Spearman's Bifactorial Theory of Intelligence

Spearman is one of the most important figures in the study of intelligence. His approach was a real revolution, and, in his theory of intelligence, he made us start to question whether intelligence was a single and indivisible factor.
Spearman's Bifactorial Theory of Intelligence

Last update: 08 December, 2020

When speaking about intelligence and its scientific study, we have to mention Charles Spearman. His studies provided a great deal of information and ideas for those who came after him. Why was, and is, Spearman’s theory of intelligence (also called the bifactorial or two-factor theory) so important for the research into intelligence and psychometric testing?

Over the last few two hundred years, many different thinkers have studied and scientifically conceptualized intelligence. Among them is Charles Spearman. He coined the term “general intelligence” in 1904 after studying the works of Francis Galton.

Charles Spearman (1863-1945) was a psychologist who was born in London. He was a disciple of the father of experimental psychology, Wilhelm Wundt (1832-1920), and influenced by the works of Francis Galton (1822-1911).

He was the founder of the London School of Psychology at the University College of London (UCL). There, along with many of his students, he put experimental psychology into practice during the first decades of the 20th century.

Spearman’s bifactorial theory of intelligence

Spearman’s bifactorial theory proposes a system where intelligence is broken down into two factors. He named them the general factor (g) and the specific factor (s).

Spearman affirmed in 1923, with his bifactorial theory of intelligence, that the academic performance of some school-age children correlated with the results they obtained in some sensory tests that he himself chose and applied to them.

Thus, he concluded that it was possible to measure general intelligence by using the capacity for sensory discrimination, as Galton had previously proposed.

Within the current scientific study of intelligence, it’s hard to approach the subject without referring to Spearman’s two-factor theory. The truth is that this theory laid the foundations for a whole new study approach.

Heads made of trees.

General intelligence

Spearman defined general intelligence as “the ability to infer relationships and, from them, to make correlations“.

He also spoke of a neural phenomenon (g). He considered this to be a potential source of energy in the brain. In addition to that, he postulated that this energy differed quantitatively between individuals and would be determined genetically. (Spearman 1927 pp. 124, mentioned by Rosa María Bonastre Rovira in “La inteligencia general (g), la eficiencia y el índice velocidad de conducción nerviosa: una aproximación empírica, 2004″).

This refers to a part of our intelligence that intervenes in many activities, but which doesn’t specialize in any of them. This is in contrast to the specific actors or “s-factors”, which do specialize.

The specific factors

Also known as s-factors, these are the factors that would correspond to different abilities. Among them, we find mechanical, verbal, numerical, and spatial activities.

Therefore, Spearman’s bifactorial theory of intelligence tells us that if a school-aged child has good grades in one subject, then they’ll be more likely to get good grades in the rest of them as well.

This is because general intelligence or “g” is involved in these evaluations. However, this doesn’t guarantee that the child will excel in any specific skill, discipline, or area in the future. Why? Because the intervention of these so-called s-factors is necessary in order for this to occur.

Contributions to the study of intelligence

From Spearman’s bifactorial theory and the different analyses it received, other ideas emerged to try to scientifically understand the phenomenon of intelligence.

Some of these criticisms were related to cultural bias, financial factors, the geographical location of the subject’s home, or their academic level. Since Spearman’s bifactorial theory doesn’t take these factors into account, and genetics can’t explain everything, new proposals and models emerged.

Other definitions

Some other definitions that have seemed relevant over time are from the following thinkers:

  • Hebb D. O. (“The organization of behavior”, 1949). He affirms that “Intelligence is the potential of an animal organism to learn and to adapt to its environment“.
  • Stemberg (“Beyond IQ: A triarchic theory of human intelligence”, 1985). He defines it as follows: “Intelligence explains the differences we observe between people in order to solve problems“.
  • Gottfredson L. S. (“Why g matters: The complexity of everyday life”, 1997). He states that intelligence “Is a very general mental faculty that, among other things, implies the ability to react, plan, solve problems, think abstractly, understand complex ideas, learn quickly, and learn from experience“.
  • Howard Gardner. (“The prefrontal cortex: Executive and cognitive functions”, 1999) recognizes intelligence as “A biopsychological potential for processing information in order to solve problems or create valuable products for a given culture or community“.

These are some of the most important studies of intelligence, and, as we can see, they’re related to conflict resolution and adapting to the environment. This shows that current thinkers no longer take into account only the subjects’ genetic conditions.

A brain.

Applications in psychology

In psychology, there are psychometric intelligence tests in almost all areas that have aroused interest. Spearman’s bifactorial theory, although not valued by some, is of great relevance. From his studies, other studies emerged that were starting to shape the different psychometric intelligence tests that we use today.

Nowadays, we still administer psychometric tests based on Spearman’s bifactorial theory. Three examples of this are Raven’s Progressive Matrices Test, D-48 Domino Test, and Cattell’s G-factor test.

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