It was the work of B. F. Skinner that placed behaviorism into modern psychology. Skinner identified two types of behaviors, respondent behaviors and operant behaviors. Respondent behaviors are controlled by what comes before them, such as the knee-jerk reflex. These were the kinds of behaviors Pavlov and Watson studied. Skinner discovered that the stimuli, or events in the environment, that follow a behavior can cause that behavior to either increase or decrease in strength.
Operant behaviors are a function of their consequences.
They refer to behavior that operates upon the environment to produce effects, outcomes, or consequences. We can judge the effectiveness of an environmental force by the effects it has upon a behavior. A contingency of reinforcement defines the probability that a reinforcing event will follow operant behavior. For example, when a person turns the ignition key of the car, operant. This behavior usually has resulted in the car starting, reinforcement.