What Is General Intelligence (G Factor)?

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Verywell / Emily Roberts

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General intelligence, also known as the general factor or g factor, refers to the existence of a broad mental capacity that influences performance on cognitive ability measures. Other terms such as intelligence, IQ, general cognitive ability, and general mental ability are also used interchangeably to mean the same thing as general intelligence.

This general mental ability is what underlies specific mental skills related to areas such as spatial, numerical, mechanical, and verbal abilities. The idea is that general intelligence influences performance on all cognitive tasks. So, general intelligence can be defined as a construct that is made up of different cognitive abilities. These abilities allow people to acquire knowledge and solve problems.

Spearman's Theory of General Intelligence

Psychologist Charles Spearman helped develop a statistical technique known as factor analysis, which allows researchers to use a number of different test items to measure common abilities. For example, researchers might find that people who score well on questions that measure vocabulary also perform better on questions related to reading comprehension.

In 1904, Spearman suggested that this g factor was responsible for overall performance on mental ability tests. He noted that while people certainly could and often did excel in certain areas, people who did well in one area tended also to do well in other areas.

Spearman's theory of general intelligence is known as the two-factor theory and states that general intelligence or "g" is correlated with specific abilities or "s" to some degree. All tasks on intelligence tests, whether related to verbal or mathematical abilities, were influenced by this underlying g factor.

General intelligence can be compared to athleticism. A person might be a very skilled runner, but this does not necessarily mean that they will also be an excellent figure skater.

However, because this person is athletic and fit, they will probably perform much better on other physical tasks than an individual who is less coordinated and more sedentary.

Types of General Intelligence

In the 1940s, Raymond Cattell theorized that there were two types of intelligence that affect human cognitive ability: fluid intelligence (Gf) and crystallized intelligence (Gc). Fluid intelligence refers to intelligence that we are born with and that we acquire through interacting with our environment. Crystalized intelligence is intelligence that we acquire through our culture.

Others suggest that there are more types of general intelligence, often referred to as the "g's of intelligence." Additional g's of intelligence include:

  • General memory and learning (Gy)
  • Broad visual perception (Gv)
  • Broad auditory perception (Gu)
  • Broad retrieval ability (Gr)
  • Broad cognitive speediness (Gs)
  • Reaction time (Gt)

Components of General Intelligence

There are several key components that are believed to make up general intelligence. These include:

  • Fluid reasoning: This involves the ability to think flexibly and solve problems.
  • Knowledge: This is a person's general understanding of a wide range of topics and can be equated with crystallized intelligence.
  • Quantitative reasoning: This is an individual's capacity to solve problems that involve numbers.
  • Visual-spatial processing: This relates to a person's abilities to interpret and manipulate visual information, such as putting together puzzles and copying complex shapes.
  • Working memory: This involves the use of short-term memory such as being able to repeat a list of items.

How General Intelligence Is Measured

Many modern intelligence tests measure some of the cognitive factors that are thought to make up general intelligence. Such tests propose that intelligence can be measured and expressed by a single number, such as an IQ score.

The Stanford-Binet, which is one of the most popular intelligence tests, aims to measure the g factor. In addition to providing an overall score, the current version of the test also offers a number of score composites as well as subtest scores in ten different areas.

What Do IQ Test Scores Mean?

While scoring systems vary, the average score on many is 100 and the following labels are often used for different scoring ranges:

  • 40 - 54: Moderately impaired or delayed
  • 55 - 69: Mildly impaired or delayed
  • 70 - 79: Borderline impaired or delayed
  • 80 - 89: Low average intelligence
  • 90 - 109: Average
  • 110 - 119: High average
  • 120 - 129: Superior
  • 130 - 144: Gifted or very advanced
  • 145 - 160: Exceptionally gifted or highly advanced

Impact of General Intelligence

While the concept of intelligence is still the subject of debate within psychology, researchers believe that general intelligence is correlated with overall success in life. Some of the effects that it may have on an individual's life include areas such as:

Academic Achievement

One of the most obvious effects of general intelligence is in the realm of academic performance. While intelligence plays a role in academics, there has been a great deal of debate over the extent to which it influences academic achievement.

