From a strictly psychological standpoint, the ideas and the not-ideas contain thus nothing but sensations. Their grouping, their shading, their combination, their succession decide whether we have before us a perception or an imagination, a volition or an emotion. What are we ourselves then for the psychologist? Evidently we ourselves belong also to the inner experiences which we know; and psychology has succeeded in analyzing this idea of our own self just in the same way as it analyzes our idea of the moon. In this analysis, psychology finds its idea of the self as a content of consciousness crystallized about the sensations from the body. Every one of our bodily activities is represented in our consciousness by movement sensations, and these sensations form the core of the complex aggregate which develops into the idea of ourselves. Organic sensations from our inner organs, pain sensations and pleasure sensations fuse with the movement sensations, and the whole complex shapes itself slowly into the idea of the personality of the self in contrast to the idea of other personalities. We ourselves are for ourselves a complex combination of sensations; and yet all our feelings and emotions and volitions are only a part of it. Psychology thus necessarily considers those experiences of feeling and will and character simply as changes in the midst of that central experience of personality which is itself made up of bodily sensations. Each bit of will and emotion must be decomposed into its finest elements. There is no passing mood, and no floating half-thought in our mind, no dream and no intuition, no slightest change of attention, no instinct and desire which cannot be analyzed thus into its sensation elements or rather which must not be analyzed, if we are to describe it at all, and that means if we are to give a psychological account. Psychology is endlessly far from this ideal to-day. It has been claimed, not without justice, that psychology has reached to-day only the level which physics attained in the seventeenth century; but psychology must insist that its ideal lies in this direction. No one takes a real psychological view of the human mind who does not understand this endless complexity of the material, and who does not see that even the simplest mental state practically presents a most complex problem to scientific analysis. The physician who really aims towards scientifically exact influence on the human mind has reached the first step of his preparation as soon as he understands that the content of consciousness is composed of hundreds of thousands of elements. To treat the mind as if there were only a few large pieces, one thing called memory and one thing called will and one called emotion and so on, is as if a surgeon were to perform an operation, knowing that there are arms and legs, but not knowing the ramifications of the nerves and blood-vessels which his knife may injure.