Pre-Modern Ideas of Intelligence
Long before IQ tests, Plato and Aristotle theorized about reason, the soul, and wisdom. Explore pre-modern ideas about what makes a mind intelligent.
Galton and the Troubling Birth of Testing
Francis Galton pioneered measuring human ability β and founded eugenics. A clear-eyed look at the troubling roots of intelligence testing.
Binet and the First Real Intelligence Test
Alfred Binet built the first practical intelligence test to help struggling schoolchildren β not to rank or label them. Discover the Binet-Simon scale.
Spearman and the General Factor g
In 1904, Charles Spearman noticed that mental abilities correlate β and proposed a single general factor, g. Learn how factor analysis began.
Wechsler and the Modern IQ Scale
David Wechsler replaced mental age with the deviation IQ and built the WAIS and WISC β the scales that define IQ testing today.
The Flynn Effect and Its Reversal
Throughout the 20th century, IQ scores rose about three points per decade. Learn what drove the Flynn effect β and why it may now be reversing.
Fluid and Crystallized Intelligence
Raymond Cattell and John Horn split intelligence into fluid reasoning (Gf) and crystallized knowledge (Gc). Discover the theory behind the divide.
π
Last updated: 2026-06-18 Β· β Reviewed by the All-Lifes editorial team Β· About Β· Methodology