It is important to consider how the suggestion of XII as the upper limit of feeble-mindedness for adults got into the early practise in this country as the lower borderline for the mature. It is the most serious error which has marred investigations in this field. It seems to have been a case of repeated misunderstanding on the part of examiners for which nobody in particular was to blame. So far as I can determine nobody stated directly in connection with any scale what should be regarded as the lower borderline for the mature. Numerous examiners, however, in reporting their results, concluded that if the feeble-minded tested as high as XII then adults who tested XII were feeble-minded. They were somewhat encouraged in this fallacy by the fact that the 1908 scales suggested three years of retardation as an indication of feeble-mindedness, and the highest age-group of tests was soon shifted to fifteen years. The trouble seems to have been that early workers failed to recognize that some of the feeble-minded in institutions, the purely conative cases, have passable capacity so far as the brief intellectual tests are concerned. To determine scientifically what is the borderline, we should study randomly selected groups from the general population and determine the positions on the scale below which practically all are socially unfit. Or, as Wallin has suggested, we should find out the degree of tested ability necessary for survival in simple occupations that are afforded by society (_216_, p. 224). These positions can only be checked by finding the conditions in institutions or special classes. They cannot be determined by tests of these abnormal groups alone. Besides the confusion arising from these feeble-minded who are primarily unstable or inert, but with passable intellects, reasoning from the statistics on abnormal groups merely repeats a common fallacy. The fact that some inmates of institutions test XII does not let us know how many outside the institutions who test XII actually survive in society. The randomly selected groups of children on which Binet tried out his tests were so ridiculously small that he continually cautioned against adopting his suggestions as to borderlines as anything but tentative. For judging the borderline for the mature there were no test results which had not been seriously affected by the methods of selecting the groups, so we collected the data on this random group of Minneapolis 15-year-olds. I trust that this will make any examiner more careful about assuming that adults testing XI are clearly unable to survive socially, unless he is ready to claim that 10% of the general population are unfit socially.