A fundamental factor (2) of human intelligence, derived from factor analysis, corresponding roughly to non-verbal reasoning, requiring rapid understanding of novel relationships, measured by tests such as Raven's Progressive Matrices. The concept was introduced in an article by the English-born US psychologist Raymond B(ernard) Cattell (1905–98) in the journal Psychological Bulletin in 1941 and became widely known after the publication of his book Abilities: Their Structure, Growth and Action (1971). Also called fluid ability. Compare crystallized intelligence. Gf abbrev.