Charles Spearman’s Theory of Intelligence Explained


Intelligence has always been an important component in the study of psychology. Intelligence impacts how an individual can be successful in life, establish relationships, or learn new awareness skills. We have different types of intelligence that we recognize today, but it was Charles Spearman who brought science into the study of intelligence.

Intelligence is defined as an ability to obtain, and then use, knowledge in a way that is productive. It’s a concept that has been known throughout all of civilized human history, but one that has not always been scientifically understood from a psychological standpoint. Intelligence was often considered to be a philosophical concept. Spearman wanted to bring the scientific method to intelligence.

How do some people grow up to be great thinkers? Why are some people great learners? And why do some people struggle to grasp even the simplest of concepts? Through observation and measurement, the theory of intelligence was born.

Who Was Charles Spearman?

Born in 1863, Charles Spearman served in the military for 15 years before pursuing a doctorate in experimental psychology. He didn’t begin his advanced academic studies until he was nearly 40 years old. It would take him 9 years to earn his PhD, having been recalled to the military to serve in the Second Boer War.

Spearman actually published his theory of intelligence two years before he earned his doctorate degree in experimental psychology.

Determining General Intelligence from a Scientific Standpoint

Spearman developed a statistical procedure that he hoped would be able to shed some insight into the psychology of intelligence. The process was called “factor analysis.” In this procedure, related variables would be tested for correlation with each other. Then those correlations would be evaluated to find clusters or groups of information within the variables. This would help Spearman be able to identify specific types of intelligence.

In the initial factor analysis procedures, Spearman looked at how good people performed while completing various tasks. He included tasks such as perceiving weight, identifying color, following directions, completing mathematics, and distinguishing pitch. Each person who took the tests would have specific data points generated based on their performance.

When Spearman went back through the data, he noticed that people who did well in one area of the factor analysis test would also score higher in all other areas as well compared to those who did not perform well in one area. This led Spearman to the conclusion that would lead to the theory of intelligence: that there must be one central factor that influences the cognitive abilities of each individual.

It should be noted that much of the statistical work that Spearman used to develop his theory of intelligence came from the work of Francis Galton. Galton is credited with developing correlation, which would be the primary statistical tool that Spearman would use to create his theory.

What Is “G Factor” and Why Is It Important?

Spearman identified what he called the “g” of intelligence. This G-factor would become the general intelligence that a person had. This means anyone who can perform well on one test should be able to perform well on other tests because of their generalized intelligence.

This means that the G-factor can also be measured. An intelligence quotient score from an IQ test would be a reflection of this capability. The higher a person scores on this test, then the better their general intelligence is going to be.

What is notable about this observation is that a person cannot be trained to have a higher G-factor. It is a part of who they are. Or as Spearman described it in his paper:

G is in the normal course of events determined innately. A person can no more be trained to have it in higher degree than he can be trained to be taller.

So let’s think about intelligence like this. Imagine you get to meet Usain Bolt. He’s incredibly gifted in the ability to run 100 meters and has won Olympic gold medals and numerous international championships. In this specific track and field event, Bolt is one of the consistently best people in the world. Put the average person up against him and you’re probably going to lose the race.

But now let’s take Usain Bolt out of his element. Let’s put him into a swimming pool and tell him he needs to compete in a 100-meter swimming event. Is he going to be just as good as he is on the racing track in that event? Probably not. Usain Bolt isn’t Michael Phelps. Yet because of his athleticism and consistent training, Bolt would still likely perform better than the average person dropped into a swimming pool and asked to compete.

Michael Phelps would probably destroy Usain Bolt in swimming, just like Bolt would destroy Phelps in racing. Yet both are incredibly dominant in their specialization and that dominance would make them better than the average person taken from the street because they are more athletic than a person selected at random.

This is what Spearman brought to the study of intelligence. He believed that there was an intelligence factor underlying the specific abilities that a person was able to achieve. Any achievable measurement from any test would be influenced by the G-factor of that individual.

How Accurate Is the Theory of Intelligence?

Charles Speaman’s theory of intelligence was controversial at the time it was proposed and it is still hotly debated to this day. The idea that general intelligence can be measured and classified for comparative purposes has often been challenged. Psychologists like L.L. Thurstone believe that it would be more accurate to say that people have primary mental abilities instead of a G-factor.

Instead of having just one generalized intelligence, the counter to Spearman’s theory is that different multiple intelligences exist in individuals. Each intelligence would represent a specific ability that could be measured. From linguistic skills to pitch recognition to visual interpretation, each measurement would provide more specific information about an individual’s intelligence. To reach a generalized intelligence number, one could then average the results of each individualized test.

Spearman recognized over time that general intelligence wasn’t a single ability, but a two-factor ability that worked closely together. He dubbed these abilities to be eductive and reproductive.

At the end of the day, even after all of the statistics and equations, Spearman also noted that every person is a genius at something. That genius just hasn’t always been discovered. He felt that testing could help point people in the right direction, which is how we use our standardized tests today.

Intelligence testing isn’t a judgment. It is a guide or a reference tool to help people consider their options. Every person has something unique to contribute and ultimately no IQ score can determine what that contribution will be.