Conceptual foundations of IQ testing.

Abstract

Cognitive neuroscience has not yet arrived at a definition of what human intelligence is. is a chapter-heading word used in the 19th century to denote some unspecified mental property that increases in evolution. Other words were given speculative evolutionary meanings in the 19th century: retardation. When the Binet-Simon test came along as a test to screen degrees of mental retardation, later as a pupil classification instrument, some (not Binet) associated the test with these 19th-century words and meanings. Descendants of the Binet-Simon instrument, IQ tests, remain useful today, but the old legendry lives on with them, at times supporting speculative social and political arguments. Researchers need to disentangle what is factual about IQ testing from its associated legendry. The intelligence that the IQ test is supposed to test has never been defined in precise scientific terms and there is no evidence from cognitive neuroscience to indicate that it can be. Many words in the English language—e.g., intelligent, courageous, hard-working, thoughtful—are useful in denoting differences between people even though the properties suggested by the words cannot be traced back to simple and distinct processes at the physiological level. The belief that there is a unitary human property of intelligence— and that it can be measured—arose at the turn of the 20th century. What brought it to life was not the findings of scientific research but, first, speculative efforts to account for human differences in evolutionary terms and, second, the invention of a practically useful school readiness test. Before the turn of the 20th century, words denoting properties of people—intel ligence, genius, degeneracy, retardation— were given speculative evolutionary meanings. These interpretations all together formed what one might call a cloud of legendry. When, in the first decade of the 20th century, Binet and Simon put forward a useful Measuring Scale of Intelligence for ascertaining children's readiness for school, the cloud of legendry descended around the test. In the 20th century, IQ test data have been given social and political interpretations that owe much to the legendry and very little to scientific information about what the IQ test is and does. Researchers know enough today to disentangle the scientifically and psychometrically meaningful part of IQ testing from the cloud of legendry, and they should proceed to do just that. The conceptual foundations of IQ testing, the words and ideas to be embodied in speculations about what the tests might mean in evolutionary terms, were established well before the tests were invented. In the 19th century, scientists often connected their work to everyday life by attaching scientific meanings to ordinary words. C. S. Peirce used to argue it was a mistake to do this. Invent neologisms, he said. Otherwise, words' traditional meanings contaminate and confuse your thinking about the scientific phenomena. But scientists, including