Our maverick of philosophic theoreticians, Stern, combined the philosophical and scientific approach to examine human nature. This made a major contribution to the early science of psychology. Indeed, Stern was perhaps the first theoretician to describe ways of combining physical and mental studies in order to describe the "total human individual".

His interest in individual differences led to the development of the concept, "intelligence quotient (IQ)". (A concept, it may be noted, that was later mathematically operationalized by Terman).

Stern's revolutionary notion was elegantly simple. It involved the division of a child's measured mental age by their chronological age to achieve a relative intelligence score. This idea has stuck ever since, at least in a modified form with the notion of 'deviation quotient' proposed by Wechsler.

Did you know? The introduction of psychological testimony as "expert opinion" is due in part to Stern's research.