If we compare this interpretation of focus and margin with that of traditional psychology, we find that the latter construes the relation of the present to the future experience wholly in static terms, the functional relation being left out of account. The later experience is read back into its predecessor in the form of dim or marginal images, which need but show themselves more completely to make the two identical. If these sensations were intended only as symbols of a functional relationship, it would perhaps be scarcely worth while to enter a protest against them. But when the functional relationship is quite overlooked, the explanation that is given becomes exceedingly dubious. The ticking of the clock, for example, that is present, though unnoticed, the overtones of the note that suffuse the whole without diverting attention to their individual qualities,--in what precise way are facts of this kind concerned in the description of the experience which they modify? A study of the clock or of the overtones can hardly pass as an analysis of consciousness; it is too obviously an affair of physics. Such a study becomes merely an excuse for repeating the analyses of physics and reading them off in terms of sensations and images. Moreover, the transfer of all this material to consciousness looks suspiciously like a transaction in mental chemistry. Where, then, is psychology to gain a foothold? What is the meaning of these uncanny sensations and images, which nobody experiences, unless it be their character as symbols of adjustment? They have no legitimate status, and psychology, by consequence, has no legitimate problem, except in so far as they represent those possible acts of adaptation which are the sole and proper concern of psychology.
It remains to point out briefly the bearing of these results on what is called "the method of introspection." We are sometimes assured that introspection has discarded the belief in a separate mental stuff or subject-matter, but there is ground for the suspicion that such protestations are made in the same spirit that we affirm our belief in the Ten Commandments or the Golden Rule, with no thought of being taken seriously. At all events, without a literal "looking within" it seems to become exceedingly difficult to differentiate introspection from ordinary observation as practised in the other sciences. The reason for this difficulty is that there is nothing left in introspection by which it can be differentiated. The term introspection properly designates, not a method but a problem; the problem, namely, of interpreting given facts with reference to their function in the control of behavior. If psychology is to justify its claim to the status of a science, it is in duty bound to secure for itself both an objective criterion for the adjudication of disputes which otherwise are of necessity interminable, and a subject-matter that is not simply a heritage of metaphysical prejudice, but a realm of fact that is attested by everyday observation and experience.