The science of intelligence
What is intelligence?
Short answer
Intelligence is a very general mental capability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. That is the definition in a 1994 statement signed by 52 researchers. An IQ score is one way of measuring it with a standardized test, and it leaves things out.
Want your own number? The test is 25 visual puzzles, about 12 minutes, no sign-up.
The research definition
The definition quoted most often comes from a statement called “Mainstream Science on Intelligence.” It was first published in the Wall Street Journal on December 13, 1994, and reprinted in the journal Intelligence in 1997 (Gottfredson, 1997). It describes intelligence as a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience (Gottfredson, 1997).
The statement adds that intelligence is not merely book learning, a narrow academic skill or test-taking smarts. It describes a broader and deeper capability for making sense of your surroundings, for working out what to do (Gottfredson, 1997).
It is worth knowing how the statement was made. Linda Gottfredson sent 131 invitations to sign it and received 100 responses: 52 researchers signed and 48 declined (Gottfredson, 1997). So it reflects the view of a large group of intelligence researchers, not a formal vote of the whole field.
What the statement says about tests
The same statement made several claims about how intelligence relates to test scores:
- Different kinds of intelligence tests all measure the same intelligence. Some use words or numbers, others use shapes or designs (Gottfredson, 1997).
- Intelligence tests do not measure creativity, character or personality, and are not intended to (Gottfredson, 1997).
- A high IQ “no more guarantees success than a low IQ guarantees failure in life” (Gottfredson, 1997).
That is the short version of the difference between intelligence and IQ. Intelligence is the capability. IQ is a score from a standardized test that samples part of it on one day. See is IQ the same as intelligence and how intelligence is measured for the details.
Try one · Pattern Recognition
Which tile comes next?
Tap the option you think is right, or show the answer.
Show the answer
The missing tile shows a very large solid arrow pointing down (option 1).
How to solve it
- Compare neighboring tiles and name what changes each time.
- From tile to tile, the arrow turns a quarter turn clockwise.
- The fill cycles solid, hatched and outline, then starts again.
- Everything else stays the same from tile to tile.
- The last tile shows a very large outlined arrow pointing right. Apply each change once more.
- So the missing tile shows a very large solid arrow pointing down.
That was 1 puzzle. The full test has 25.
The APA task force view (1996)
In 1996 an American Psychological Association task force published “Intelligence: Knowns and Unknowns,” a review of what was and was not known about intelligence (Neisser et al., 1996). It is a useful second reference because it is careful about how much test scores explain:
- IQ scores correlate about .50 with school grades, which accounts for only about 25% of the variance (Neisser et al., 1996).
- They correlate about .55 with total years of education, about 30% of the variance (Neisser et al., 1996).
- Correlations with job performance typically lie between .30 and .50 before correction for unreliability, and tests predict considerably less than half the variance of job-related measures (Neisser et al., 1996).
The task force also noted that even critics of testing do not dispute that scores are stable or that they predict school achievement rather effectively (Neisser et al., 1996). Its overall message: IQ tests measure something real and useful, and most of what makes people differ in grades, careers and lives lies outside the score.
Where g and IQ fit in
In 1904 Charles Spearman proposed a general factor, g, to explain why people who do well on one mental test tend to do well on others (Wikipedia: g factor). In 1963 Raymond Cattell split general ability into fluid intelligence (reasoning with new material) and crystallized intelligence (acquired knowledge) (Wikipedia: Fluid and crystallized intelligence). A full-scale IQ is designed to estimate that general ability. The g factor guide explains the statistics, and theories of intelligence compares g with the broader models.
What the word leaves room for
Everyday speech uses “intelligent” for many things: being wise, creative, socially sharp, or good with your hands. Researchers have tried to formalize some of these as separate intelligences, most famously in Gardner's multiple intelligences. Those ideas are popular, but the evidence for them is much thinner than the evidence for general reasoning ability. Creativity in particular is related to IQ only modestly; see creativity and intelligence.
If you want to see what a reasoning test feels like, our free test gives an estimated IQ from 25 visual puzzles. It samples reasoning, not the whole of what the word intelligence covers.
Sources
- Gottfredson, L. S. (1997). Mainstream science on intelligence: An editorial with 52 signatories, history, and bibliography. Intelligence, 24(1), 13-23. doi.org/10.1016/S0160-2896(97)90011-8
- Neisser, U., Boodoo, G., Bouchard, T. J., Jr., Boykin, A. W., Brody, N., Ceci, S. J., Halpern, D. F., Loehlin, J. C., Perloff, R., Sternberg, R. J., & Urbina, S. (1996). Intelligence: Knowns and unknowns. American Psychologist, 51(2), 77-101. doi.org/10.1037/0003-066X.51.2.77
- g factor (psychometrics). Wikipedia. en.wikipedia.org/wiki/G_factor_(psychometrics)
- Fluid and crystallized intelligence. Wikipedia. en.wikipedia.org/wiki/Fluid_and_crystallized_intelligence