Clark L. Hull

Clark Leonard Hull was an American psychologist who aimed to explain learning and motivation using scientific, law-like principles of behavior. He is well known for his intellectual clashes with Edward C. Tolman and for developing drive theory. Hull spent the bulk of his career at Yale University, having been brought there by James Rowland Angell, the university’s president and a former psychologist. Through his research, Hull showed that his theories could actually predict behavior. His major publications include *Mathematico-Deductive Theory of Rote Learning* (1940) and *Principles of Behavior* (1943), the latter of which made his analysis of animal learning and conditioning the leading theory of its era. Hull’s model is framed in biological terms: an organism experiences deprivation, which creates needs; those needs activate drives; drives then trigger behavior; that behavior is goal-directed; and reaching the goal has survival value.

He is perhaps most famous for the “goal gradient” effect, the idea that organisms put in a disproportionate amount of effort during the final stages of reaching a drive’s object. Because behaviorism has fallen out of favor in modern psychology, Hull’s work is now rarely cited or is considered outdated—though more recent cognitive research has found renewed support for goal-gradient-like effects in demanding mental tasks. Even so, a 2002 survey from the *Review of General Psychology* ranked Hull as the 21st most cited psychologist of the 20th century.

Hull was born in a log house in Akron, New York, on May 24, 1884. His father, a largely uneducated man with a violent temper, had worked heavily as a child and never learned to read; his mother, a shy woman from Connecticut, eventually taught him. When Hull was three or four, his family moved to a farm in Michigan, where he and his younger brother, Wayne, helped with manual labor and household chores. He attended a small, one-room school in the village of Sickels, with about twenty to thirty students, and often missed class to work on the farm. He showed an early talent for mathematics but struggled with grammar. Around age 11 or 12, he was forcibly converted by a group called the Christian Crusaders, an experience that led him to rethink his religious identity and eventually reject religion entirely. At 17, he passed a teacher’s examination and began teaching in a similar small schoolhouse. His religious crisis and teaching experience pushed him to seek more education. He attended a high school in west Saginaw County, living with the superintendent of schools in exchange for chores. Hull’s atheism nearly got him thrown out, but the superintendent’s wife convinced her husband to let him stay. After finishing high school, he left the superintendent’s home but kept in touch until the man’s death.

After high school, Hull studied at Alma Academy, where he continued to excel in mathematics, especially geometry. His interest in geometry sparked thoughts about how the mind forms new connections based on existing knowledge. While at the academy, he read the works of Baruch Spinoza, whom he admired but ultimately disagreed with. Just before graduating, he attended a banquet where the food was contaminated, contracting a near-fatal case of typhoid that delayed his return to college. Many died during that outbreak, and Hull himself nearly did; he was left with permanent amnesia and a poor memory for names that lasted his whole life. As he recovered, he returned to Alma College, studying math, physics, and chemistry with the goal of becoming an engineer. He planned to qualify for a mining engineering program elsewhere.

After two years at Alma College, Hull moved to Hibbing, Minnesota, to work as an apprentice mining engineer. But two months later, he contracted polio, which paralyzed one leg. He spent a year recovering at his parents’ home and had to reconsider his career path. He thought about becoming a Unitarian minister, drawn to their philosophy-focused sermons. His love of philosophy eventually led him to psychology, which he studied during his recovery. He started by reading William James’ *The Principles of Psychology* and took a special interest in the work of Watson and Pavlov. Early on, his eyes grew weak, so his mother read to him until his eyesight improved. A year later, he returned to teaching in the same one-room school, which had expanded to two rooms. After two more years of teaching, he married Bertha Iutzi with very little money.

He and Bertha then both attended the University of Michigan, where he formally began studying psychology and earned his bachelor’s degree in 1913. After teaching in Kentucky, he took a teaching assistant position at the University of Wisconsin under Joseph Jastrow to enter their graduate program. While taking classes and working, he privately researched the evolution of concepts, which later became his dissertation, “Quantitative Aspects of the Evolution of Concepts.” After graduating, he worked as a half-time assistant and then as a full-time instructor at the University of Wisconsin before moving to Yale.

In 1929, Hull began working at Yale University, where he served as a Sterling Professor until his death.