From the INTRODUCTION. The measurement of intelligence at the present time is a well recognized part of psychology. The growth of this work and the interest shown in it during the last three decades have been truly remarkable. We have witnessed the establishment of innumerable clinics and the appearance of the "mental tester." This growth has been characterized by the practical considerations of clinical examinations. The need for a psychological examination has been recognized and answers to practical situations have been (...) demanded before the psychologist has really had time to formulate his own conceptions of the whole problem. Theoretical considerations have lagged behind the practical application of mental tests. We have been measuring intelligence long before we have decided as to what intelligence really is. Far from being a drawback, as this at first sight would appear to be, it has in fact proved' to be of distinct advantage, since the measurement of this something, that we have been making, is leading us slowly but surely to a real knowledge of what can with profit be called "general intelligence." Only after considerable work with mental tests did psychologists arrive at the now generally accepted definition of intelligence, as enunciated by Stern, that "Intelligence is a general capacity of an individual consciously to adjust his thinking to new requirements: it is general mental adaptability to new problems and conditions of life." Although even this definition of intelligence may be modified in the future, it serves, at the present time, as a good working hypothesis for the selection of tests for mental measurement. Other conceptions of general intelligence are numerous and many are very similar. Binet, for example, says: "It seems to us that in intelligence there is a fundamental faculty, the alteration or the lack of which is of the utmost importance for practical life. This faculty is judgment, otherwise called good sense, initiative, the faculty of adapting one's self to circumstances. To judge well, to comprehend well, to reason well, these are the essential activities of intelligence." Meumann says general intelligence depends on two qualities, "(1) on the capacity for independent, productive thought (productive, synthetic thinking).... (2).the intensity of the whole mental life." Ebbinghaus makes intelligence include abstraction and the ability to compare and contrast. Burt says that the result of his work "strongly suggests that it is one feature or function of attentive consciousness which forms the basis of intelligence, namely, the power of readjustment to relatively novel situations by organizing new psycho-physical co-ordinations." And lastly Hart and Spearman look upon general intelligence as a "common factor" or "central tendency" not exactly definable, but entering into all sorts of mental activities to a greater or less degree. In addition to these hypotheses as to the nature of intelligence, theoretical considerations as to the growth of intelligence and the general distribution of the various grades of intelligence are arising as a direct result of the practical work being done. Questions as to the rate of increase in normal mentality are being raised, and the theoretical assumptions, upon which we base our classification of individuals into different groups, are being discussed. (shrink)