Man is able to create for two principal reasons. The first, motor in nature, is found in the action of his needs, appetites, tendencies, desires. The second is the possibility of a spontaneous revival of images that become grouped in new combination. 1. We have already shown in detail[146] that the hypothesis of a "creative instinct," if the expression is used not as an abbreviated or metaphorical formula but in the strict sense, is a pure chimera, an empty entity. In studying the various types of imagination we have always been careful to note that every mode of creation may be reduced, as regards its beginnings, to a tendency, a want, a special, determinate desire. Let us recall for the last time these initial conditions of all invention--these desires, conscious or not, that excite it. The wants, tendencies, desires--it matters not which term we adopt--the whole of which constitutes the instinct of individual preservation, have been the generators of all inventions dealing with food-getting, housing, making of weapons, instruments, and machines. The need for individual and social expansion or extension has given rise to military, commercial, and industrial invention, and in its disinterested form, esthetic creation. As for the sexual instinct, its psychic fertility is in no way less than the physical--it is an inexhaustible source of imagination in everyday life as well as in art. The wants of man in contact with his fellows have engendered, through instinctive or reflective action, the numerous social and practical creations regulating human groups, and they are rough or complex, stable or unstable, just or unjust, kindly or harsh. The need of knowing and of explaining, well or ill, has created myths, religions, philosophical systems, scientific hypotheses. Every want, tendency or desire may, then, become creative, by itself or associated with others, and into these final elements it is that analysis must resolve "creative spontaneity." This vague expression corresponds to a _sum_, not to a special property.[147] Every invention, then, has a _motor_ origin; _the ultimate basis of the constructive imagination is motor_. 2. But needs and desires by themselves cannot create--they are only a stimulus and a spring. Whence arises the need of a second condition--the spontaneous revival of images.