Motivation of Behaviour

aspects ... to explain how it is caused and how it is regulated." Professor Young has set himself a tremendous task. In order to accomplish it, he has, apart from breaking new ground, covered a very wide range both in theoretical and experimental psychology, particularly of the past ten yearsHe has endeavoured with no little skill to justify his thesis that in order scientifically to answer the question, " Why? " it is necessary not merely to give a description and attempt an explanation of purposive behaviour, but also to employ some method whereby it may he measured, and further to supplement both aspects by a genetic account of the development of motives. In his discussion of this branch, which he terms Energetics of Activity, or Biomechanics' Professor Young has amply illustrated his theories by reference to numerous experiments* both his own and those of others; and has concisely, but none the less critically, estimated the importance of their results as bearing upon 0lS problem. ,