How to Understand General Intelligence

General intelligence, also known as g factor, refers to the existence of a broad mental capacity that influences performance on cognitive ability measures. Charles Spearman first described the existence of general intelligence in 1904. According to Spearman, this g factor was responsible for overall performance on mental ability tests. Spearman 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. For example, a person who does well on a verbal test would probably also do well on other tests.

Those who hold this view believe that intelligence can be measured and expressed by a single number, such as an IQ score. The idea is that this underlying general intelligence influences performance on all cognitive tasks.

Charles Spearman was one of the researchers who helped develop a statistical technique known as factor analysis. Factor analysis allows researchers to a number of different test items that can 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.

Spearman believed that general intelligence represented an intelligence factor underlying specific mental abilities. All tasks on intelligence tests, whether they related to verbal or mathematical abilities, were influenced by this underlying g-factor.

Many modern intelligence tests, including the Stanford-Binet, measure some of the cognitive factors that are thought to make up general intelligence. These include visual-spatial processing, quantitative reasoning, knowledge, fluid reasoning, and working memory.

• Visual-spatial processing involves such abilities as putting together puzzles and copying complex shapes.
• Quantitative reasoning involves the capacity to solve problems that involve numbers.
• Knowledge involves a person's understanding of a wide range of topics.
• Fluid reasoning involves the ability to think flexibly and solve problems.
• Working memory involves the use of short-term memory such as being able to repeat a list of items.

The notion that intelligence could be measured and summarized by a single number on an IQ test was controversial during Spearman's time and has remained so over the decades since. 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."

More recently, psychologists such as Howard Gardner have challenged the notion that a single general intelligence can accurately capture all of human mental ability. Gardner instead proposed that different multiple intelligences exist. Each intelligence represents abilities in a certain domain such as visual-spatial intelligence, verbal-linguistic intelligence, and logical-mathematical intelligence.

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.