Research has shown that there is a strong association between general mental ability and academic achievement, but it doesn't act on its own. Some research suggests that between 51% and 75% of achievement cannot be accounted for by the g factor alone.

This means that while general intelligence does affect how well kids do in school, other factors can play a major role.

Job Success

IQ scores have long been thought to correlate to career success. This is why psychological testing has become so prevalent for pre-employment screening and career placement. Many have questioned, however, whether a general mental ability was really more important than specific mental abilities.

A 2020 study published in the Journal of Applied Psychology concluded that both general intelligence and specific mental abilities play an important role in determining career success including income and job attainment.

The importance of the g factor for job success becomes greater as the complexity of the work increases. For occupations with a high degree of complexity, having a higher general intelligence becomes a greater asset.

Health and Longevity

The field of cognitive epidemiology looks at associations between general intelligence and health. Just as health can play a role in influencing intelligence, a person's intelligence may have an impact on their health. Studies have found that high-IQ individuals have a lower risk of:

  • Coronary heart disease
  • Hypertension
  • Obesity
  • Stroke
  • Some cancers

Research has found that people who have higher general intelligence also tend to be healthier and live longer, although the reasons for this are not entirely clear.


Research also suggests that people with higher intelligence scores also tend to earn higher incomes. However, it is important to note that other factors play a mediating role including education, occupation, and socioeconomic background.

While the g factor has a number of effects, other variables are also important. Factors such as socioeconomic status and emotional intelligence, for example, can interact with general intelligence and play a major part in determining a person's success.

Challenges of General Intelligence

The notion that intelligence could be measured and summarized by a single number on an IQ test was controversial, even during Spearman's time. IQ and intelligence testing have remained topics of debate ever since. While influential, the g factor is just one way of thinking about intelligence.

Thurstone's Primary Mental Abilities

Some psychologists, including L.L. Thurstone, challenged the concept of a g-factor. Thurstone instead identified a number of what he referred to as primary mental abilities:

  • Associative memory
  • Number facility
  • Perceptual speed
  • Reasoning
  • Spatial visualization
  • Verbal comprehension

He suggested that all people possess these mental abilities, although to varying degrees. People could be low in some areas and high in others.

Gardner's Multiple Intelligences

More recently, psychologists such as Howard Gardner have argued against the notion that a single general intelligence can accurately capture all of human mental ability. Gardner instead proposed that multiple intelligences exist.

Each intelligence represents abilities in a certain domain such as visual-spatial intelligence, verbal-linguistic intelligence, and logical-mathematical intelligence.

A Word From Verywell

Research today points to an underlying mental ability that contributes to performance on many cognitive tasks. IQ scores, which are designed to measure this general intelligence, are also thought to influence an individual's overall success in life.

However, while IQ can play a role in academic and life success, other factors such as childhood experiences, educational experiences, socioeconomic status, motivation, maturity, and personality also play a critical role in determining overall success.

7 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  3. Tikhomirova T, Malykh A, Malykh S. Predicting academic achievement with cognitive abilities: Cross-sectional study across school educationBehav Sci (Basel). 2020;10(10):158. doi:10.3390/bs10100158

  4. Lang JWB, Kell HJ. General mental ability and specific abilities: Their relative importance for extrinsic career successJournal of Applied Psychology. 2020;105(9):1047-1061.doi:10.1037/apl0000472

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Additional Reading
  • Coon D, Mitterer JO. Introduction to Psychology: Gateways to Mind and Behavior With Concept Maps. Wadsworth; 2010.

  • Myers DG. Psychology, Seventh Edition. Worth Publishers; 2004.

  • Terman LM, Oden MH. Genetic Studies of Genius. Vol. V. The Gifted at Mid-Life: Thirty-Five Years' Follow-Up of the Superior Child. Stanford University Press; 1959.

By Kendra Cherry, MSEd
Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."