William Sheldon, (born November 19, 1898, Warwick, Rhode Island, U.S.—died September 16, 1977, Cambridge, Massachusetts), American psychologist and physician who was best known for his theory associating physique, personality, and delinquency.
Sheldon attended the University of Chicago, where he received a Ph.D. in psychology in 1926 and an M.D. in 1933. In 1951, after having worked at various universities, Sheldon joined the University of Oregon Medical School, where he became distinguished professor of medicine and director of the constitution clinic, which examined the relationships between physical characteristics and disease; he remained there until his retirement in 1970. Also in 1951 he became director of research at the Biological Humanics Foundation in Cambridge, Massachusetts.
Influenced by the pragmatism of American philosopher and psychologist William James and by his background as a naturalist who had also studied animals, Sheldon became convinced that the psychological makeup of humans had biological foundations. He constructed a classification system that associated physiology and psychology, which he outlined in The Varieties of Human Physique (1940) and The Varieties of Temperament (1942). Sheldon classified people according to three body types: endomorphs, who are rounded and soft, were said to have a tendency toward a “viscerotonic” personality (i.e., relaxed, comfortable, extroverted); mesomorphs, who are square and muscular, were said to have a tendency toward a “somotonic” personality (i.e., active, dynamic, assertive, aggressive); and ectomorphs, who are thin and fine-boned, were said to have a tendency toward a “cerebrotonic” personality (i.e., introverted, thoughtful, inhibited, sensitive). He later used this classification system to explain delinquent behaviour, finding that delinquents were likely to be high in mesomorphy and low in ectomorphy and arguing that mesomorphy’s associated temperaments (active and aggressive but lacking sensitivity and inhibition) tended to cause delinquency and criminal behaviour. Although his research was groundbreaking, it was criticized on the grounds that his samples were not representative and that he mistook correlation for causation.