Louis L. Thurstone (1887–1955), a pioneer in psychometrics and psychophysics, rejected Charles Spearman’s concept of a single, overarching General Intelligence factor (g). Instead, Thurstone utilized multiple-factor analysis, specifically developing centroid factor analysis, to demonstrate that intelligence consists of a constellation of relatively independent group factors.
- Primary Mental Abilities (PMA): Thurstone originally isolated over 50 cognitive abilities, which he later reduced to 7 core independent factors in his seminal 1938 work, Primary Mental Abilities.
- Independence of Factors: Unlike Spearman's hierarchical model where 'g' dominates, Thurstone posited that these primary abilities operate independently during complex problem-solving, though a weak positive intercorrelation (second-order 'g') is often observed.
- Historical Significance: This model paved the way for modern multi-faceted intelligence frameworks, most notably J.P. Guilford's Structure of Intellect (SI) model and Howard Gardner's Theory of Multiple Intelligences.