Behaviorism

Behaviorism arose in the late 19th and early 20th century as a reaction to the earlier schools of psychology, such as structuralism, functionalism, and psychoanalysis. It's chief quarrel with these schools was in the lack of observability of which the mind offered. There is, and was in fact, no way to directly observe the mind, and as such, the behavioral school of psychology did something radical and completely counterintuitive to psychology; they did away with the mind completely. The premise being something that is unobservable is as good as not existing. Rather than focusing on the mind, behaviorists found that behavior, as the name behaviorism suggests, or more specifically, directly observable phenomena, should be the focus of psychology.

Behaviorism, being heavily influenced by Darwinian theory, was very concerned with learning. As learning is the method by which conscious organisms are able to quickly adapt to challenging environments. Similar to structuralism, behaviorism can be seen as the embodiment of the 8 roots of psychology, and by many accounts behaviorism is this more so. In particular, behaviorism took heavy influence from the concept of critical empiricism, in their insistence on the direct observability of phenomena, and scientific materialism, in their stating that for all practical purposes the mind does not exist or at least is simply a byproduct of the physical body.

John Watson is considered the champion of behavioral psychology, his theory and research inspired countless others along similar paths, including the later BF Skinner who continued and expanded upon the groundwork which Watson put forth.