The Impulse Reduction Theory: What It Is and What It Explains


Impulse reduction theory is a model that became popular in the middle of the last century and it was conceptualized by Clark Hull to explain how behavior, learning and motivation were related.

According to this theory, what favors us to repeat a behavior, that is to learn, is how effective it is in reducing an internal need such as thirst or hunger. The rationale for this theory is that drive reduction is the main force behind motivation.

Although this theory is somewhat out of date today, it does have the merit of having conceptualized behavior in very concrete and mathematical terms, which served as a model for other later theories. Let’s take a closer look at it.

What is impulse reduction theory?

Impulse reduction theory is a theory of motivation originally posed by Clark Hull in 1943 and later developed by his collaborator Kenneth Spence. This model argues that the reduction of impulses is the main force behind the motivation, learning and behavior of an organism and would become the main motivational model of the 40s and 50s.

An impulse or “drive” is defined in this theory as the motivation that arises due to a psychological or physiological need that must be satisfied to recover an optimal state for the organism. It works as an internal stimulus that motivates the individual to activate to satisfy the need that has caused that impulse, reducing it. We would have primary drives that are innate, such as thirst, hunger, and sex, and secondary drives, which are learned through conditioning.

Hull was one of the first theorists to try to create a grand theory that would serve to explain all behavior. He began developing his theory shortly after starting work at Yale University, drawing inspiration from a large number of great thinkers in the behavioral and biological sciences such as Charles Darwin, Ivan Pavlov, John B. Watson, and Edward L. Thorndike.

The theory of impulse reduction was developed as a hypothetical-deductive system in psychology, which consisted of the postulation of participating variables, that is, very precisely defined terms that could be used using mathematical symbols to represent them. So Hull tried to develop a system as scientific as the present in any natural or formal science, an idea taken after reading Isaac Newton and the Greek mathematician Euclid.

Hull was also influenced by the works of Ivan Pavlov, especially taking the principles of conditioning, and from Thorndike he took the idea of ​​the law of effect. In fact, it is from these two great theoretical contributions to the behavioral sciences that Hull tries to integrate a new system by creating his theory of impulse reduction.

 Impulse reduction theory : Homeostasis and learning

Impulse reduction theory : Clark Hull based his theory on the concept of homeostasis, that is, the idea that an organism actively works to maintain internal balance. For example, our body regulates its temperature constantly to avoid being neither too cold nor too hot and thus being able to carry out its organic functions properly. Hull thought that behavior was one of the many ways the body had to maintain its balance, only in a more visible way.

Based on this idea, Hull suggested that motivation, that is, moving to do something, is the result of biological needs. In his theory, Hull used the term “drive” or “impulse” to refer to the state of tension or activation caused by physiological and biological needs. These needs, such as thirst, hunger or seeking warmth, drive us to do something. As we are in an unpleasant state, being in tension, our organism is motivated to solve a need or reduce it.

With the intention of returning to a pleasant state, humans and, also, animals, look for all kinds of ways to satisfy these biological needs. For example, if we are thirsty we look for something to drink, if we are hungry we look for food and if we are cold we put on more clothes. According to Hull, If the behavior performed works to reduce that impulse, that behavior will be repeated in the future in case of the same need.

Conditioning and reinforcement

Although Clark Hull is considered a scientist belonging to the neo-behaviorist current, he agrees with the majority of behaviorists when it comes to considering that human behavior can be explained in terms of conditioning and reinforcement. Based on what he himself states with his theory, the reduction of impulses acts as a reinforcer of a certain behavior.

The establishment of a new behavior that reduces impulses respects the classic stimulus-response relationship, that is, when a stimulus and a response are followed by the reduction of the need, this increases the probability that the same stimulus, if it appears in the future, will generate the same response.

