Intelligence and Intellectual Development

Modern Conceptions of Intelligence

The modern history of theory and research on intelligence has its twists and turns largely due to the unwieldy nature of the concept. On one hand, intelligence is a concept that has high currency, a valued human resource that people try to cultivate or harness for advancing their causes and agendas, individually or collectively. In the meantime, it is also an abstract, elusive concept with many faces. When a task force put together by the American Psychological Association (APA) reported “knowns and unknowns” about intelligence, it was not able to come up with a uniformly agreed-upon definition of what intelligence is, other than the following statements by Ulrich Neisser:

Three observations can be made about the statements. First, there is some consensus in the research community on what are typically seen as constituents of intelligence or intelligent behaviors; however, there is no clear answer as to whether they are closely connected facets or just concepts loosely coupled together. Second, the statements treat intelligence squarely as a differential or individual difference concept, yet give much leeway for intraindividual and contextual variability. Finally, the statements highlight the term intelligence as a psychological construct, a conceptual tool conjured up by scientists to sort and organize observations at an abstract level, not a physical reality like height or weight.

Although Francis Galton started the tradition of research on psychometric intelligence, Alfred Binet and Charles Spearman were the two most prominent early pioneers of modern theory and measurement of intelligence. Binet, in collaboration with his doctoral student Theodore Simon, developed the first modern intelligence test for the purposes of identifying and helping children with severe learning difficulties in school. Although the purposes were to develop a more reliable and objective assessment than informal clinical observations could offer, Binet saw the instrument as a clinical tool for diagnostic and instructional purposes. He also believed that intelligent performance and behavior involves a set of processes that can be [Page 537]identified in children's performance and targeted for intervention. In comparison with Binet, Spearman was a different kind of researcher. He firmly believed that human intelligence can be clearly defined and measured with accuracy. He used simple measures of sensory discrimination as an indicator of intelligence, believing that sensitivity to subtle differences and relations best characterizes intelligent persons. In contrast to Binet's inclinations as a clinician, Spearman was a mathematician, who preferred numbers to immediate observations. By parsing performance indices into a shared variance and residue variance, he formulated a two-factor theory: individual differences in intelligence can be represented as consisting of a general factor (g) and specific factor (s). When Spearman made a bold claim with a title of “‘General Intelligence’ Objectively Determined and Measured” for his famous 1904 article, Binet was not convinced; he doubted whether a phenomenon as complex as intelligence can be reduced to a single number or a set of numbers. Indeed, he made the counterargument that two individuals who obtain the same score might well use quite different skill sets. Binet was more intrigued by subtle individual differences observed during performance than the apparent simplicity of the mathematical solution offered by Spear-man. This tension, revealed in exchanges between Spearman and Binet and alluded to in the quoted statements above by the APA task force, has lingered to date.

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