In short: fluid intelligence is the ability to reason and solve problems you have never met before, such as working out the rule in an unfamiliar puzzle. Crystallized intelligence is the knowledge and skills you have built up through learning and experience, such as vocabulary and general knowledge. Fluid ability peaks in early adulthood and then slowly declines, while crystallized ability keeps growing well into later life. The psychologist Raymond Cattell first described the two in 1943.
What is fluid intelligence?
Fluid intelligence, often written Gf, is the ability to think logically and solve new problems, independently of what you have learned. It is what you use when there is no rule to remember and no answer to look up: you have to spot the pattern, try an idea and adjust. Raymond Cattell, who named it, described it in 1943 as "a purely general ability to discriminate and perceive relations" (quoted in Brown, 2016).
In psychology, a simple definition is that fluid intelligence is the ability to reason, see relationships and solve unfamiliar problems on the spot. It works closely with working memory, holding information in mind while you use it, and it is measured with tasks that are deliberately new to everyone, such as abstract pattern puzzles.
Examples of fluid intelligence
- Working out the rule in a number series or a grid of shapes you have never seen.
- Finding your way around a city you are visiting for the first time, using only a map.
- Figuring out a new board game, app or gadget without reading the instructions.
- Solving a logic puzzle, such as a seating plan, from a set of clues.
- Seeing what has gone wrong in an unfamiliar situation and improvising a fix.
What does high fluid intelligence mean?
Someone with high fluid intelligence picks up new rules quickly, copes well with complex or unfamiliar problems and needs fewer examples before a pattern clicks. Fluid ability is very closely tied to general intelligence, the g factor behind all IQ tests. A 2008 Swedish study of more than 3,500 people put the link between fluid intelligence and g at 0.83 across the whole sample, and close to 1 within groups who had similar chances to learn (Kvist and Gustafsson, 2008). That is why fluid reasoning puzzles sit at the heart of most IQ tests.
What is crystallized intelligence?
Crystallized intelligence, or Gc, is the store of knowledge and skills you have built up through education, reading and experience, together with your ability to use it. Vocabulary, facts, the rules of grammar, arithmetic you know by heart and expertise in your job all count. Cattell described it as "discriminatory habits long established in a particular field". British texts often spell it crystallised; the theory itself uses Cattell's American spelling.
In psychology, a simple definition is that crystallized intelligence is the ability to use learned knowledge, skills and experience. Because it depends on what you have had the chance to learn, it is shaped far more by education, language and culture than fluid intelligence is.
Examples of crystallized intelligence
- Knowing what words such as "reluctant" or "ambiguous" mean.
- Remembering historical facts, capital cities or how your country is governed.
- Doing your times tables, or applying a formula you learned at school.
- Using grammar correctly and spotting the mistake in a badly written sentence.
- Drawing on expertise built up at work, such as a mechanic recognising an engine fault by its sound.
Fluid vs crystallized intelligence: the key differences
| Feature | Fluid intelligence (Gf) | Crystallized intelligence (Gc) |
|---|---|---|
| What it is | Reasoning with new information | Using knowledge you already have |
| The question it answers | "How do I solve this?" | "What do I know about this?" |
| Everyday examples | New puzzles, unfamiliar games, logic problems | Vocabulary, facts, times tables, job know-how |
| Typical test tasks | Matrix reasoning, figure weights, number series | Vocabulary, similarities, general knowledge |
| With age | Peaks in early adulthood, then slowly declines | Keeps rising until at least 60 |
| Shaped by schooling and culture | Less, by design of the tests | Strongly |
The two are not separate compartments. People who score well on one tend to score well on the other, and almost every real task uses both: you need crystallized knowledge of the words in a puzzle and fluid reasoning to solve it.
Fluid or crystallized? Sort the examples
Here are eight everyday tasks. Decide whether each one mainly calls on fluid or crystallized intelligence. Most real tasks use some of both, so go with the main one.
Fluid or crystallized?
0 of 8 answered
How fluid and crystallized intelligence change with age
The clearest difference between the two shows up across a lifetime. Fluid-type abilities rise quickly through childhood, peak in early adulthood and then slowly decline. Crystallized abilities keep growing for decades, because you never stop adding to what you know. John Horn and Raymond Cattell set out this pattern in a classic 1967 study of age differences, and large modern studies have confirmed it.
When different abilities peak
Age at which performance was highest, by ability
- Processing speeddigit-symbol coding
- late teens
- Short-term memory for names
- about 22
- Digit spanrepeating numbers
- early 20s
- Working memoryvisual and verbal
- about 30
- Memory for faces
- about 30
- Reading emotions in facesbroad peak
- 40s to about 60
- Vocabularytest norms and online data
- about 50 to 65
Processing speed peaked first, in the late teens. Short-term memory for names and digit span peaked in the early 20s, and working memory around 30. Reading emotions in faces stayed near its best from the 40s to about 60, and vocabulary peaked latest of all: around 50 in the test norms and about 65 in the online data. Knowledge subtests such as general information and comprehension also peaked later than almost every other task. You can check your own memory with our free photographic memory test.