This reinforcement increases the probability that the same behavior will occur again in the future if the same need arises. This makes sense since, for an organism to survive in nature, it must perform behaviors that effectively solve the needs that may arise, learn them and do them again in case the need arises again, since not doing so will run the risk of not regaining homeostasis and therefore putting yourself in danger.

We can understand that an organism is in danger as much as it is facing a serious and potential danger (eg, starvation) as simply feeling a need that causes displeasure the longer it goes unresolved (eg, moderate thirst). Entering a state of need means that the requirements for survival are not being met. In order to satisfy them, the body behaves in a way that focuses on reducing this need.

Deductive mathematical theory of behavior

As we mentioned, Clark Hull proposed a hypothetico-deductive system to be able to explain behavior, with the intention of developing a system as scientific as that of other sciences such as mathematics and physics. His goal was to develop a theory of learning that could be expressed in mathematical terms, and for this he presented a formula:

sEr = V x D x K x J x sHr – sIr – Ir – sOr – sLr


  • sEr: excitatory potential, or the probability that the organism makes a response (r) to a stimulus (s)
  • V: Dynamism of the intensity of the stimulus, meaning that if some stimuli exert great influence on others.
  • D: Impulse force, determined by the degree of biological deprivation.
  • K: Incentive motivation, or the size or magnitude of the goal.
  • J: The delay before the body is able to look for reinforcers.
  • sHr: Force of habit, established by the degree of influence of the previous conditioning.
  • slr: Conditioned inhibition caused by previous lack of reinforcement.
  • lr: Reactive inhibition or fatigue.
  • sOr: Random error.
  • sLr: Threshold of reaction or the smallest amount of reinforcement that will produce a learning.

In Hull’s paradigm there are three indispensable elements in any other behaviorist theory. E, this is stimulus, O which is organism and R which is response, being the paradigm E – O – R. Or is affected by E and determines R. When trying to explain the functioning of the organism, to which we do not have internal access Since it can only be represented as a black box model, if we know what stimuli have entered (input) and what responses the organism has emitted (output), taking into account the previous formula, the behavior and learning of O can be explained.

Criticisms of the theory

Impulse reduction theory was very popular in the middle of the 20th century, however today it is a bit forgotten and the reasons behind it are numerous. Among these we find the exaggerated emphasis on quantifying all behavioral variables, despite not being possible to know everything that influences human behavior, and the theory lacked generalizability. Likewise, it can be said that Hull’s interest in using experimental techniques to address human behavior has had a great impact and influence on later motivational theories.

However, the main problem with this theory is that cannot explain the importance of secondary reinforcers in reducing impulses. Unlike the primary “drives”, such as thirst or hunger, the secondary ones do not intervene directly in the satisfaction of biological needs. An example of this is money, an element that does not quench hunger or thirst directly but that does allow us to obtain reinforcing food and drink that does reduce impulses directly. The need for money acts as a powerful source of basic needs reinforcers.

Another criticism of the model is that the impulse reduction theory does not explain how people, despite being satiated and finding homeostasis, sometimes do not reduce their behavioral urges. For example, on many occasions, after having eaten and having satisfied hunger, we continue to eat more and more, which would be an unnecessary behavior since the function of eating is to reduce the need for hunger.

Finally there is the fact that many people seek tension voluntarily, that is, breaking their homeostasis. Parachute jumping, bungee jumping or diving to great depths are behaviors that lead us to be in tension, just the opposite of homeostasis and make our need to be protected and calm is very unsatisfied. The theory cannot explain why people commit this type of behavior so contrary to what is instinctive.

Although all this has contributed to the fact that Clark Hull’s Impulse reduction theory is not very current today, it is true that it has helped to promote research in psychology from a more scientific perspective, in addition to being the seed for the elaboration of other theories about human behavior that came later. For example, many theories of motivation that emerged during the 1950s and 1960s are based on Hull’s theory or had some influence received from it, such as Maslow’s pyramid, which emerged as an alternative to Hull’s theory. Hull model.


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  1. November 25, 2020

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