In considering the relation between psychology and the comprehensive science of sociology of which the study of politics forms part, this chapter presents an example of the relation between the social institution of warfare and the emotion of revenge. It proposes some examples of the same kind of principle which come more definitely into the realm of political science. Committees are of many kinds and work with very different degrees of success. One important distinction which could be made is according to the nature of their functions, and especially whether they are advisory or have executive functions. Modern psychology is largely concerned with the mechanisms by which certain mental products, and especially those products that are regarded as morbid, come into being. Among the many processes or mechanisms it has distinguished is one which is called the defence-mechanism.