Behaviorism describes positions ranging from the belief that the study of behavior is independently valuable of other concerns, to the claim that behavior is the one appropriate subject of psychology, and sometimes that mental terms (belief, goal, etc.) have no referents and/or only refer to behavior.
Early in the 20th century, John B. Watson argued for the value of a psychology which concerned itself with behavior in and of itself, not as a method of studying consciousness. This was a substantial break from the structuralist psychology of the time, which used the method of introspection and considered the study of behavior valueless. Watson, in contrast, studied the adjustment of organisms to their environments, more specifically the particular stimuli leading organisms to make their responses. Much of Watson's work was comparative, i.e., he manipulated and observed changes in the behavior of animals. Watson's work was much influenced by the work of Russian physiologist I.P. Pavlov, who stumbled upon the phenomenon of classical conditioning (which were essentially learned reflexes) in his study of the digestive system of the dog, in that it heavily emphasized physiology and the role of stimuli in producing conditioned responses. For this reason, Watson has often been described as an S-R (stimulus-response) psychologist.
B.F. Skinner, who was more active in the 40s and 50s, developed a distinct kind of behaviorist philosophy, often called radical behaviorism[?], and science, called behavior analysis[?] or the experimental analysis of behavior[?]. Of particular importance was his concept of the operant response. In contrast with the idea of a physiological response, an operant is a class of structurally distinct but functionally equivalent responses. For example, while a rat might press a lever with its left paw or its right paw or its tail, all of these responses share a common function, a common consequence. Operants are often thought of as species of responses, where the individuals differ but the class coheres in its function--shared consequences with operants and reproductive success with species.
This is one of many clear distinctions between Skinner's notions and the S-R notions of many of his predecessors. Another crucial concept, that of reinforcement, was defined in terms of prior observation - if an event was experimentally observed to increase the rate of response, it was then called a reinforcer for that particular animal at that time. Food, water, brain stimulation, sex, social contact, and reinforcing drugs are all reinforcers that have been used in operant research with animals.
The idea of reinforcement expanded on earlier work on trial-and-error learning by researchers such as Thorndike and Guthrie with both conceptual reformulations - the notion of a stimulus-response 'association' was abandoned - and methodological ones - the institution of 'free operant' procedures, so called because the animal was now permitted to respond at its own rate. With this method, Skinner carried out substantial experimental work on the effects of different schedules and rates of reinforcement on the rates of operant responses made by rats and pigeons.
In fact, there were many behaviorists other than Watson and Skinner. Among the important forerunners of behaviorism were Pavlov (the discoverer of classical conditioning) and Thorndike (who studied cats' abilities to escape from puzzle boxes). Hull was another famous behaviorist, representative of the variant called neo-behaviorism. Tolman developed much of what would later become the cognitivist program, arguing that rats constructed cognitive maps of the mazes they learned even in the absence of reward, and that the connection between stimulus and response (S->R) was mediated by a third term - the organism (S->O->R). His approach has been called, among other things, purposive behaviorism.
Since the beginning of the 20th century, many other behaviorists have worked in this field and have taken a variety of different views. Even now, behaviorists are still prone to hold a wide variety of views: to favor one or another approach, to study all different species, to integrate their work with psychobiological work, and to take up some of the topics also studied in cognitive science, such as concept formation. In fact, notwithstanding the heavy balkanization of cognitive scientists against behaviorism (understood generically to refer to some mixture of Skinner's philosophical views and Watson's views on psychology and methods) it could indeed be said that the study of behavior is part of cognitive science, or conversely that cognition is part of the study of behavior (a common claim of Skinner's). Modern cognitive science is also dominated by a early 20th century behaviorism (in the sense that introspection is not admissible data) and owes a great deal to behaviorism, even in formulating its arguments against behaviorism. Indeed, one of the most well-known behaviorists, Hull[?], could well be described as the first cognitive psychologist.
Methodological behaviorism[?] considers thoughts and feelings as special cases of human behavior that cannot be studied directly, but must be inferred from verbal reports, physiological studies, etc. Most modern psychologists are methodological behaviorists.
Leading developers of behaviorism (in rough chronological order):
See also: conditioning