In comparison with such sciences as Chemistry, Physics or Physiology, which have acquired a certain stability of doctrine and method, Psychology at the present day appears to have little of either of these characters; an excuse is often made to the effect that psychology is still one of the younger sciences, and has not as yet quite found a firm footing. The truth is that there are no clear-cut generally-accepted principles governing either the subject matter or methods of this science, as may be seen by consulting various text-books or that interesting volume of essays, Psychologies of 1930. Psychology may perhaps be considered young as an experimental science, but in regard to a part at least of its subject, it is about as old as any enquiry one can think of, for man has always been interested in man. Speculation on the existence and nature of ‘Soul,’ of mind, of thinking, of appetition, of character and conduct, reaches back to the centuries B.c., when Greek Philosophy was at its highest and best in the writings of Plato and Aristotle. These are subjects with which psychology to-day is still concerned, but having lost contact with the ancient philosohpy it has also lost a great deal of coherence.

It is this perhaps that accounts for the vagueness in the usage of the word ‘psychology’ to-day. But this very vagueness has certain advantages which must not be under-estimated, since it provides an incentive to research, and to scientific, that is to say methodical, investigation of the problems presented by human nature.