William Stern

William Stern (1871-1938) was a German psychologist and philosopher and one of the founders of differential psychology, the study of the differences between individuals. Trained in the experimental psychology of the late nineteenth century, he combined empirical research with a philosophy that treated the individual person as the central unit of study. He is best remembered for proposing the intelligence quotient, but his work reached far beyond testing.

He studied philosophy and psychology at the University of Berlin under Hermann Ebbinghaus, earning his doctorate in 1893. He taught at the University of Breslau from 1897 to 1916, then became professor of psychology at the University of Hamburg, where he directed the psychological institute until 1933. With his wife, the psychologist Clara Joseephy, he kept detailed diaries of their three children for many years, material that supported several studies of early childhood, including work on language acquisition. Being Jewish, he was forced out of Germany after the Nazis came to power. He first settled in the Netherlands and then moved to the United States, where he taught at Duke University until his death in 1938.

For intelligence, he proposed dividing a child's mental age by chronological age. Lewis Terman later refined the ratio by multiplying it by one hundred. Stern warned, however, that the score should never be the only way of judging intelligence, since volitional and emotional factors escape any single test. His personalism held that persons, and certain collective entities such as a church or a company, can be understood as living wholes with their own character. Business writer Arie de Geus later drew on this idea.

His influence reaches testing, forensic psychology, where he studied the reliability of eyewitness testimony, and child psychology. He was also the father of the writer and thinker Günther Anders.