Functional psychology was less a system than an attitude that valued the utility of psychological inquiry. Assuming a philosophical underpinning from the pragmatism of William James and Charles Sanders Peirce, functional psychology fit well into the pioneering spirit of America. From its beginning, functional psychology had a clear emphasis on applying psychology to individual and social improvement, as was evident from the works of Münsterberg, McDougall, and Hall. The tradition of British natural science and evolutionary theory was integrated into psychology in the views on adaptation championed by the Chicago functionalists, such as Dewey, Angell, and Carr. Mental testing and the study of human capacity constituted important areas of investigation among the Columbia functionalists, represented by Cattell, Thorndike, and Woodworth. Although its reaction to structural psychology kept functional psychology from developing a systematic alternative model of psychological inquiry, this phase of American psychology resulted in two critical benefits. First, functionalism firmly entrenched the new science of psychology in America and imposed on it a particular American orientation toward applied psychology. Second, functional psychology provided a necessary transition from the restricted context of structural psychology to more viable models of psychology, permitting the science to progress.

In this chapter, I review the history of psychological accounts of intelligence in the nineteenth and twentieth centuries. I open with an account of the thinking of Galton and Binet. Although Binet is often viewed as atheoretical, I show this not to be the case at all. I then discuss some of their successors, including Spearman, Thomson, Holzinger, Thurstone, Guilford, Guttman, Burt, Vernon, Cattell, Carroll, and Johnson and Bouchard.