The Methods of Differential Psychology

The problems of differential psychology are numerous and difficult. Which paths must we take in order to master them? We shall see that all the methods that have been developed in general psychology can also be pressed into service for our purposes. They will simply be organized differently. We shall subdivide these methods into six categories which, admittedly, owe their origins less to logical than to opportunistic reasons: self-observation, observation of others, consideration of history and poetry, cultural studies, mass investigations (surveys), and experiment. Of these, the first five will concern us only briefly; the last of them, however, we shall consider more extensively.