise, we may sum up their results as follows: In so-called association by resemblance it is necessary to distinguish three moments--(a) That of the presentation; a state _A_ is given in perception or association-by-contiguity, and forms the starting point. (b) That of the work of assimilation; _A_ is recognized as more or less like a state _a_ previously experienced. (c) As a consequence of the coexistence of _A_ and _a_ in consciousness, they can later be recalled reciprocally, although the two original occurrences _A_ and _a_ have previously never existed together, and sometimes, indeed, may not possibly have existed together. It is evident that the crucial moment is the second, and that it consists of an act of active assimilation. Thus James maintains that "it is a relation that the mind perceives after the fact, just as it may perceive the relations of superiority, of distance, of causality, of container and content, of substance and accident, or of contrast between an object, and some second object which the associative machinery calls up."[9] Association by resemblance presupposes a joint labor of association and dissociation--it is an active form. Consequently it is the principal source of the material of the creative imagination, as the sequel of this work will sufficiently show.