Association by contrast is, from its very nature, vague, arbitrary, indeterminate. It rests, in truth, on an essentially subjective and fleeting conception, that of contrariety, which it is almost impossible to delimit scientifically; for, most often, contraries exist only by and for us. We know that this form of association is not primary and irreducible. It is brought down by some to contiguity, by most others to resemblance. These two views do not seem to me irreconcilable. In association by contrast we may distinguish two layers,--the one, superficial, consists of contiguity: all of us have in memory associated couples, such as large-small, rich-poor, high-low, right-left, etc., which result from repetition and habit; the other, deep, is resemblance; _contrast exists only where a common measure between two terms is possible_. As Wundt remarks, a wedding may be compared to a burial (the union and separation of a couple), but not to a toothache. There is contrast between two colors, contrast between sounds, but not between a sound and a color, at least in that there may not be a common basis to which we may relate them, as in the previously given instances of "colored" sound. In association by contrast, there are conscious elements opposed to one another, and below, an unconscious element, resemblance,--not clearly and logically perceived, but felt--that evokes and relates the conscious elements. Whether this explanation be right or not, let us remark that association by contrast could not be left out, because its mechanism, full of unforeseen possibilities, lends itself easily to novel relations. Otherwise, I do not at all claim that it is entirely dependent upon the emotional factor. But, as Hoeffding observes,[16] the special property of the emotional life is moving among contraries; it is altogether determined by the great opposition between pleasure and pain. Thus, the effects of contrasts are much stronger than in the realm of sensation. This form of association predominates in esthetic and mythic creation, that is to say, in creation of the free fancy; it becomes dimmed in the precise forms of practical, mechanical, and scientific invention. III Hitherto we have considered the emotional factor under a single aspect only--the purely emotional--that which is manifested in consciousness under an agreeable or disagreeable or mixed form. But thoughts, feelings, and emotions include elements that are deeper--motor, i.e., impulsive or inhibitory--which we may neglect the less since it is in movements that we seek the origin of the creative imagination. This motor element is what current speech and often even psychological treatises designate under the terms "creative instinct," "inventive instinct;" what we express in another form when we say that creators are guided by instinct and "are pushed like animals toward the accomplishment of certain acts."