In the 1880’s, Galton believed that any task or test that a person undertook was influenced by a general ability – their intelligence. He was the first to begin using psychometric testing to measure intelligence. Research by Spearman in 1903, and 1927 led him to agree with Galton’s assertion that a single factor influenced a person’s ability to complete tasks. This factor became known as ‘g’ – general intelligence.

However, not satisfied with this suggestion, Thurstone (1931) expanded the notion of intelligence. Thurstone proposed that intelligence was not a single factor, but was actually several factors that worked in combination. He called these factors the Primary Mental Abilities; vocabulary & comprehension, word fluency, mental arithmetic, memory, perceptual speed, spatial awareness. The major implication of this line of thought was that children should not be assessed for a ‘general intelligence’ as the same child may be good at mental arithmetic, but poor at spatial awareness for example.

For some researchers, these theories were entirely insufficient. The proposals of Galton, Spearman, and Thurstone although in some ways in disagreement with each other, were in other ways similar. They were all considering the relationship between academic abilities. But is this enough to account for human intelligence? Does human intelligence only relate to academic abilities? The theories needed expanding, or rethinking entirely.
In 1983, Howard Gardner proposed a radical new theory of intelligence. Not singular, ‘general intelligence’, but multiple intelligences. Gardner expanded the kinds of factors that should be included when considering what intelligence is. In addition to the academic factors considered previously, he proposed that personal/social skills, musical skills, and physical skills were equally as important and should be considered in any judgement of an individual’s intelligence. This radical departure in thinking raised serious questions about the use of IQ tests as a reliable means of measuring intelligence. Like Gardner, Sternberg (1985) also opted for a wider exploration of what constitutes intelligence. Sternberg considered three alternative factors.

1. Experiential: How fast does a person automate a skill? How soon after learning a new skill (such as driving a car) is the person able to perform that task relatively automatically?
2. Contextual: How quickly is the person able to adapt to their environment?
3. Componential: In what ways does the person process information when solving a problem?

The existing theories on intelligence have produced very little agreement about what intelligence is. But intelligence, whatever its component parts, appears to be our ability to operate in a socio-cultural context – to effectively solve the problems that we encounter in our environment.

Wecshler (1944): “Intelligence is the aggregate or global capacity of the individual to act purposefully, to think rationally, and to deal effectively with his environment”.

Binet & Simon (1916): “..In intelligence there is a fundamental faculty….This faculty is judgement, otherwise called good sense, practical sense, initiative, the faculty of adapting oneself to circumstances. To judge well, to reason well, these are the essential activities of intelligence”.