In these occupations the degree of intelligence is by no means the sole determinant of either successful or satisfactory performance. Temperamental characteristics, such as those enumerated by Schneider and by Thorndike, the local and wandering inclinations, active and sedentary dispositions, tendencies to competitiveness, imitation, suggestibility, sympathy, curiosity, and the entire series of instinctive propensities, dominant original or acquired types of satisfaction and annoyance, attitudinal, volitional and emotional differences, and the moral and social traits, such as persistence, frankness, piety, loyalty, zeal, all these may be expected to combine in varying relations of compensation and reenforcement, substitution and facilitation. What one lacks in quickness it is often possible to make up in persistence; what another lacks in ambition and competitiveness he may supply in the form of loyalty and zeal; relative intellectual inferiority is often and easily balanced by the display of social charm; persistent, well-directed and enthusiastic effort or even a good vocabulary may enable one to compete successfully with the exceptional genius who does not display these incentives or advantages. In the proposals to direct individuals into their proper life careers, the advocates have quite commonly failed to make sufficient allowance for the overwhelming importance of incentive, motive, attitude and purpose, and the large role they play in determining the possible achievements of a nervous system. It is well enough to test the memory span, attention type, and reaction time of an applicant for a job as motorman on a street car. It is still more important to learn the strength of his instinctive competitive reactions, to measure the degree of his belief in hell or in socialism, or the firmness of his intention to effect the higher education of his children. By "more important" I mean better calculated to reveal his fitness for the work. I would rather trust my life and limb to a motorman whose feeble memory span is reenforced by a loyal devotion to the comfort of his grandmother than to a mnemonic prodigy whose chief actuating motive in life is to be a "good fellow." These comments should not be construed as an underestimation of the usefulness of the simple intellectual test as a preliminary precaution in engaging employees or in detecting extreme departures from the mode or average. The use of such tests in discovering such departures and variants as idiocy, imbecility and general stupidity has been amply justified by experience with them. But we are primarily concerned here with the determination of individual differences and qualifications within the large middle range of the curve of distribution. My conviction is that, in the case of the average individual, we must either: