ABSTRACT
The study of individual differences has always formed an important part of experimental psychology, ever since the early days of Sir Francis Galton; even Wundt, who is often represented as being inimical to the study of individual differences, made an important contribution to the description of personality by suggesting the transformation of the traditional Greek typology of the four temperaments into a two-dimensional system closely resembling that later on advocated by this author. In spite of this early inclusion of personality variable into Wundt’s system of physiological psychology, the paths of experimental psychology (in the narrow sense) and of the study of individual differences have tended to diverge. Cronbach (1957), in his Presidential Address to the American Psychological Society, pointed out that there were two disciplines of scientific psychology and that psychology would be unlikely to prosper unless they could be brought together into one integrated whole. This hope, strongly supported in my writings (Eysenck, 1967), has only been fulfilled very partially; in spite of much lip service, experimentalists and psychometrics have tended to go their own way, and integration is still in the future.
