Behaviorism

The school of psychology founded by John Broadus Watson in the early 1900s. Watson tried to make psychology more scientific by excluding those things from its study that couldn't be empirically observed. He felt that the subject matter of psychology should be restricted to observable behavior, rather than consciousness as the structuralists contended. Because consciousness cannot be observed by others, Watson argued that it did not meet the empirical test for science (see Empiricism). In laying out his plans for this new natural science of psychology, Watson emphasized the role of the environment because the environment could be observed and objectively measured.
So confident was Watson of the influence of environment that he issued the following challenge:

"Give me a dozen healthy infants, well-formed and my own specific world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select — a doctor, lawyer, artist, merchant-chief and, yes, even into a beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations and race of his ancestors" [JB Watson, “What the nursery has to say about instincts,” in Carl Murchison, ed., Psychologies of 1925 (Worcester, MA: Clark University Press, 1926), p. 10]

Watson was resolute in insisting that psychology conform to the empirical requirements of science. He stormed into psychology like Attila the Hun and threw out all the non-observables.
What about the mind? No such thing, Watson and his followers declared. If you can't see it, hear it, taste it or smell it — it doesn't exist. (This was termed "radical behaviorism" and is still espoused by some psychologists.) For Watson, the only way to study psychological phenomena was by objective observation — the method of all legitimate sciences.

Perhaps Watson's best known experiment was "Little Albert" in which he and his graduate assistant paramour, Rosalie Raynor (who he later married), ostensibly showed that a neurotic fear in a small child could be produced through simple conditioning — repeatedly pairing a loud noise with a white rat. This challenged the prevailing psychoanalytic viewpoint that such neuroses were the result of unresolved unconscious conflicts. Of course, Watson's big complaint about psychoanalysis was that the unconscious, by definition, is unobservable.

With its scientific appeal, Behaviorism dominated experimental psychology well into the 1940s and probably achieved its greatest influence through the writings of B. F. Skinner.