The second phase of behaviorism, neobehaviorism, was associated with Edward C. Tolman (1886–1959), Clark Hull (1884–1952), and B. F. Skinner (1904–1990). Like Thorndike, Watson, and Pavlov, the neobehaviorists believed that the study of learning and a focus on rigorously objective observational methods were the keys to a scientific psychology. Unlike their predecessors, however, the neobehaviorists were more self-consciously trying to formalize the laws of behavior. They were also influenced by the Vienna Circle of logical positivists, a group of philosophers led by Rudolph Carnap (1891–1970), Otto Neurath (1882–1945), and Herbert Feigl (1902–1988), who argued that meaningful statements about the world had to be cast as statements about physical observations. Anything else was metaphysics or nonsense, not science, and had to be rejected. Knowledge, according to the logical positivists, had to be built on an observational base, and could be verified to the extent that it was in keeping with observation.
A professor of psychology at the University of California at Berkeley, Tolman focused his experimental work largely on white rats learning their way through mazes. He differed from his behaviorist predecessors by taking a more holistic approach to behavior than they had. Rather than talking in terms of atomistic, isolated stimuli and responses, Tolman emphasized their integration with the environment by referring to them as "stimulating agencies" and "behavior acts." In his 1932 Purposive Behavior in Animals and Men, Tolman argued that purpose and cognition were essential to behavior and should be interpreted not as mentalistic entities but as outwardly observable features of behavior describable in objective language. He also defined the notion of the intervening variable, a link between stimulus and response that helps to determine behavior. As many as ten intervening variables could exist between a stimulating agency and a rat's decision to move in a certain direction at a choice-point in a maze.
Of the three neobehaviorists, Hull was the most ambitious about constructing a formal theory of behavior. He believed he had found the fundamental law of learning or habit-formation—the law of stimulus generalization—and that this law not only underlay all behavior in animals and humans, but was a principle basic enough to unify all the social sciences. According to the law, a response could be called forth by an unconventional stimulus as long as that stimulus was associated, either temporally or in character, with the stimulus that usually called forth the response. As long as the unconventional stimulus was similar enough to the usual one, it could elicit the response. Pavlov had noted this effect when his dogs salivated at the ringing of a bell. Hull further theorized that learning was continuous—that is, when an animal was trained to respond to a particular positive stimulus (or avoid a negative stimulus), all aspects of that stimulus impinging on the animal's sensorium were gradually associated with that response. Thus the animal learns in an incremental way, not in an all-or-nothing burst, and thus engineering the appearance of stimuli could precisely control the animal's ability to form habits. These laws of behavior explained how all learning took place without resorting to immaterial notions like soul or free will. Hull, who had originally intended to become an engineer, even designed a variety of machines that worked on the principles of conditioning reflexes, in order to demonstrate that learning was a wholly mechanistic process. He expressed his laws of behavior in mathematical terms, filling his 1943 Principles of Behavior: An Introduction to Behavior Theory with complex equations.
The rigor for which Hull strove in his science was evident both in his exclusion of any nonmaterial entity and in his formulation of laws. It was also evident in the hypothetico-deductive method by which he believed psychologists must work. Here Hull's inspiration was the certainty of scientific knowledge achieved by the natural philosopher Isaac Newton (1642–1727). In Hull's method, the theorist began with the observation of a certain behavior, derived axioms from that observation, deduced consequences from the axioms, tested the consequences through experiment, and then refined the axioms, ultimately establishing the laws of behavior on a firm observational and experimental footing. In 1929 Hull moved from his teaching position at the University of Wisconsin at Madison to a prestigious post at the Rockefeller Foundation–funded Institute of Human Relations at Yale, where he remained until his death in 1952. Hull's laws of behavior and his rigorous scientific method became central to the Institute's mission to unify the social sciences. Hull's theory of behavior integrated psychology, psychiatry, sociology, and anthropology by describing learning as the forging of connections between stimulus and response, and then envisioning this mechanism as the mediator of all social and cultural activity. The build-up and breakdown of habit was thus interpreted as the key to all behavior. Hull and his work formed the focal points of the Institute of Human Relations, which lasted only as long as Hull lived and was dissolved after his death. His approach was, however, continued by his friend and supporter Kenneth Spence (1907–1967), a psychologist at the University of Iowa.
The Harvard psychologist B. F. Skinner, the third of the important neobehaviorists, rejected Hull's attempts at formal theory building and returned to the Watsonian project of founding a science entirely on the observation of behavior. Skinner devised an experimental set-up, the so-called Skinner box, in which a pigeon or a rat would be rewarded for accomplishing an act, such as raising its head above a certain line, or pressing a lever, by the release of food pellets. In his 1938 Behavior of Organisms, Skinner explained that a movement rewarded in this way was reinforced—that is, made more likely to occur—while one that was punished was stamped out. A behavior that was followed by the repetition of that behavior—a movement selected and maintained by its positive consequences—Skinner called the operant. His approach therefore was referred to as operant conditioning. Both animals and people behave the way they do because of the positive consequences produced by past behavior. For Skinner, all learning was a matter of such reinforcement, and his method consisted of recording sequences of movements that revealed the patterns by which behavior was reinforced. He avoided talking about habit formation, and even about stimuli, restricting his science to the observation of these movement patterns.
