Burrhus Frederic Skinner (1904-1990) was the most influential behaviorist psychologist and one of the most cited scientists of the 20th century. He developed the experimental analysis of behavior, demonstrating how behavior is shaped, maintained, and changed by its consequences. His operant conditioning chamber (the "Skinner box") became the standard apparatus for studying learning, and his principles of reinforcement have been applied to education, therapy, organizational management, and animal training.
Operant Conditioning
Skinner distinguished between respondent behavior (elicited by stimuli, as in Pavlovian conditioning) and operant behavior (emitted by the organism and selected by its consequences). Reinforcement increases the probability of behavior: positive reinforcement adds a desirable consequence; negative reinforcement removes an aversive one. Punishment decreases behavior. Skinner mapped the effects of different reinforcement schedules (fixed ratio, variable ratio, fixed interval, variable interval), showing that each produces characteristic patterns of responding — with variable ratio schedules producing the highest, most consistent rates (explaining the persistence of gambling behavior).
Skinner was controversial for his radical behaviorism — the philosophical position that private events (thoughts, feelings) are behaviors subject to the same laws as public behavior, and that mental explanations are unnecessary and misleading. His utopian novel Walden Two envisioned a society engineered through behavioral principles. While cognitive psychology largely replaced behaviorism's theoretical framework, Skinner's empirical principles remain foundational: reinforcement schedules, shaping, stimulus control, and applied behavior analysis (ABA) are used in education, clinical treatment (especially autism intervention), organizational behavior management, and animal training.