When we have thus chosen suitable subjects, observation shows from the start sufficiently distinct varieties, different orientations of the imagination depending on intellectual causes, such as the predominance of visual or acoustic or tactile-motor images making for mechanical invention; or dependent on emotional causes, that is, of character, according as the latter is timid, joyous, exuberant, retired, healthy, sickly, etc. If we now attempt to follow the development of the child-imagination, we may distinguish four principal stages, without assigning them, otherwise, a rigorous chronological order. 1. The first stage consists of the passage from passive to creative imagination. Its history would be long were we to include all the hybrid forms that are made up partly of memories, partly of new groupings, being at the same time repetition and construction. Even in the adult, they are very frequent. I know a person who is always afraid of being smothered, and for this reason urgently asks that in his coffin his shirt be not tight at the neck: this odd prepossession of the mind belongs neither to memory nor to imagination. This particular case illustrates in a very clear form the nature of the first flights of the mind attempting to exercise its imaginative powers. Without enumerating other facts of this kind, it is more desirable to follow the imagination's development, limiting ourselves to two forms of the psychic life--perception and illusion. The necessary presence of the image in these two forms has been so often proven by contemporary psychology that a few words to recall this to mind will be sufficient. There seems to be a radical difference between perception, which seizes reality, and imagination. Nevertheless, it is generally admitted that in order to rise above sensation to perception, there must be a synthesis of images. To put it more simply, two elements are required--one, coming from without, the physiological stimulus acting on the nerves and the sensory centers, which becomes translated in consciousness through the vague state that goes by the name "sensation"; the other, coming from within, adds to the sensations present appropriate images, remnants of former experiences. So that perception requires an apprenticeship; we must feel, then imperfectly perceive, in order to finally perceive well. The sensory datum is only a fraction of the total fact; and in the operation we call "perceiving," that is, apprehending an object directly, a part only of the object is represented.