There is no Unique Theory of Intelligence

Theory of IntelligenceThis page deepens into Theory of Intelligence. We will talk about how psychologists approached the meaning of intelligence and developed their theories. We will also see briefly some of the most important theories of intelligence.


Although, psychologists have agreed on that the key to understanding intelligence is the ability of the environment adaptation, scholars still don’t agree with a single Theory of Intelligence.


There are groups of researchers that study intelligence using psychometric tests and analyzing the results. Others believe that intelligence draws upon many other abilities that are not measurable by tests. Recently, psychologists tried to explain intelligence using a biological point of view.


Some of the most prominent theories of intelligence follow:


General Intelligence


In 1904, Charles Spearman proposed the first theory of intelligence. Spearman said that there is a general mental capability, symbolized by letter g, which represents Intelligence. This factor determines the performance in all intellectual tasks.


Intelligence: A Very Short Introduction
Intelligence: A Very Short Introduction

His conclusions resulted when he noticed that people who performed well on a mental-ability test tended to do also well on other tests. On the other hand, people who performed poorly on a test also tended to perform poorly on others.


Numerous researchers based on this theory of intelligence and developed new ones. Some of them follow.


Primary Mental Abilities


In 1938, Louis L. Thurstone proposed the Primary Mental Abilities theory. This theory suggests that the human intelligence is constituted by seven independent primary mental abilities. These are the following:

o Verbal Comprehension

o Verbal Fluency

o Number or Arithmetic Ability

o Memory

o Perceptual Speed

o Inductive Reasoning

o Spatial Visualization


Thurstone identified the above abilities after creating a set of 56 tests. His wife Thelma helped him to create this test set. Then they administered this test set to 240 college students and from the results analysis, Thurstone developed the Primary Mental Abilities theory.


Fluid and crystallized intelligence


In 1966, Raymond B. Cattell and John Horn developed the Fluid and Crystallized Intelligence theory. That is, Intelligence consists of two parts, the fluid intelligence and the crystallized intelligence.


The fluid is the biological aspect of intelligence and it is measured by calculating the speed of reasoning and memory capacity. Also, it is increased into adulthood and decreased with aging.


The crystallized intelligence is the expansion skill through learning and experience. The sources of new knowledge and new experiences are unlimited, so this type increases unlimitedly over time.


Multiple Intelligences


This theory proposed from Howard Gardner in 1983. He concluded that there were seven different types of intelligence. These are:

Multiple Intelligences : The Complete MI Book
Multiple Intelligences : The Complete MI Book

o Linguistic

o Musical

o Logical-Mathematical

o Spatial

o Bodily-Kinesthetic

o Intrapersonal

o Interpersonal


In the late 1990s, Gardner added one new type of intelligence, the naturalist, which was the ability in recognizing plants, animals, and minerals.


Gardner based his research not so much in analyzing psychometric tests, but in studying strange cases such as, people who had lost a mental ability and improved another,  people who excelled in a skill but not in others, and people who developed their skills in the absence of others. He concluded that there must be multiple independent bits of intelligence that explain the strange cases that he studied. He came up with the “Theory of Multiple Intelligences.”


He also identified a renowned personality, with high mental performance, for each intelligence type.He distinguished the following people:

linguistic Intelligence – The poet T.S Eliot

Musical Intelligence – The composer Igor Stravinsky

Logical – Mathematical – The physicist Albert Einstein

Spatial – The painter Pablo Picasso

bodily-kinesthetic – The dancer and choreographer Martha Graham

Intrapersonal – The leader Mohandas Gandhi

Interpersonal – The psychiatrist Sigmund Freud

Naturalist – The naturalist Charles Darwin.


Triarchic Theory of Intelligence

In 1985, Robert Sternberg formed the Triarchic Theory of Intelligence. Sternberg said that intelligence is divided into three major skills.  Let’s see them below:


o Analytic intelligence

o Creative intelligence

o Practical intelligence


The main difference of the Sternberg’s Triarchic Theory of Intelligence from the theory of multiple intelligences is that the three parts relate each other and are divisions of a bigger single entity.


The Analytic draws on the basic cognitive processes. It is the ability to reason, to process information and to solve problems. Also, it is the skill that resembles more with the general concept of intelligence.


The Creative is the ability to use past experiences and learn from them to deal with new situations in the future.


Sternberg noticed that the psychometric tests were unable to measure the creative intelligence because people who had scored high on such trials, faced difficulties in dealing real life situations.


The practical skill is the people’s adaptation ability to the environment. This seems like the modern definition of intelligence.


People, who can adapt to and manipulate their environment to create the appropriate situations according to their needs, have a tendency to be successful in real world situations. Sternberg also noticed that high practical intelligence does not necessarily mean high scores in IQ tests.


Biological Research on Intelligence


The Psychometric theories approach intelligence based on hypothetical mental constructs. Biological studies are not based on such hypothesis.


Followers of these theories also called reductionists, believe that the way to understand the nature of intelligence is by identifying the biological processes behind it.


The conclusions of biology should be used together with the psychometric theories to construct a single Theory of Intelligence.


Hemispheric Research


The Psychologist Jerre Levy and others found that the brain hemispheres are responsible for different processes. The left hemisphere is engaged with analytical thinking and problem solving while the right hemisphere handles visual and spatial tasks.


Brain wave studies


Another topic that Biologists are researching is the brain wave activity. There are studies in this field that examine the brain waves of patients while they perform mental activities. For example, the psychologist Hans Eysenck studied the brain wave patterns in subjects who were taking an intelligence test.


Some studies suggested that there is a relation between EEG (Electroencephalogram) waves, ERP (Event-Related-Potential) waves and the results of intelligence tests.


Blood-flow Research


This kind of study is more recent and focuses on the measurement of the brain’s blood flow. As Blood-flow is a sign of brain activity, these measurements take place in patients that are performing cognitive tasks.


One interesting result is that patients who performed well on intelligence tests had an overall decreased brain blood flow than others who didn’t perform as well. These conclusions resulted from psychologist Richard Haier using a Positron Emission Tomography (PET).


Also, psychologist John Horn found that older adults showed a decreased blood flow in some brain areas such as areas responsible for concentration.




intelligence, human. (2009). Encyclopdia Britannica. Encyclopdia Britannica 2009 Student and Home Edition. Chicago: Encyclopdia Britannica.


Detterman, Douglas K. “Intelligence.” Microsoft Student 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008.




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3 comments on “There is no Unique Theory of Intelligence

    • Yes I know. That’s why all the sources are mentioned in the end of the article that you obviously didn’t read…

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