Decline starts earlier than many people expect. Timothy Salthouse concluded that "some aspects of age-related cognitive decline begin in healthy educated adults when they are in their 20s and 30s", while vocabulary and general knowledge kept increasing until at least 60 (Salthouse, 2009).
None of this means your IQ score falls as you get older. An IQ score compares you with people of your own age, so the average stays at 100 at every age. Our guide to average IQ by age explains how that works.
How the two work together: Cattell's investment theory
Cattell argued that crystallized intelligence grows out of fluid intelligence. Through childhood and beyond, you invest your fluid ability in learning, reasoning your way through new words, ideas and skills, and what you learn settles into lasting knowledge. The names capture the idea: fluid ability can take the shape of any problem, while crystallized knowledge has set into a fixed form.
The theory makes a testable prediction. If fluid ability feeds learning in every area, it should be almost the same thing as general intelligence. That is what Kvist and Gustafsson found in their 2008 study of Swedish-born and immigrant participants: the link between fluid intelligence and g was close to perfect within groups who had similar opportunities to learn, and they read this as support for the investment theory. It also explains why crystallized intelligence depends on opportunity. Two people with the same fluid ability can end up with very different knowledge if one had far more schooling.
Where the theory came from
- 1938John C. Raven publishes the Progressive Matrices, a non-verbal pattern test later used as a measure of fluid reasoning.
- 1941–1942Donald Hebb describes "intelligence A", direct intellectual power, and "intelligence B", established ways of responding, an idea Cattell builds on.
- 1943Raymond Cattell first uses the terms fluid and crystallized intelligence in "The measurement of adult intelligence".
- 1963Cattell publishes "Theory of fluid and crystallized intelligence: a critical experiment", his first full test of the idea.
- 1966–1967Cattell and John Horn refine the theory and map how the two abilities differ across age groups.
- 1990s–2000sGf and Gc become broad abilities in the Cattell-Horn-Carroll (CHC) model, a framework now used to design and interpret many IQ tests.
Sources: Brown (2016) on Hebb and the origin of the terms; Cattell (1943, 1963); Horn and Cattell (1966, 1967); McGrew (2009) on CHC theory; Lancaster University's psychology glossary on Raven's Progressive Matrices.
How fluid and crystallized intelligence are tested
Fluid reasoning tests
Fluid tests use material that is new to everyone, so prior knowledge helps as little as possible. The classic example is Raven's Progressive Matrices: each item is a pattern with a piece missing, and you choose the piece that completes it. In the adult Wechsler IQ test (WAIS-5), the Fluid Reasoning index uses Matrix Reasoning, completing a grid of patterns, and Figure Weights, working out which shapes keep a set of scales balanced.
Crystallized intelligence tests
Crystallized tests ask what you know. The WAIS-5 Verbal Comprehension index uses Vocabulary, explaining what words mean, and Similarities, saying how two words or ideas are alike. General-knowledge questions are another common format. Because the answers depend on language and schooling, a crystallized intelligence test only makes sense for people who share the language and broad education it was built for.
Which does an online IQ test measure?
Most online IQ tests, including ours, lean towards fluid reasoning. The Assessivo IQ test is built mostly from new patterns, logic puzzles, shapes and number rules. A few logic questions use simple word analogies, but there is no vocabulary or general-knowledge section, so it tells you much more about your fluid than your crystallized intelligence. Our sample IQ test questions show each type, and our guides to abstract reasoning and verbal reasoning go deeper into the fluid and crystallized sides.
Can you improve fluid or crystallized intelligence?
Crystallized intelligence is the easy one: it grows whenever you learn. Reading widely, studying, picking up a skill or a language and taking on new kinds of work all add to it, at any age.
Fluid intelligence is much harder to move. In 2008, a widely reported study found that training on a demanding memory game, the dual n-back, improved scores on a fluid reasoning test (Jaeggi and others, 2008). The broad claim did not hold up. A 2016 meta-analysis of 87 publications found that working memory training improved the skills people practised, but gave no convincing gains in intelligence or other "far transfer" measures (Melby-Lervåg and others, 2016). A major review of brain-training programmes the same year reached a similar conclusion: people get better at the games they play, with little evidence that the gains spread to everyday thinking (Simons and others, 2016).
Education is the clearest exception. A 2018 meta-analysis covering more than 600,000 people found that each extra year of education raised IQ by roughly 1 to 5 points, and the effect showed up on every broad type of cognitive ability the researchers looked at (Ritchie and Tucker-Drob, 2018). Our guide to whether you can increase your IQ weighs this against adoption studies, preschool programmes and popular shortcuts.
Fluid and crystallized intelligence: quick definitions
If you are revising for a psychology exam, such as AP Psychology or A-level Psychology, these are the short versions.
Memory aid: fluid flows into the shape of any new problem; crystallized has set into solid knowledge. Both terms come from Raymond Cattell (1943), who developed the theory with John Horn.
Frequently asked questions
What is the main difference between fluid and crystallized intelligence?
