Sure, intelligence is a collection of cognitive abilities, but a unifying construct called “intelligence” that can be measured and quantified must exist, right? Psychologists have developed intelligence tests and worked with militaries, schools, and corporations, trying to sort individual differences in intelligence in the service of job selection, academic honors, and promotions. From all this testing has emerged the concept of “g” as a general and measurable intelligence factor.
The g-factor is comprised of subcomponents known as s-factors. Together, the g- and s-factors comprise what is called the two-factor theory of intelligence:
  • g-factor: Some psychologist comes up with a test of mental abilities and gives it to a lot of people. When a score is calculated and averaged across abilities, a general intelligence factor is established. It is meant to represent how generally intelligent you are based on your performance on this type of intelligence test.
  • s-factor: The individual scores on each of the specific ability tests represent the s-factors. An s-factor score represents a person’s ability within one particular area. Put all the s-factors together, and you get the g-factor. Commonly measured s-factors of intelligence include memory, attention and concentration, verbal comprehension, vocabulary, spatial skills, and abstract reasoning.
In a related theory, psychologist and intelligence research pioneer Louis Thurston (1887–1955) came up with a theory of intelligence called primary mental abilities. It’s basically the same concept as the s-factor part of the two-factor theory, with a little more detail. For Thurston, intelligence is represented by an individual’s different levels of performance in seven areas: verbal comprehension, word fluency, number, memory, space, perceptual speed, and reasoning.

A closer look at the g factor

Psychologists continue to divide general intelligence into specific factors. The Cattell-Horn-Carroll Theory of Cognitive Abilities (CHC Theory) proposes that “g” is comprised of multiple cognitive abilities that when taken as a whole produce “g.” Early work by the individual contributors to CHC theory, Raymond Cattell, John Horn, and John Carroll, converged to produce a model of general intelligence consisting of ten strata. They are as follows:
  • Crystallized intelligence (Gc): comprehensive and acquired knowledge
  • Fluid intelligence: reason and problem-solving abilities
  • Quantitative reasoning: quantitative and numerical ability
  • Reading and writing ability: reading and writing
  • Short-term memory: immediate memory
  • Long-term storage and retrieval: long-term memory
  • Visual processing: analysis and use of visual information
  • Auditory processing: analysis and use of auditory information
  • Processing speed: thinking fast and automatically
  • Decision and reaction speed: coming to a decision and reacting swiftly
Researchers continue to work with the CHC model and have developed research programs looking into adding to the 10 strata. Many professionals believe that sensory and motor abilities need to be more fully included in this theory, and researchers are looking at “tentative” factors such as tactile abilities (touch), kinesthetic ability (movement), olfactory ability (sense of smell), and psychomotor ability and speed.

The street smarts component of intelligence

Robert Sternberg developed the triarchic theory of intelligence in part to address the street smarts controversy, which holds that many intelligent people may be smart when it comes to academics or in the classroom but lack common sense in real life or practical matters. The three intelligence components of his theory are as follows:
  • Componential: Componential intelligence depends on the same factors measured by traditional intelligence tests (memory, verbal fluency, and so on). This is the book smarts aspect of intelligence. Sternberg emphasized that these abilities are often disconnected from ordinary life, issues, and problems. Einstein seemed to have possessed this component.
  • Experiential: Experiential intelligence encompasses the ability to deal with two different types of problems: new problems and routine problems. It requires the ability to recognize new problems, as opposed to everyday problems; search for and generate solutions; and implement solutions.
  • Contextual: Contextual intelligence is a type of practical intelligence that allows people to go about their daily lives without walking in front of cars, telling police officers to get lost, or letting the trash pile up to the ceiling. This is the street smarts aspect of intelligence that psychologists sometimes seem to lack in the eyes of their clients.

Multiple intelligences

Gardener generated a theory known as multiple intelligences from observing extremely talented and gifted people. He came up with seven types of intelligence that are typically left out of conventional theories about intelligence: