[Psychological measurement from Binet to Thurstone, (1900-1930)]

The French psychologist Alfred Binet is at the origin of the development of the mental test intended for diagnosing the intellectual level of children. Initially conceived as clinical tests their importation to the United States during the 1910's has considerably altered their use, significance and interpretation. Turned into political tools by eugenicists and hereditarists and used in large-scale selection operations, the tests have changed the psychologists' conception of intelligence: initially conceived as multifacted and qualitative, intelligence had become a single quantifiable entity. Within this context, the American psychologist Louis Leon Thurstone criticized the lack of exactness of the statistical tools used in the intelligence scale. Once objectivized, his method became a general law intended to account for all mental processes.