Although psychology describes one branch of science that deals with mental processes and behavior, it has many different theories. Some of these theories have been more accepted than others at particular times in history, but all have played a role in shaping the discipline of psychology.
In the 1950s behaviorism became the dominant school of thought in the United States. Behaviorism was developed around the idea that an organisms response was caused by stimuli in the environment. The idea of “classical condition” initially developed in the functionalist school became a bedrock of behaviorist theory. Psychologist B.F. Skinner became the most famous leader of this movement and conducted many experiments that led to an increased understanding of why people behave the way they do. Skinner’s emphasis was on observing behavior because he believed the inner workings of the mind were unavailable to observation. He preferred to run experiments that resulted in clearly observable behavior that could be recorded and modified by changing stimuli.
Cognitive psychology focuses on mental processes such as how people think, perceive, remember and learn. It is tightly related to the disciplines of neuroscience, philosophy and linguistics. Cognitive theories strive to explain how people store and process new information. Until the 1970's behaviorism was the dominant school of thought in psychology. However, at that point cognitivism began to take over. Cognitive theories are primarily focused on internal mental states -- something that could not be studied by the cut and dry nature of behaviorism.
Structuralism was the first school of psychology and the founder of the first psychology lab, Wilhelm Wundt, is credited with establishing the principles (although the name "structuralism" is credited to his student, Edward B. Titchener). Essentially, structuralist theories strived to break down mental processes into the most basic components. While the many criticisms of structural methodology eventually relegated this school of thought to obscurity, it is credited with laying the experimental basis for modern psychology.
Humanism rose to popularity in the 1950s as a response to psychotherapy and behaviorist theories. While many schools of psychology up to this point placed a lot of emphasis on understanding behavior and thought, humanist theories were the first to place emphasis on each individual’s potential. Humanists were interested in studying the importance of growth and the self-actualization of real people. One of the most important individuals in this movement, Abraham Maslow, developed a framework that strived to articulate how people could reach the point of self-actualization. What became known as Maslow’s Hierarchy of Needs showed how people had to reach certain levels of prerequisites before the mental and physical resources could be focused on the higher goal of actualization. Humanist theories were criticized as being too subjective but succeeded in re-injecting some humanity back into the field of psychology.
Arguably the most famous psychologist, Sigmund Freud developed a new theory of psychology known as psychoanalysis. Freud’s focus was on the unconscious mind and how it influences behavior. Most notably, his psychosexual stages and dream symbolism remain some of the most talked about topics in psychology today. Although much of his work is viewed with skepticism today, the taboo nature of his research led to vast interest among laypeople. As with most psychological theories, while large portions of it are no longer accepted, large aspects of it are still important today. Erik Erikson’s theory of psychosocial stages and even Freud’s psychosexual stage theory remain important contributors to our understanding of personality and personality development.
Other important theories of psychology include gestalt, existentialism, comparative, clinical and developmental. Because psychology deals with such a broad topic as the human mind and behavior, various theories have arisen to help explain different factors and pieces.