An abstract concept whose definition continually evolves and often depends upon current social values as much as scientific ideas. Modern definitions refer to a variety of mental capabilities, including the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, understand others, and learn from experience as well as the potential to do so.

Several theories about intelligence evolved in the twentieth and twenty-first centuries including the idea of multiple types of intelligence (e.g., emotional intelligence). With each new theory, debate occurs about the nature of intelligence and whether it is strongly hereditary or strongly environmental or a mixture of both. The measurement of social psychology traits such as personality, abilities, knowledge, attitudes, and intelligence is known as psychometrics. Debate has arisen over how accurately intelligence can be measured using psychometric techniques. Publication of The Bell Curve by Richard J. Herrnstein and Charles Murray in 1994 stirred the controversy in this area. Their findings pointed to links between social class, race, and IQ scores. Others questioned the cultural bias IQ and similar tests, suggesting that environment and cultural bias affect the measurement of intelligence or a predictor of achievement and success and thus affected Herrnstein and Murray's results.

Part of the debate about intelligence stems from the fact that nobody has adequately defined what intelligence really means. In everyday life, there is a general understanding that some people are “smart,” but when social scientists and psychologists try to define “smart” precisely, they often have difficulty because a person can be gifted in one area and average or below in another. To explain this phenomenon, some psychologists have developed theories to include multiple components of intelligence.

Charles Darwin's younger cousin, Sir Francis Galton, inspired by the Origin of the Species, developed a forerunner of twentieth-century intelligence testing in the 1860s when he set out to prove that intelligence was inherited. He used quantitative studies of prominent individuals and their families.

British psychologist and statistician Charles Spearman in 1904 introduced a central concept of intelligence psychometrics, pointing out that people who perform well on one type of intelligence test tend to do well on others also. This general mental ability that carried over from one type of cognitive testing to another, Spearman named g—for general intelligence. Spearman concluded that g consisted mainly of the ability to infer relationships based on one's experiences. Spearman's work led to the idea that intelligence is focused on a single, main component.

With the adoption of widespread testing using the Stanford-Binet test and two versions created for the Army in World War I, the concept of the intelligence test departed from Binet and Simon's initial view. Intelligence became associated with a fixed, innate, hereditary value. That is, one's intelligence, as revealed by IQ tests, was locked at a certain level because of what was believed to be its hereditary basis. Although a number of well-known and respected psychologists objected to this characterization of intelligence, it gained popularity, especially among the public.

At this time, people placed great faith in the role of science in improving society; intelligence tests were seen as a specific application of science that could be used beneficially. Unfortunately, because of the nature of the tests and because of many people's willingness to accept test results uncritically, people of racial minorities and certain ethnic groups were deemed to be genetically inferior with regard to intelligence compared to the majority.

Some early psychologists thought that measuring the speed of sensory processes and reaction times might indicate an individual's intelligence. This approach provided no useful results. Subsequently, tests reflecting white American culture and its values provided the benchmark for assessing intelligence. Although such tests indicate the degree of academic success that an individual is likely to experience, many have questioned the link to the abstract notion of intelligence, which extends beyond academic areas.

Immigration laws restricted entry into the United States of “inferior” groups, based on the results of early intelligence testing, according to some scholars. This claim seems to have some merit, although many psychologists objected to the conclusions that resulted from mass intelligence testing. In large part, the immigration laws seemed to reflect the attitudes of Americans in general regarding certain groups of people rather than specific views about intelligence and the value of intelligence testing.

In the 1940s, a different view of intelligence emerged. Rejecting Spearman's emphasis on g, American psychologist L.L. Thurstone suggested that intelligence consists of specific abilities. He identified seven primary intellectual abilities: word fluency, verbal comprehension, spatial ability, perceptual speed, numerical ability, inductive reasoning, and memory.

Taking Thurstone's concept even further, J.P. Guilford developed the theory that intelligence consists of as many as five different operations or processes (evaluation, convergent production, divergent production, memory, and cognition), five different types of content (visual, auditory, symbolic, semantic, and behavioral) and six different products (units, classes, relations, systems, transformation, and implications). Each of these different components was seen as independent; the result being an intelligence theory that consisted of 150 different elements.

In recent past, psychologists have expanded the notion of what constitutes intelligence. Newer definitions of intelligence encompass more diverse aspects of thought and reasoning. For example, psychologist Robert Sternberg developed a three-part theory of intelligence that states that behaviors must be viewed within the context of a particular culture (i.e., in some cultures, a given behavior might be highly regarded whereas in another, the same behavior is given low regard); that a person's experiences impact the expression of intelligence; and that certain cognitive processes control all intelligent behavior. When all these aspects of intelligence are viewed together, how people use their intelligence becomes more important than the question of “how much” intelligence a person has. Sternberg has suggested that current intelligence tests focus too much on what a person has already learned rather than on how well a person acquires new skills or knowledge. Another multifaceted approach to intelligence is Howard Gardner's proposal that people have eight intelligences: logical-mathematical, linguistic, musical, spatial, bodily-kinesthetic, interpersonal, intrapersonal, and the naturalistic. Daniel Goleman has written about an emotional intelligence of how people manage their feelings, interact and communicate, combining the interpersonal and intrapersonal of Gardner's eight intelligences.

One feature that characterizes the developing concept of intelligence is that it has broader meaning than a single underlying trait (e.g., Spearman's g). Sternberg and Gardner's ideas suggest that any simple attempt at defining intelligence is inadequate given the wide variety of skills, abilities, and potential that people manifest.

The current approach to intelligence involves how people use the information they possess, and how they can learn new things, not merely the knowledge they have acquired. Intelligence is not a concrete and objective entity, although psychologists have used various psychometric techniques in attempts to assess it. The particular definition of intelligence that has currency at any given time reflects the social values of the time as much as the scientific ideas.

The approach to intelligence testing, however, remains closely tied to Charles Spearman's ideas, despite new waves of thinking. Tests of intelligence tend to mirror the values of American culture, linking them to academic skills such as verbal and mathematical ability, although performance-oriented tests exist.

See also Culture-fair test ; Jensen, Arthur; Nature-nurture controversy ; Stanford-Binet Intelligence Scales ; Wechsler Intelligence Scales .



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Goleman, Daniel, Lisa Bennett, and Zenobia Barlow. Ecoliterate: How Educators Are Cultivating Emotional, Social, and Ecological Intelligence. San Francisco, CA: Jossey-Bass, 2012


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