The types of intelligence that psychologists actually measure come from the Cattell–Horn–Carroll (CHC) model: a general ability, often called g, sitting above roughly a dozen broad abilities such as fluid reasoning, crystallized knowledge, working memory, visual-spatial processing and processing speed. The most famous distinction is between fluid intelligence, the ability to solve problems you haven't seen before, and crystallized intelligence, the knowledge and vocabulary you have built up.
These are not separate "intelligences" in the sense of independent talents. People who do well on one tend to do well on the others, which is why a single overall IQ score is meaningful. But the profile underneath that score can be uneven, and the differences matter in daily life.
Where the CHC model comes from
In the 1940s and 1960s Raymond Cattell, and later his student John Horn, argued that intelligence splits into at least two broad parts: fluid (Gf) and crystallized (Gc). Horn extended the list to several more broad abilities. In 1993, John Carroll published a reanalysis of more than 460 data sets from decades of ability testing and arrived at a three-level structure: many narrow skills at the bottom, a smaller set of broad abilities in the middle, and a general factor at the top.
Kevin McGrew and others combined these accounts into the CHC model in the late 1990s and 2000s (McGrew, 2009), and Schneider and McGrew (2018) gave the current detailed version. Most modern IQ batteries are built around or interpreted through this model: the Woodcock-Johnson is designed on it, and the Wechsler indexes map onto it even though their names differ. Our own test uses six CHC-based domains for the same reason; the methodology page lists them.
The main CHC broad abilities
| Code | Ability | Everyday example |
|---|---|---|
| Gf | Fluid reasoning | Figuring out an unfamiliar board game from the first few moves |
| Gc | Comprehension-knowledge (crystallized) | Understanding a dense news article; knowing what "fiduciary" means |
| Gq | Quantitative knowledge | Estimating a tip or checking whether a loan offer adds up |
| Grw | Reading and writing | Drafting a clear email; reading a contract accurately |
| Gwm | Working memory capacity | Holding a phone number in mind while you find a pen |
| Gl / Gr | Learning efficiency / retrieval fluency | Remembering new colleagues' names; quickly listing ideas in a brainstorm |
| Gv | Visual-spatial processing | Packing a car trunk; reading a map without turning it |
| Ga | Auditory processing | Following a conversation in a noisy restaurant; hearing a wrong note |
| Gs | Processing speed | Scanning a spreadsheet for errors quickly and steadily |
Schneider and McGrew list several more, including reaction time, psychomotor speed, domain-specific knowledge, and abilities tied to the other senses. They also treat the list as a working map that gets revised as evidence comes in, not a finished catalog. In the 2018 version, for example, the older "long-term storage and retrieval" ability (Glr) was split into learning efficiency (Gl) and retrieval fluency (Gr).
Fluid vs crystallized intelligence
Fluid intelligence (Gf) is reasoning with new information: spotting patterns, forming and testing rules, and solving problems where memorized knowledge doesn't help. Matrix puzzles, where you choose the piece that completes a grid of shapes, are the classic test.
Crystallized intelligence (Gc) is the depth and breadth of what you know and can put into words: vocabulary, general knowledge, and understanding of how things work in your culture. Vocabulary and general-information questions are the classic tests.
The two follow different paths across the lifespan. On average, fluid reasoning peaks in early adulthood and declines gradually afterward, faster in later life, while crystallized knowledge keeps growing or holds steady well into later adulthood. That is one reason a 60-year-old can be slower on a novel puzzle than a 25-year-old and still outperform them on a test of word meaning. (See how IQ changes with age for why age-normed scores hide these shifts.)
Cattell's "investment" idea links the two: you invest fluid ability, along with time, schooling and interest, into learning, and what you learn becomes crystallized knowledge. In practice the two correlate strongly, and both load heavily on the general factor. A person with high Gc and lower Gf usually learned well through reading and experience; the reverse profile is common in young people who reason quickly but haven't had time to accumulate knowledge.
