To illustrate concretely: in an office employing twenty stenographers on correspondence, it is not only necessary for the employer to know which of these stenographers is the most competent and which the least and whether the less competent are incapable merely because they are beginners or because they lack the necessary mental capacity ever to become competent. He should also be able to measure the mental capacity of the entire group by some standard based upon the performance of thousands and tens of thousands of stenographers of known degrees of ability. He may discover that the most competent of his entire staff is only as capable as the average of good stenographers everywhere. Obviously, his business is handicapped by having a stenographic force which is inferior in capacity and, consequently, in accuracy, speed, and other essential requirements, to the average of stenographic office staffs in business generally. Once this has been determined, the intelligent employer will proceed to replace the stenographers who are incapable of improvement, as indicated by the tests applied, with stenographers who respond to the standard tests with a score well above the average. So, too, with the teacher. It is comparatively easy for the teacher to classify his or her pupils into bright, stupid, and mediocre, through observation alone. What is more important, however, is to determine several things about each pupil which observation alone does not tell. Are the stupid ones really stupid or merely inattentive? Have they the necessary mental capacity to perform the assigned work of the class or are they simply lazy? Few teachers can answer this question; none with any degree of accuracy without the application of scientific tests of mental capacity. Are the bright children really bright by comparison with other children of the same age and school grade or do they merely shine by contrast with the dull members of the class? This question can by no means be answered accurately except by the application of mental capacity tests. In another chapter some of the concrete applications of mental tests in education are described at length. The point to be emphasized here is that the measurement of the mental capacities of any group should be based upon standards that will not only determine the relative capacities of the members of the group but will, at the same time, compare them all with standards that reflect the known average and maximum capacities of all others of similar age and environment. The purpose of these tests might be summed up somewhat as follows: _To measure, by comparison with the group average or with very carefully determined standards, some of the infinite number of qualities and abilities, the possession of which by the individual renders him more or less susceptible to education and training or more or less capable of successfully performing certain actions requiring conscious direction from the mind._