In his 1953 Science and Human Behavior, Skinner explained the principles that underlay his psychology. First, he argued that his science was entirely based in observation, and that theories and hypotheses played a limited role in it: his approach was radically inductivist and empiricist. Second, since psychology was supposed to be restricted to the level of behavioral observation, it had no need of being reduced to or explained in terms of physiology. Physiology was not more fundamental than psychology—it was either unobservable, hence unscientific, or part of behavior itself. Third, for Skinner, mental processes or states were to be interpreted as behavior—memory, knowledge, imagery, and other such mentalistic entities he dismissed as metaphors or fictions. Past consequences of behavior, not mental states, motivated future action. Skinner's 1957 Verbal Behavior was his attempt to deal with thought and language in terms of reinforced movements. Finally, Skinner believed that biological adaptation was the ultimate criterion for the persistence of a behavior: if an action aided survival, it persisted.
Skinner argued that behavior could be shaped, or controlled, by controlling the rewards or reinforcements meted out in response to them—that is, by controlling the environment. In the mid 1950s and 1960s, some penal and psychiatric institutions adopted this method of behavior modification to shape the behavior of their inmates. In his 1948 book Walden Two, Skinner had prepared the ground for such application of his science by imagining a utopian community led according to behaviorist principles. In his 1971 Beyond Freedom and Dignity, Skinner argued that such ethical principles as free will and individual responsibility are simply illusions, and what will make us truly free is the realization that behavior is instead controlled by the past and by the environment.
Neobehaviorism came in for strong criticism in the late 1950s and 1960s. Philosophers of science questioned the claim that any science could be theory-neutral and based solely in observation; observations were themselves seen to be theory-laden. Psychologists questioned the idea that learning was a singular entity that could form the basis for all of psychology. In particular, cognitive psychology, drawing on insights from computer science, redefined mental processes such as problem solving, learning, and memory in terms of information processing, a development that gave a new autonomy and a new respectability to the study of internal mental states. Influenced by this cognitivist turn, the psycholinguist Noam Chomsky (b. 1928) published a scathing review of Skinner's Verbal Behavior, arguing that language had to be understood in terms of universal and innate mental structures, not as behavior shaped by the environment. Behaviorism is currently regarded by psychologists as one approach among many; both cognitivism and neuroscience are arguably as influential in understanding mind and behavior.
Amsel, Abram. Behaviorism, Neobehaviorism, and Cognitivism in Learning Theory: Historical and Contemporary Perspectives. Hillsdale, N.J.: Erlbaum, 1989.
Boakes, Robert. From Darwin to Behaviorism: Psychology and the Minds of Animals. New York: Cambridge University Press, 1984.
Buckley, Kerry. Mechanical Man: John Broadus Watson and the Beginnings of Behaviorism. New York: Guilford Press, 1989.
Harris, Benjamin. "Whatever Happened to Little Albert?" American Psychologist 34 (1979): 151–160.
Hull, Clark L. Principles of Behavior: An Introduction to Behavior Theory. New York: Appleton Century Crofts, 1943.
Mills, John A. Control: A History of Behavioral Psychology. New York: New York University Press, 1998.
Morawski, J. G. "Organizing Knowledge and Behavior at Yale's Institute of Human Relations." Isis 77 (1986): 219–242.
O'Donnell, John M. The Origins of Behaviorism: American Psychology, 1870–1920. New York: New York University Press, 1985.
Pavlov, Ivan P. Conditioned Reflexes. Translated by G. Anrep. Oxford: Oxford University Press, 1927.
Samelson, Franz. "Struggle for Scientific Authority: The Reception of Watson's Behaviorism, 1913–1920." JHBS 17 (1981): 399–425.
Skinner, B. F. The Behavior of Organisms. New York: Appleton Century Crofts, 1938.
Smith, Laurence D. Behaviorism and Logical Positivism: A Reassessment of the Alliance. Stanford, Calif.: Stanford University Press, 1986.
Tolman, Edward C. "A New Formula for Behaviorism." Psychological Review 29 (1922): 44–53.
Watson, John B. "Psychology as the Behaviorist Views It." Psychological Review 20 (1913): 158–178.
Weidman, Nadine M. Constructing Scientific Psychology: Karl Lashley's Mind-Brain Debates. New York: Cambridge University Press, 1999.