Extrapolating from experiments he conducted with pigeons, B.F. Skinner demonstrated how learning occurs as a consequence of behavior. Whereas classical conditioning is learning by association (S > R), operant conditioning influences learning and behavior using rewards and punishments (R < S). Skinner proposed that a person's behavior is instrumental in determining if learning occurs (Skinner, n.d.). In other words, if a person experiences a pleasant outcome because of their behavior, that person is likely to repeat that behavior. Similarly, if a person's actions result in an unpleasant outcome, the person is less likely to repeat the behavior.

Skinner's work on operant conditioning resulted in the philosophy of radical behaviorism, in which efficient causes drive all behavior. In other words, external events cause all behavior. Skinner did not dismiss internal states, like feelings, emotions, and thoughts; however, he argued that "internal states are not the causes of our behavior but one of its results" (Goldhaber, 2000, p. 77). In short, radical behaviorism held that human thinking processes are not important.