In the study and formulation of psychological phenomena there is one common tendency and danger, and that is of making the phenomena too schematic and sharply defined, as if we were dealing with material objects. Mental processes are not only plastic but shifting, varying, unstable, and undergo modifications of structure almost from moment to moment. We describe a complex schematically as if it had a fixed, immutable, and well-defined structure. This is far from being the case. Although there may be a fairly fixed nucleus, the cluster, as a whole, is ill defined and undergoes considerable modification from moment to moment. New elements enter the cluster and replace or are added to those which previously took part in the composition. An analogy might be made with a large cluster of electric lights arranged about a central predominant light, but so arranged that individual lights could be switched in and cut out of the cluster at any moment and different colored lights substituted. The composition and structure of the cluster, and the intensity and color of the light, could be varied from moment to moment, yet the cluster as a cluster maintained. We might carry the analogy farther and imagine the cluster to be an advertising sign which had a meaning—the advertisement. This meaning might or might not be altered by the changes in the individual lamps. The same indefiniteness pertains to the demarcation between the conscious and the subconscious. What was conscious at one moment may be subconscious the next and _vice versa_. Under _normal_ conditions there is a continual shifting between the conscious and subconscious. I have made numerous investigations to determine this point, and the evidence is fairly precise, and to me convincing, that this shifting continually occurs,[195] as might well be inferred on theoretical grounds. Nor, excepting in special pathological and artificial dissociated conditions, is the distinction between the conscious and subconscious at any moment always sharp and precise; it is often rather a matter of vividness and shading, and whether a conscious state is in the focus of attention or in the fringe. Experimental observation confirms introspection in this respect.