Premack's principle, or the relativity theory of reinforcement,[1] states that more probable behaviors will reinforce less probable behaviors.[2] The principle was derived from a study of Cebus monkeys by Professor David Premack, but has explanatory and predictive power when applied to humans. This is evidenced by the fact that therapists use the principle in behavior modification. Premack's Principle suggests that if a person wants to perform a given activity, the person will perform a less desirable activity to get at the more desirable activity. In behaviorist terms, activities become reinforcers. Students will be more motivated to perform a particular activity if they know that they will be able to partake of a more desirable activity as a consequence. If high-probability behaviors (more desirable behaviors) are made contingent upon lower-probability behaviors (less desirable behaviors), then the lower-probability behaviors are more likely to occur. More desirable behaviors are those students spend more time doing if permitted; less desirable behaviors are those students spend less time doing when free to act.
This psychological principle can be used effectively in certain controllable situations to dramatically affect the behaviors of students.
In behavioral terms Premack's principle states that any high-frequency activity can be used as a reinforcer for any lower-frequency activity. This common statement made by most mothers easily show us how Premack's principle is used "You have to finish your vegetables (low frequency) before you can eat any ice cream (high frequency)" (Wenning, C., no page).
The term behavior change has replaced the term behavior modification because in operant conditioning, one does not modify behavior but instead one modifies the environment (antecedents and consequences) that then results in behavior change.
David Premack and his colleagues conducted many experiments to test the theory of the Premack principle, specifically its effectiveness on humans. One of the earliest studies was conducted with young children. Premack gave the children two response alternatives, which were either eating candy or playing a pinball machine. These responses were measured based on which response was more probable for each individual child. Some of the children preferred one activity over the other. In the second phase of the experiment, the children were tested with one of two procedures. In one procedure, eating was the reinforcing response, and playing pinball served as the instrumental response. This means that children had to play pinball in order to eat candy. The results were consistent with the Premack principle, only the children who preferred eating candy over playing pinball showed a reinforcement effect. In another test, the roles of responses were reversed, and the results were identical to the first procedure. Only children who preferred playing pinball over eating candy showed a reinforcement effect. This study shows that the power of the Premack principle is that any high-probability activity can be an effective reinforcer for a response that the subject is less likely to perform, only if the subject prefers the high-probability activity (Domjan, 2010).