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. III Within recent years the doctrine that psychology is a science of behavior has acquired a certain prominence. It is presupposed, of course, that the behavior with which psychology is concerned is of a distinctive sort; but the differentia is unfortunately the very thing that the "behaviorist" has hitherto left out of account. In his revolt against introspectionism, which has been accustomed to give to its subject-matter a subjectivistic and "psychic" interpretation, he goes to the other extreme and relies on behavior pure and simple. Being without a serviceable differentia, he is unable to mark off the field of psychology from contiguous territory. The selection of certain problems within the general range of behavior, with no recognition of any distinctive trait to guide and justify the selection, is hardly enough to warrant a new science. Even an arbitrary principle of selection is better than none, and it would, therefore, be quite as reasonable to subdivide the field of botany in the interests of a new science, and group together for separate botanical study those flowers which have enabled poets to give symbolic expression to the beauty of women.