The observation and description of the facts of consciousness, then, is based directly on the fact that experience, as the psychologist deals with it, possesses a focus and margin. Nature as conceived by the physical sciences presents no such distinction. The facts are what they are, and their character as focal or marginal, as clear or obscure, depends altogether upon their relation to an intelligence. Or we may say that if the facts of experience were always focal and never marginal, it would never occur to us to speak of consciousness as we do at present. As long as we confine ourselves to a given color, shape or temperature, as experienced focally, we are not dealing with consciousness, but with objects. An analysis of such facts that does not bring in the marginal is not an analysis of consciousness, but an analysis of physical reality. Even if we consider non-physical objects, such as mathematical or economic concepts, we find that our analysis is not psychological as long as the marginal is left out. The consideration of the margin, however, brings us into the presence of facts which are of a distinctive kind and which warrant a new science. Let the margin be eliminated and psychology disappears at the same time. The psychological doctrine of focus and margin, then, is a matter of fundamental importance. On the interpretation of this doctrine depend our systems of psychology and of philosophy. What, then, is meant by focus and margin? If we turn to our psychologies, we seem to be confronted once more with something that everybody knows and nobody can define. But since we have to do with a distinction, the obligation to differentiate cannot be wholly ignored. Consciousness is sometimes likened to a visual field and sometimes to the waves of the sea. Like the visual field it has a foreground and a background, a near and a remote, a center and a margin or periphery. The contents of consciousness are vivid or clear in the center of this field and fade away into vagueness or obscureness in proportion to their approach to the periphery. Or, to take the other comparison, the focus may be represented by the crest of a wave and the margin by what we may call its base. This illustration has the advantage that it indicates the difference between higher and lower degrees of concentration. As concentration increases, the crest of the wave rises higher and its width decreases, while the reverse is true where the concentration of attention is less intense. All consciousness possesses the distinction of focus and margin in some degree; however much we may be absorbed in an object or topic, there is always an indirect mental vision that informs us of other facts, which for the time being are in the background of our consciousness.