The theory of fluid and crystallized intelligence was developed by Cattell and Horn (R. B. Cattell, 1941, 1950; 1971; Horn, 1965; Horn & Cattell, 1966), who used factor analysis to show that primary mental abilities such as reasoning ability, word fluency, verbal comprehension, facility with numbers, spatial visualization, and processing speed, can be organised into two principle classes of ability: fluid intelligence and crystallized intelligence. This conceptualization has withstood the test of time, and is widely used in cognitive neuroscience today.
Fluid intelligence (Gf or gF!) broadly captures our general reasoning ability. To quote from Jonassen & Hopkins (1993): “Gf represents different forms of reasoning including abstracting, forming and using concepts (classification), perceiving and using relations, identifying correlates, maintaining awareness in reasoning, and abstracting ideas, especially from figural and nonverbal… content” (p. 53). It has been described as the source of intelligence that an individual uses when he or she doesn’t already know what to do.
Crystallized intelligence (Gc) describes abilities depending on specific, acquired knowledge or expertise – the result of learning and acculturation. It is measured in tests of expert knowledge, general information, use of language (vocabulary) and is reflected in a wide variety of acquired, specific skills (Horn & Cattell, 1967). Educational and cultural opportunities are central to its development. Working memory capacity is closely related to fluid intelligence, and there is strong evidence that training working memory can improve fluid intelligence (Jaeggi et al, 2008).
People with a high capacity of Gf tend to acquire more Gc knowledge and at faster rates, and this has been called Gf investment.
The constructs of fluid and crystallized intelligence originally identified by Raymond Cattell. Cattell calls these factors ‘powers’, and says:
…it is apparent that one of these powers… has the ‘fluid’ quality of being directable to almost any problem. By contrast, the other is invested in particular areas of crystallized skills which can be upset individually without affecting the others.