Working memory, and why it shows up at work
Working memory is the mental workspace that holds a few pieces of information while you use them: keeping the first half of a sentence in mind while you read the second, or tracking three numbers while you add a fourth. Its capacity is small for everyone, and it fills quickly. On IQ tests it is measured with tasks like repeating digits backward or in sorted order.
At work, working memory limits show up as lost threads. You get interrupted mid-calculation and have to start over; you join a call and forget the point you were about to make. Some practical consequences follow directly:
- Externalize. Writing steps down, using checklists, and keeping a scratch file move information out of a small, fragile store and onto a page that does not forget.
- Protect hard thinking from interruption. Every interruption forces you to rebuild what was in working memory.
- Chunk. Experts appear to hold more in mind because familiar patterns compress into single units. A chess master sees a known opening, not twelve separate pieces.
Working memory training apps reliably improve performance on the trained tasks, but evidence that the gains spread to general reasoning is weak. Better systems tend to help more than trying to enlarge the workspace itself.
Cognitive load, multitasking and decision fatigue
Cognitive load is the demand a task places on working memory. When load exceeds capacity, errors rise and learning drops. That is uncontroversial, and it is why clear instructions, worked examples and reducing clutter help people learn complex material.
Multitasking, for tasks that need attention, mostly means switching rapidly between them. Laboratory research on task switching (reviewed by Monsell, 2003) shows a consistent cost: responses are slower and more error-prone immediately after a switch, even when people know a switch is coming. Doing two demanding things "at once" is usually slower in total than doing them one after the other.
Ego depletion and decision fatigue are on much weaker ground than their popularity suggests. Ego depletion is the idea that self-control draws on a limited resource that gets used up. It was supported by many small studies, but a large preregistered replication across 23 labs and more than 2,000 participants found an effect close to zero (Hagger et al., 2016). Researchers still debate whether a smaller or more specific version exists.
Decision fatigue became famous through a study of Israeli parole boards, which reported that favorable rulings fell sharply as judges worked through a session and recovered after food breaks (Danziger, Levav, & Avnaim-Pesso, 2011). Critics pointed out that case order was not random. For example, prisoners without lawyers tended to be heard later in a session, and that ordering could produce the same pattern without any fatigue. Tiredness from long, demanding work is real. A specific, depleting "decision budget" has not been well established.
Is creativity a type of intelligence?
CHC does not treat creativity as its own broad ability. Idea generation and originality appear as narrow abilities under retrieval fluency (Gr), the speed and ease of pulling ideas from memory. Creativity as people usually mean it (a novel, useful product) also depends on knowledge, motivation, personality and opportunity, which IQ tests don't measure.
The link between IQ and creativity is positive but modest. A meta-analysis by Kim (2005) found a small average correlation between IQ and creativity test scores, roughly 0.17. The popular "threshold hypothesis" says IQ matters for creativity up to about 120 and stops mattering above that. The evidence is mixed. Jauk and colleagues (2013) supported a threshold for some measures of creative potential but not for real-world creative achievement, and results depend heavily on how creativity is measured. A fair summary: higher intelligence helps somewhat, it doesn't guarantee creativity, and claims of a sharp cutoff go beyond the data.
How the types fit together: general intelligence
Every CHC broad ability correlates positively with every other. Carroll's general factor at the top of the model captures that shared variance, and fluid reasoning usually correlates most strongly with it, while processing speed correlates least. This is why an overall IQ predicts outcomes like school performance better than any single ability does, and why specific abilities add only modest information beyond it for most purposes. The g factor explainer covers the debate over what that general factor actually is.
Two popular alternatives sit outside this model. Howard Gardner's theory proposes eight relatively independent intelligences, an idea that has been influential in schools but has little psychometric support; see multiple intelligences theory. Emotional intelligence is a different case: some researchers argue its ability-based version fits within CHC as another broad ability. See IQ vs EQ for that evidence.