In the 1940’s, psychologist Raymond B. Cattell attempted to create “culture-free” tests of intelligence. Believing that IQ tests contain implicit biases in favor of particular cultures, he sought to apply factor analysis to partition the g factor of intelligence (as measured by IQ) into two components–fluid and crystallized. He described fluid intelligence, as “a capacity to perceive relations and educe correlates.” In essence, this is the capacity for new conceptual learning, abstraction, and problem solving and is measured by relatively culture-free tests such as Raven’s Progressive Matrices. (See: What are the best tests for measuring your IQ? – Intelligence and IQ) In contrast, crystallized intelligence, is that part of intelligence that has grown out of acquired intellectual skills and distilled from learning experiences. Cattell defined it as “cognitive performance in which skilled judgment habits have become crystallized as the result of earlier learning application of some prior, more fundamental general ability to these fields.”
For example, a child’s proficiency at the game of tic-tac-toe would be mainly a measure of her fluid intelligence, if she had just learned the game; however, if she had played enough to learn the importance of occupying the center and corner squares, her proficiency could derive from this acquired (crystallized) knowledge.
Some researchers believe that fluid intelligence grows quickly after birth reaching its maximum power in the late teens or early 20’s and then declining gradually toward dotage. (See figure above). This might explain why so many mathematicians and physicists have reached the pinnacle of their creativity before age 30. (For example, Einstein’s annus mirabilis was 1905, the year he turned 26.) Crystallized intelligence, on the other hand, increases over time as learning experiences accumulate. The graph of crystallized cognitive ability in the above figure reveals that this component of intelligence can continue to increase into old age, although it varies significantly across individuals depending upon the intellectual richness of their environment in the years following their formal education.
When the contributions to g from fluid and crystallized intelligence are added, we obtain the combined cognitive ability g shown in the top graph of the same figure. It displays a maximum ability when a person reaches their early 50’s, because the added experience yields an increase in crystallized intelligence that more than compensates for the decrease in fluid intelligence. This may explain the difference between fluid intelligence and wisdom. In youth, our fluid intelligence is highest. We are at the peak of our abilities in problem solving and abstract thinking, where substantial accumulated experience is less important. However, we are unsuited to serve, for example, on the Supreme Court where precedent and prior knowledge are vital to the insightful judgement that we call “wisdom.”
While crystallized intelligence is significantly affected by the learning environments of our youth, fluid intelligence is an innate part of general intelligence, and directly related to our brain physiology. Hence it is mainly genetic and mostly inherited. Though the graphs in the top figure suggest that the fluid and crystallized factors make approximately equal contributions to general cognitive ability, the relative importance of these two factors will vary significantly depending on the individual and on the environmental circumstances. Poor learning environments will suppress the crystallized cognitive ability, while rich learning environments will enhance it. As more research is undertaken, we will be able to assess the relative importance of different learning environments, and hence the power of family and school to enhance g. Such research will also shed light on the extent to which intelligence is inherited and the role played by epigenetic factors.
