Crystallized and Fluid Intelligence

Abstract

The Gf-Gc theory of cognitive abilities is a psychometric theory of intelligence based on intelligence and ability tests. Evidence in favor of the theory has largely been gathered via factor analytic and developmental studies of intelligence, but also with respect to school/education achievement and biological/genetic evidence. The theory was first formulated in terms of fluid and crystallized cognitive abilities by Raymond Cattell in 1943. The theory posits its fundamental assumption, that intelligence (or rather, human cognitive abilities) is not a unitary construct but entails the lifelong coordination of at least two classes of abilities: fluid (Gf), which refers to the ability of understanding relationships among the components of an abstract problem and using such relationships to solve the problem, and crystallized (Gc), which refers to the knowledge accumulated through experiences. Fluid abilities are general in nature, in that they can be applied to any novel abstract situation that requires solving a novel problem, while crystallized abilities are specific, in that they require specific knowledge (learned from one’s cultural milieu) to solve familiar problems (this distinction is similar to, and partially built upon, what Donald Hebb proposed in 1942 in terms of Intelligence A and Intelligence B). Two particular aspects of this hypothesis, which set it apart from previous ones, are its structural and its kinematic predictions. Structural evidence in favor of the Gf-Gc hypothesis comes from many studies showing that by relying on factor-analytic methods it is possible to demonstrate that a single factor of intelligence, called g, does not describe the relations among broad cognitive abilities, representing primary-level abilities, as well as models with multiple factors. Kinematic predictions come from studies that analyze age gradients or, more directly, age changes in cognitive performance. These studies conclude that while during childhood both classes of abilities increase, starting in young adulthood fluid abilities decrease, while crystallized abilities remain constant (or may even increase). A third set of predictions is dynamic in nature, and it is captured especially by the investment theory, which postulates that during childhood fluid abilities are necessary to accumulate crystallized ones. In practice, it is certainly not simple to measure the two broadest abilities in adults; with respect to Gc abilities, because of the influence of experience, interest, motivation, professional skills, and years since schooling (on which most general Gc tests are based, like vocabulary); and as for Gf abilities, especially in older adults, processing speed generally decreases during adulthood, and most Gf tasks are timed, which leads to confounds between the two classes of cognitive tasks. Opponents of the theory have pointed out that, in practice, Gf is highly collinear with a general factor of intelligence (g), while Gc abilities further contribute little in terms of individual differences in cognitive performance.