We want to know how, by its own vitality, and without carrying complementary material into a mythical unconscious, consciousness can, in course of time, modify the structure of its surroundings; how, at every moment, its former experience is present to it in the form of a horizon which it can reopen 'if it chooses to take that horizon as a theme of knowledge' in an act of recollection, but which it can equally leave on the fringe of experience, and which then immediately provides the perceived with a present atmosphere and significance.