Cattell–Horn theory of intelligence
a theory proposing that there are two main kinds of intellectual abilities nested under general intelligence: g-c, or crystallized intelligence (or ability), which is the sum of one’s knowledge and is measured by tests of vocabulary, general information, and so forth; and g-f, or fluid intelligence (or ability), which is the set of mental processes that is used in dealing with relatively novel tasks and is used in the acquisition of g-c. In later versions of the theory, other abilities were added, such as g-v, or visual intelligence (or ability), which is the set of mental processes used in handling visual-spatial tasks (e.g., mentally rotating a geometric figure or visualizing what pieces of paper would look like if folded). [originated by Raymond B. Cattell in the 1940s; subsequently developed by U.S. psychologist John L. Horn (1928–2006) beginning in the
1960s]