Fluid intelligence (Gf) is the ability to reason and solve new, unfamiliar problems while relying almost not at all on accumulated knowledge. It is contrasted with crystallized intelligence (Gc) — the store of knowledge and skills built up over a lifetime.
Fluid versus crystallized
In Cattell–Horn theory, fluid intelligence is "pure" reasoning: recognizing a pattern, solving a logical puzzle, finding a rule. It is measured, for example, by Raven's Progressive Matrices. Crystallized intelligence is vocabulary, general knowledge and mastered techniques; it is tested with vocabulary and general-knowledge tests.
Different aging trajectories
The key difference is in how they change with age. Fluid intelligence peaks in young adulthood (around 20–30 years) and then gradually declines. Crystallized intelligence, on the contrary, grows and holds up for decades, beginning to fall noticeably only after 65. So an older person may lag in the speed of solving new problems but surpass others in experience and vocabulary.
What affects it
Fluid intelligence relies on the prefrontal cortex, processing speed and working memory: their age-related decline is what drags Gf down. It was precisely a rise in Gf that "brain trainers" like dual n-back promised, but there is no convincing evidence of such transfer.
Calculate using this marker
Calculators where Fluid intelligence is used directly:
Frequently asked questions
How does fluid intelligence differ from crystallized?
Fluid is solving new problems “from scratch”, without relying on knowledge; it peaks early and declines with age. Crystallized is accumulated knowledge and vocabulary; it is stable and can grow into old age.
Can fluid intelligence be raised by training?
There is no reliable evidence of this. “Brain trainers” improve the exercises themselves, but transfer to fluid intelligence is not confirmed. Overall brain health is supported by sleep, exercise and learning.