Drive Reduction Theory

In the 1940s and 1950s, behaviorist Clark Hull set out to explain behavior with his drive reduction theory. Essentially, Hull believed that all people have biological needs—which he referred to as “drives”—that motivate our behaviors and create unpleasant states. Hull believed that these drives were internal states of tension or arousal that were physiological or biological in nature. The primary influence of motivation came from the desire to reduce these drives, which Hull believed was critical in order to maintain an internal calm. Common examples of drives in Hull’s conception include thirst, hunger, and the need to be warm. To reduce these drives, we drink liquids, eat food, and put on extra clothing or turn up the heat on our thermostats.

Drawing on the works of Ivan Pavlov, Charles Darwin, and John B. Watson, among others, Hull based the drive reduction theory on the notion of homeostasis, believing that behavior was one method of maintaining balance.

Doctoral Definition

Homeostasis: The idea that the body needs to reach a level of equilibrium, or balance, and then maintain that state. For example, the way the body regulates body temperature.

Hull was considered a neo-behaviorist and believed that behavior could be explained with conditioning and reinforcement. A behavior is reinforced by the reduction of a drive, and this reinforcement will increase the chances of that behavior occurring again, should the need arise in the future.


Along with the theory of drive reduction, Hull attempted to create a formula of learning and behavior that could empirically accompany his theories and offer a deeper and more technical understanding of how drives influence action and thought. His resulting equation, known as the Mathematico-Deductive Theory of Behavior, is:

sEr: This stands for excitatory potential, meaning the chance that an organism will create a response (r) to a stimulus (s)

V: The stimulus

D: The strength of the drive, determined by the amount of biological deprivation

K: The size of the goal, known as the incentive motivation

J: The delay before reinforcement can be sought

sHr: The strength of the habit, as determined by the amount of conditioning that occurred previously

sIr: This is known as the conditioned inhibition, and it is the result of a previous absence or lack of reinforcement

Ir: This is the reaction inhibition, otherwise known as lethargy or fatigue
sOr: An allowance for error that is random

sLr: This is the reaction threshold, or the lowest amount of reinforcement needed to create learning


While Hull’s work on the scientific method and experimental techniques left a profound impact on the world of psychology, his drive reduction theory is largely ignored today. As a result of the narrowly defined variables in his accompanying formula, his theory makes it difficult to create predictions based on recurring experiences.

One of the largest issues with Hull’s drive reduction theory is that it does not take into account the role of secondary reinforcers and how they play a part in reducing drive. Where primary reinforcers deal with drives that are biological or physiological in nature, secondary reinforcers do not reduce these biological or physiological needs in a direct manner. Money, for example, is a secondary reinforcer. Money cannot reduce a drive; however it is a source of reinforcement, and can allow one to obtain a primary reinforcer to reduce a drive.

Another criticism of Hull’s drive reduction theory is that there is no explanation as to why a person will engage in certain behaviors that do not actually reduce drives. Why would a person drink if they are not thirsty? Why would they eat if they are not hungry? Some people will even increase tension by participating in activities like bungee jumping and skydiving. These activities do not fulfill any sort of biological need and even place the participant in danger. Ultimately, though it is a flawed theory, Hull’s work on drive reduction spurred a generation of psychologists to attempt a deeper understanding of the precise factors that cause humans to act and react in their environments.