Fluid intelligence is the ability to reason and solve problems that are new to you, without relying on what you have learned. Crystallized intelligence is the knowledge and skills you have built up, such as vocabulary, facts and know-how. Put simply, fluid intelligence is how you think on the spot, and crystallized intelligence is what you know.
Is IQ fluid or crystallized intelligence?
Both. A full professional IQ test such as the WAIS-5 includes fluid reasoning tasks, such as matrix puzzles, and crystallized tasks, such as vocabulary, and combines them into one full scale IQ. Some tests, such as Raven's Progressive Matrices, focus mainly on fluid reasoning.
At what age does fluid intelligence peak?
In early adulthood for most fluid-type skills. In a 2015 study of tens of thousands of people, processing speed peaked in the late teens and working memory around 30, while vocabulary did not peak until about 50 to 65. Timothy Salthouse found that some decline in reasoning and speed begins in healthy adults in their 20s and 30s.
Does crystallized intelligence decline with age?
Much later than fluid intelligence, if at all for many people. Studies usually find vocabulary and general knowledge rising until at least 60, and in one large online study vocabulary peaked at about 65.
Which is more important, fluid or crystallized intelligence?
Neither on its own. Fluid intelligence matters most for unfamiliar problems and for learning new things quickly. Crystallized intelligence lets you use what you already know, which most everyday work relies on. In Cattell's investment theory the two feed each other: fluid ability is invested in learning and becomes crystallized knowledge.
Can you increase fluid intelligence?
There is little good evidence that brain-training games do it. A 2016 analysis of 87 publications found that working memory training improved the trained skills but produced no convincing gains on measures of intelligence. Education does help: each extra year of schooling is linked to a gain of roughly 1 to 5 IQ points.
Is memory fluid or crystallized intelligence?
It depends on the kind of memory. Working memory, holding information in mind and using it for a few seconds, follows the fluid pattern and peaks around 30. Long-term knowledge you can recall, such as facts and the meanings of words, is crystallized intelligence.
Who came up with fluid and crystallized intelligence?
The psychologist Raymond Cattell, who first used the terms in a 1943 paper. He drew on Donald Hebb's similar idea of "intelligence A" and "intelligence B", and later developed the theory with the psychologist John Horn. Today both are broad abilities in the Cattell-Horn-Carroll (CHC) model, which underpins many modern IQ tests.
What do Gf and Gc stand for?
Gf is the usual shorthand for general fluid intelligence and Gc for general crystallized intelligence. The G reflects the fact that each is a broad, general ability that shows up across many different tasks.
Sources
- Cattell, R. B. (1943). The measurement of adult intelligence. Psychological Bulletin, 40(3), 153–193.
- Cattell, R. B. (1963). Theory of fluid and crystallized intelligence: a critical experiment. Journal of Educational Psychology, 54(1), 1–22.
- Horn, J. L. and Cattell, R. B. (1966). Refinement and test of the theory of fluid and crystallized general intelligences. Journal of Educational Psychology, 57(5), 253–270.
- Horn, J. L. and Cattell, R. B. (1967). Age differences in fluid and crystallized intelligence. Acta Psychologica, 26, 107–129.
- Brown, R. E. (2016). Hebb and Cattell: the genesis of the theory of fluid and crystallized intelligence. Frontiers in Human Neuroscience, 10, 606.
- Hartshorne, J. K. and Germine, L. T. (2015). When does cognitive functioning peak? The asynchronous rise and fall of different cognitive abilities across the life span. Psychological Science, 26(4), 433–443.
- Salthouse, T. A. (2009). When does age-related cognitive decline begin? Neurobiology of Aging, 30(4), 507–514.
- Valentin Kvist, A. and Gustafsson, J.-E. (2008). The relation between fluid intelligence and the general factor as a function of cultural background: a test of Cattell's investment theory. Intelligence, 36(5), 422–436.
- McGrew, K. S. (2009). CHC theory and the human cognitive abilities project. Intelligence, 37(1), 1–10.
- Jaeggi, S. M., Buschkuehl, M., Jonides, J. and Perrig, W. J. (2008). Improving fluid intelligence with training on working memory. Proceedings of the National Academy of Sciences, 105(19), 6829–6833.
- Melby-Lervåg, M., Redick, T. S. and Hulme, C. (2016). Working memory training does not improve performance on measures of intelligence or other measures of "far transfer". Perspectives on Psychological Science, 11(4), 512–534.
- Simons, D. J. and others (2016). Do "brain-training" programs work? Psychological Science in the Public Interest, 17(3), 103–186.
- Ritchie, S. J. and Tucker-Drob, E. M. (2018). How much does education improve intelligence? A meta-analysis. Psychological Science, 29(8), 1358–1369.
- Raven's Progressive Matrices (RPM), Lancaster University psychology glossary: the 1938 test and its use as a fluid measure.
- Wechsler Adult Intelligence Scale, Fifth Edition, Pearson: the WAIS-5 and its index scores.
Put your fluid reasoning to the test
Take the free Assessivo IQ test: 36 questions on fluid, logical, spatial and numerical reasoning, with your estimated IQ score and percentile as soon as you finish.
Take the free IQ test
