Behaviorism is a systematic approach to understanding the behavior of humans and other animals. It assumes that behavior is either a reflex elicited by the pairing of certain antecedent stimuli in the environment, or a consequence of that individual's history, including especially reinforcement and punishment contingencies, together with the individual's current motivational state and controlling stimuli. Although behaviorists generally accept the important role of heredity in determining behavior, deriving from Skinner's two levels of selection (phylogeny and ontogeny), they focus primarily on environmental events. The cognitive revolution of the late 20th century largely replaced behaviorism as an explanatory theory with cognitive psychology, which unlike behaviorism views internal mental states as explanations for observable behavior.
Behaviorism emerged in the early 1900s as a reaction to depth psychology and other traditional forms of psychology, which often had difficulty making predictions that could be tested experimentally. It was derived from earlier research in the late nineteenth century, such as when Edward Thorndike pioneered the law of effect, a procedure that involved the use of consequences to strengthen or weaken behavior.
