History and development of the idea
Carl Jung distinguished between two types of unconscious mind: the personal unconscious and collective unconscious. The personal unconscious was the accumulation of experiences from a person's lifetime that could not be consciously recalled. The collective unconscious, on the other hand, was a sort of universal inheritance of human beings, a "species memory" passed on to each of us, not unlike the motor programs and instincts of other animals. Jung believed the personal unconscious was dominated by complexes.
The term "complex" (German: Komplex; also "emotionally charged complexes" or "feeling-toned complex of ideas"), was adopted by Carl Jung when he was still a close associate of Sigmund Freud. Complexes were so central to Jung's ideas that he originally called his body of theories "Complex psychology". Historically the term originated with Theodor Ziehen, a German psychiatrist who experimented with reaction time in word association test responses. Jung described a "complex" as a 'node' in the unconscious; it may be imagined as a knot of unconscious feelings and beliefs, detectable indirectly, through behavior that is puzzling or hard to account for.
Jung found evidence for complexes very early in his career in the word association tests conducted at the Burghölzli, the psychiatric clinic of Zurich University, where Jung worked from 1900–1908. Jung developed the theory out of his work on Word Association Test. In the word association tests, a researcher reads a list of 100 words to each subject, who was asked to say, as quickly as possible, the first thing that came to mind in response to each word, and the subject's reaction time was measured in fifths of a second. (Sir Francis Galton invented the method in 1879.) Researchers noted any unusual reactions—hesitations, slips of the tongue, signs of emotion. Jung was interested in patterns he detected in subjects' responses, hinting at unconscious feelings and beliefs.
In Jung's theory, complexes may be conscious, partly conscious, or unconscious. Complexes can be positive or negative, resulting in good or bad consequences. There are many kinds of complex, but at the core of any complex is a universal pattern of experience, or archetype. Two of the major complexes Jung wrote about were the anima (a node of unconscious beliefs and feelings in a man's psyche relating to the opposite gender) and animus (the corresponding complex in a woman's psyche). Other major complexes include the mother, father, hero, and more recently, the brother and sister. Jung believed it was perfectly normal to have complexes because everyone has emotional experiences that affect the psyche. Although they are normal, negative complexes can cause us pain and suffering.
One of the key differences between Jungian and Freudian theory is that Jung's thought posits several different kinds of complex. Freud only focused on the Oedipus complex which reflected developmental challenges that face every young boy. He did not take other complexes into account except for the Electra complex, which he briefly spoke of (Carlini, 2005).
After years of working together, Jung broke from Freud, due to disagreements in their ideas, and they each developed their own theories. Jung wanted to distinguish between his and Freud's findings, so he named his theory "analytical psychology".