The first is fluid intelligence, which Cattell defined as the ability to reason, think flexibly, and solve novel problems. It is what we commonly think of as raw smarts, and researchers find that it is associated with both reading and mathematical ability.[4] Innovators typically have an abundance of fluid intelligence. Cattell, who specialized in intelligence testing, observed that it was highest relatively early in adulthood and diminished rapidly starting in one’s thirties and forties.[5]
