Intelligence

During recent history, intelligence has been one of the most polemic concepts in psychology. Major controversies in intelligence include the specific contribution of biological and cultural factors to intelligence, the unity or diversity of intelligence, the measure of intelligence, the potential intellectual differences among human groups, the intelligence changes across life span, the potential differences in the patterns of intellectual abilities between men and women, animal intelligence, and artificial intelligence. All these questions remain at least partially controversial. This entry discusses how intelligence is interpreted and measured, the theory of multiple intelligences, intelligence test [Page 921]performance, and a summary of what is known and unknown about intelligence.

The term intelligence derives from the Latin word intelligentia that means comprehend or perceive. This term was widely used in philosophy during the last centuries and became a cornerstone in 20th-century psychology. Intelligence has been defined in different ways. David Wechsler, one of the major authorities in the area, in 1944 presented a quite compressive definition of intelligence: “Intelligence is the aggregate or global capacity of the individual to act purposefully, to think rationally and to deal effectively with his environment” (p. 3). This definition contains one of the major controversial issues in intelligence: Is intelligence a global capacity, or the aggregate of different abilities? Clearly, two different interpretations of intelligence can be postulated: (1) There is a general intelligence factor that potentially may be measured and even quantified, and (2) there are different forms of intelligence, not a single one. This definition also contains a fundamental idea in intelligence: intelligence includes not only a behavioral dimension (“to act”) but also an internal dimension (“to think”).

Charles Spearman supported the first interpretation of intelligence, that is, there is a general intelligence factor. He postulated a two-factor theory of intelligence: Any intellectual test measures both a g factor common to all other cognitive tests and a specific (s) factor unique to that particular test. The relation between g and s components can be different, but g is always included in any cognitive tests. The existence of this general intelligence g factor represents the theoretical basis to assume that intelligence can be quantitatively measured using a single compound score (intelligence quotient, IQ).

Louis Leon Thurstone was a major supporter of the second interpretation of intelligence, that is, there are different forms of intelligence. He used factor analysis to find the fundamental intellectual abilities. He concluded that there are a relatively limited number of factors that would correspond to the fundamental or primary mental abilities: space, verbal comprehension, word fluency, induction, perceptual speed, deduction, rote learning, and reasoning. He further proposed that each factor corresponds to certain specific nervous system activity. Later, Raymond Cattell proposed that more than one second-order analysis factor could be found. He distinguished between “fluid intelligence” (corresponding to and reflecting a pattern of neurophysiological and incidental learning influences) and “crystalized intelligence” (highly sensitive to each person’s unique cultural, educational, and environmental experiences). This distinction rapidly became quite popular in psychology.

During recent years, intelligence has been partially equated with executive functions, understood as a set of cognitive processes including but not limited to attentional control, reasoning, metacognition, problem solving, working memory, behavioral temporality, and inhibitory control.

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