In many animals that are endowed only with memory the return of images is always provoked. Sensation from without or from within bring them into consciousness under the form, pure and simple, of former experience; whence we have reproduction, repetition without new associations. People of slight imagination and used to routine approach this mental condition. But, as a matter of fact, man from his second year on, and some higher animals, go beyond this stage--they are capable of spontaneous revival. By this term I mean that revival that comes about abruptly, without _apparent_ antecedents. We know that these act in a latent form, and consist of thinking by analogy, affective dispositions, unconscious elaboration. This sudden appearance excites other states which, grouped into new associations, contain the first elements of the creative act. Taken altogether, and however numerous its manifestations, the constructive imagination seems to me reducible to three forms, which I shall call _sketched_, _fixed_, _objectified_, according as it remains an internal fancy, or takes on a material but contingent and unstable form, or is subjected to the conditions of a rigorous internal or external determinism. (a) The _sketched_ form is primordial, original, the simplest of all; it is a nascent moment or first attempt. It appears first of all in dreaming--an embryonic, unstable and uncoordinated manifestation of the creative imagination--a transition-stage between passive reproduction and organized construction. A step higher is revery, whose flitting images, associated by chance, without personal intervention, are nevertheless vivid enough to exclude from consciousness every impression of the external world--so much so that the day-dreamer re-enters it only with a shock of surprise. More coherent are the imaginary constructions known as "castles in Spain"--the works of a wish considered unrealizable, fancies of love, ambition, power and wealth, the goal of which seems to be forever beyond our reach. Lastly, still higher, come all the plans for the future conceived vaguely and as barely possible--foreseeing the end of a sickness, of a business enterprise, of a political event, etc. This vague and "outline" imagination, penetrating our entire life, has its peculiar characters--the unifying principle is _nil_ or ephemeral, which fact always reduces it to the dream as a type; it does not externalize itself, does not change into acts, a consequence of its basically chimerical nature or of weakness of will, which reduces it to a strictly internal and individual existence. It is needless to say that this kind of imagination is a permanent and definite form with the dreamers living in a world of ceaselessly reappearing images, having no power to organize them, to change them into a work of art, a theory, or a useful invention.