department of research; the psychologist seeks knowledge and must employ all possible methods of knowledge in order to realize his purpose. Of course it is logically possible to make the empirical method the principle of union and to subsume all sciences employing it under one head. But that would be a superficial arrangement, neglecting, as it does, very important differences. There is a specific difference between the method of psychology and that of natural science. The method of psychology is primarily subjective or introspective, the method of science is objective. The psychologist studies the facts of the inner world, the physicist and physiologist those of the outer. The fields of study are different and the ways of handling them different in this specific sense. It is true the psychologist also uses the objective method, he pays attention to physical antecedents and accompaniments of mind, but his chief interest lies in consciousness; for the sake of this he regards the physical world. Even when he is occupied with the child and animal mind, introspection forms his basis and his guide. Only in case introspection is ruled out as worthless will this view fail, but in that event there can be no science of psychology, at least not in the sense in which this term has been understood down to the present time.
The introduction of the experimental method into psychology does not change this relation. It does not aim to do away with introspection; its object is rather to facilitate introspection, to render it more exact, to correct it, to bring it under control, to verify it. And as for measurement in psychology, well, we do not really measure mental states, but their physical concomitants. Besides, the measurement of the physical counterparts forms but a small and unimportant part of the problem of psychology. More or less exact numerical determination of this kind is possible only on the borderline of physics and psychology; only physical stimuli can be quantitatively determined, and such quantitative determination does not throw much light on the real problems of psychology. It is due to the appreciation of this fact that the trend toward psychophysics which characterized the beginnings of experimental psychology has been
