Applied behavior analysis
Psychologist John B. Watson founded Behaviorism in 1913 and he is regarded as one of the first psychologists to study the applied science of behavior. He thought that internal feelings should not be studied at all. He also thought that behavior is shaped by the environment over time due to the outcome of a person's actions. He believed all behavior is learned and can be changed. If a person gets something good as a result of doing a behavior they are more likely to repeat that behavior. If something bad happens as a result of a behavior a person is less likely to do that thing again. This is an idea that is used a lot in ABA.