The second influence in psychology tending to emphasize average tested ability is the establishment of the biological conception of the mind which recognizes the mutual interdependence of the mental processes, organically united through the activity of the brain. So long as intellectual, emotional and volitional processes are all mutually dependent, a disturbance of one aspect of mental life is bound to affect the others. In considering the mutual dependence of the mental processes, it is important to weigh carefully the striking examples which Bronner[4] has brought together, illustrating special abilities and disabilities. She has made an admirable start toward a differential diagnosis of special defects in number work, language ability and other mental activities. The degree of special deficiency which results in social failure could be placed upon an objective basis, but the rarity of special deficiencies as compared with general deficiency will make this a slow task. In the meantime we may rely upon the mutual dependence of the organic processes as a point of view which emphasizes the common spread of deficiency to many activities. Knowledge of a single case of specific disability is sufficient to make us recognize that such cases do occur. On account of the rarity of those cases and the absence of objective criteria, it seems necessary to leave the further differentiation to the future, considering here only those cases which may be grouped together as conative, as contrasted with those detected by our general intellectual tests. Whether the group of primarily conative cases is of any considerable size can be only very roughly estimated at present, since the diagnosis of such cases of feeble-mindedness rests at present almost exclusively on the subjective opinion of the examiner. Before their diagnosis is put upon an objective basis we must have a different form of test directed at such traits of will as initiative, perseverance, stability and self-control. These probably center on the mental side around the instinctive emotional background of interest and the passions, while, on the physical side, they raise the question whether the subject's energy is adequate to endure the strain of competition or whether it shows itself only in sudden bursts.