The economists are called upon to play two  distinct roles: (a) as educationists and (b) as professional economists. As teachers, they are concerned with explaining past economic experience and to instruct in the tools and techniques of economic analysis. The professional economists arc involved with discovery and prediction. They are interested in developing and applying techniques that will help them in predicting future economic events. The tools arc expository, analytical and illustrative devices. But they 00 not represent facts. TIhey can be used to illustrate a case, but they can seldom be used to demonstrate a case.