These categories of definitions are not and perhaps cannot be mutually exclusive. They intersect and overlap at many points. PE. Vernon (1927) Intelligence is what intelligence test measures GD. Stoddard (1943) Intelligence is the ability to undertake activities Boring (1948) Intelligence is what intelligence tests. D. W. Wechster (1950) Intelligence is the aggregate or the global capacity of the individual to act purposefully, to think rationally and to deal effectively with the environment Evaluating on the basis of the above definition, we can calla person intelligent in proportion to his being able to use his mental energy in handing his actual life problems and leading a happy and well contented life.