Although means for measuring mental ability date as far back as 2000 b.c.e., when the ancient Chinese administered oral tests to determine a candidate's fitness for carrying out the tasks of civil administration, the modern intelligence test has its origins in the nineteenth century, when Jean-Étienne-Dominique Esquirol drew a clear distinction between mentally deranged people ("lunatics") and mentally retarded people ("idiots"). Esquirol believed that it was necessary to devise a means of gauging "normal" intelligence so that deviations from an agreed-upon norm could be ascertained, and he pointed out that intellectual ability exists on a continuum extending from idiocy to genius. His work coincided with studies in Europe and the United States that were designed to develop a concept of "intelligence" and to fashion a means of testing this capacity. Work done by Sir Francis Galton in the United Kingdom on hereditary genius, by James McKeen Cattell in the United States on individual differences in behavior, and by Hermann Ebbinghaus in Germany on tests of memory, computation, and sentence completion culminated in the 1905 Binet-Simon scale, created by Alfred Binet and Théodore Simon. It was the first practical index of intelligence measurement as a function of individual differences. This test was based on the idea that simple sensory functions, which had formed the core of earlier tests, are not true indicators of intelligence and that higher mental processes had to be included.
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