Fluid intelligence, as defined by Cattell, is general to many fields and is used in tasks requiring adaptation to a new situation. Heredity is an important factor. The Culture Fair Intelligence Test is designed to measure fluid intelligence.

Crystallized intelligence, as defined by Cattell, is more specific to a given field such as education. This type of ability depends more on one's environment.

Intelligence tests are used to provide frame of reference for looking at cognitive abilities and making placement decisions on the basis of scores as well as for descriptive and predictive purposes.