This method was first popularized by Watson, and then continued mainly by B. F. Skinner, and he believed that studying anything other then observable behavior made psychology less of a science.

The psychodynamic approach continues to focus on the inner forces, conflicts, or instincts of the unconscious that may affect behavior. Carl Jung, a friend of Freud, suggested that the unconscious is influenced by beliefs that we inherit-ideas that are part of every civilization. He called these beliefs the "collective unconsicious." Karen Horney proposed that social forces, such as the need for love, influence the unconscious. Alfred Adler emphasized the unconscious need of the individual to feel worthwhile and important. "The World of Psychology"(11-13)

Introduction to Psychology. N.p.: Nextext, n.d. Print.

Psychologist John B. Watson describes behavior as the relationship between stimuli and responses. A stimulus can cause a response or a response can be traced back to a stimulus. According to Watson, "life's most complicated acts are but combinations of these simple stimulus- response patterns of behavior." He studied the behavior of both animals and children and concluded that humans are simply more complicated than animals but operated on the same principles.

More in depth on Freuds thoughts of the unconscious mind and what it holds.

"unconsciouse mind." wikipedia. N.p., n.d. Web. 19 Jan. 2015. 
 <http://en.wikipedia.org/wiki/Unconscious_mind>.