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Hull's Theory

Biological motives are built into the org­anism. They include hunger, thirst, pursuit of pleasure, and avoidance of pain.

Hull's theory was one of the first system­atic attempts to explain motivation. Hull thought he would explain all behavior of all organisms: a very ambitious goal.

Few theories in the history of psychology started with such high aspirations and failed so completely. Hull's theory once dominated American psychology; now it has all but disappeared.

How was Hull's theory ambitious?

Hullian research led to the old stereotype of experimental psychologists as lab-coated figures watching rats run through mazes. Hull and other researchers performed many thousands of experiments with rats in mazes, trying to discover basic laws of motivation.

For beginning students, Hull's theory remains relevant in several ways. First, the story of its rise and fall is a case study in scientific research. Second, Hull's emphasis on homeostasis is echoed in more modern studies of biological motives as regulatory systems.

Why should students know about Hull's theory?

Understanding Hull's theory helps one understand motivational theories that came later. Most were reactions to perceived deficiencies in Hull's theory.

In this respect, Hull's theory is like Freud's: one must know about it in order to make sense of what came after it. It was a very influential theory.

The Hullian Approach

In the 1930s, Clark Hull undertook to construct a grand theory that he thought would unite all psychology. He based his theory on the concept of homeostasis, borrowed from biology.

Homeostasis is a word that refers to the active regulation of critical biological variables. For example, your kidney regulates the salt and water balance in your body, and your pancreas regulates blood sugar.

To Hull, behavior was another way the organism regulated itself or kept itself alive and healthy. To him it made sense that a theory of motivation would borrow from scientific knowledge about homeostatic processes.

portrait of Clark Hull
Clark Hull

Scientists knew about biological regulation as early as the mid-1800s. The concept of homeostasis was not widely discussed until Walter B. Cannon's 1932 book The Wisdom of the Body.

Cannon pointed out that organisms work to keep biological variables within a healthy or normal range. There are many homeostatic systems in the body. Levels of blood pressure, salt, glucose, water, and carbon dioxide (among other things) must be maintained within normal ranges, for the health of the organism.

What concept was featured in Cannon's book?

Hull reasoned that homeostatic mechan­isms might provide a scientific explan­ation of motivation. Behavior could be regarded as an outward expression of the organism's pursuit of biological health.

For example, you shiver to get warm. That is a homeostatic mechanism built into the body. If that fails, you are motiv­ated to carry out a behavior such as putting on a sweater or finding a heater.

Many behaviors are extensions of homeostatic mechanisms. Think how many human behaviors are related to eating, which is itself aimed at main­taining glucose and fat levels in our bodies.

Where did motivation come from, according to Hull?

Hull conceived of all motivation as coming originally from biological imbalances or needs. The organism was thrown into movement–was motivat­ed–when it needed something that was not present at its current location.

A need, in Hull's system, was a biolog­ical requirement of the organism. Hunger was the need for more energy. Thirst was the need for more water. Motivation, to Hull, was aimed at making up or erasing a deficiency or lack of needed in the organism.

Hull used the word drive to describe the state of behavioral arousal resulting from a biological need. In Hull's system, drive was the energy that powered behavior.

Drive was not pleasant. Drive was an uncomfortable state resulting from a biological need, so drive was something the animal tried to eliminate. The animal searched for food in order to reduce the hunger drive.

Why was Hull's theory called a "drive-reduction" theory?

Hull believed that when a need occurred again, the animal would repeat a behavior that reduced the drive on a previous occasion. Hull's theory was called a drive-reduction theory of motivation. Reducing a drive provided reinforcement for behavior.

Hull's theory inspired an enormous amount of research. No other psychological theory was so daringly precise.

Hull used specific formulas to predict the likelihood of specific behaviors. He specified that the probability that a particular stimulus would lead to a particular response (the "excitation potential") using a formula.

Excitation potential =

S H R [D x K x J x V]...where....

S H R was the number of reinforced training trials

D was the amount of biological deprivation or drive

K was the size or magnitude of the goal

J was the delay before the animal was allowed to pursue the goal

V was the intensity of the stimulus that set off the behavior

Each variable was given a precise operational definition, to aid research and replication. Hull hoped to make psychology as scientific and precise in its predictions as physics or chemistry.

However, things did not work out well for Hullian researchers. Predictions based on Hull's equations often did not come true.

Researchers responded by altering the system, adding variables or subtracting others, adjusting parameters, trying to make it all work. Finally researchers began to realize it was never going to work. There could not be such a simple and precise system for predicting animal behavior.

What happened to Hull's theory?

The abandonment of Hull's theory occurred about 30 years after he proposed it. An entire generation of researchers had followed a false lead.

By the early 1970s journal articles contained bitter references to "30 years of fruitless Hullian research." The study of learning veered off into different directions. Bolles (1990) commented, "Hull would have been unable to read a present-day research paper; none of it would have made any sense!"

Hull's theory may have disappeared from present day motivational research, but it had a big impact on the field. Many motivational theories of the 1950s and 1960s were reactions to Hullian theory.

These included the proposals for cognitive motives as well as Maslow's motivational psychology, both discussed later in this chapter. All were invented as alternatives to Hull's drive-reduction approach.


Bolles, R. C. (1990). Where did everybody go? Psychological Science, 1, 107, 112-113.

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