FUNCTIONALISM

Functionalism has held for several years a dominant position among the contemporary sociological theories. In functionalism society it is conceived as a set of interconnected parts between them. None of them, therefore, can be understood isolated from the other, but only in its context.

The relationships between the parts of the company are functional, and each element performs a particular task which if combined with all the others things, helps to create and keep working that part of the world that we call society. 

There exists, therefore, for functionalism a state of equilibrium in society, that is happen when each part performs its job properly. For this reason we can say that the functionalism is based on the model of the organic system that we find in the life sciences.

Functionalism is a line of research in psychology, which begin in the United States in the late nineteenth century by William James and John Dewey, who plays psychic phenomena not as separate elements from each other (as he tried to do the contemporary European structuralism Edward Titchener) but as functions by which the body adapts to the social and physical.

The manifesto of functionalism is considered the classic article "The Province of Functional Psychology", James Rowland Angell (1907). In the article, Angell argues that mental functions are not "abstract entities", but are the result of evolutionary processes functional in humans mediate the relationship between the environment and needs of the organism.

Although functionalism, as school specific psychological, has seen a decline since the late '20s (in conjunction with the growth of the contemporary academic psychology, behavior modification in the US), some of its basic assumptions are filtered within the principles implicit in contemporary psychological research, both in specific sectors such as Evolutionary Psychology that, in general, most of the Cognitive Science.

References:

https://en.wikipedia.org/wiki/Structural_functionalism

http://study.com/academy/lesson/structural-functional-theory-in-sociology-definition-examples-quiz.html