THE SHORT ANSWER
What's the difference?
Fluid intelligence is the ability to reason through new problems without relying on prior knowledge. Crystallized intelligence is the knowledge and skills you have accumulated, such as vocabulary and facts. Fluid ability tends to peak in early adulthood; crystallized ability keeps growing well into later life.
Fluid
vsReasoning and problem-solving with new information
Accumulated knowledge, vocabulary and skills
Working memory, attention, processing speed
Education, reading, culture and experience
Matrices, number series, block design, analogies with novel shapes
Vocabulary, general knowledge, comprehension, verbal analogies
Early adulthood, roughly 20–30
Late in life: vocabulary often peaks in the 60s or later
Declines gradually from the late 20s
Stays stable or grows well into old age
Figuring out a new app with no instructions
Explaining the rules of a sport you know well
ACROSS A LIFETIMEFluid reasoning is near its peak. Crystallized knowledge is still building and will keep growing for decades.
One peaks young, the other keeps climbing
Drag through the ages. The curves are stylised from large cross-sectional studies; individuals vary a lot.
95%fluid, % of peak
82%crystallized, % of peak
QUICK QUIZ · 8 TASKS
Fluid or crystallized? Sort eight tasks
INVESTMENT THEORY
Fluid ability is spent to buy crystallized knowledge
Cattell argued that people invest their fluid reasoning in learning. Over years, what they work out becomes what they know. That's why the two are correlated, but not the same.
WHERE THE IDEA CAME FROM
From one idea to the theory behind modern IQ tests
1943Cattell's proposalRaymond Cattell suggests that general intelligence is really two abilities: fluid and crystallized.
1966Horn and CattellJohn Horn and Cattell test the idea and show the two abilities follow different paths with age.
1993Carroll's three strataJohn Carroll's re-analysis of 460+ datasets places Gf and Gc among broad abilities beneath a general factor.
2000sCHC theoryThe combined Cattell–Horn–Carroll model shapes modern tests such as the Woodcock–Johnson and Wechsler revisions.
MEASURE AND TRAIN BOTH