Freud's theory proposed that the mind can be divided into three main parts. These are the id, ego and superego. The id contains innate sexual and aggressive instincts and works alongside the pleasure principle, which searches for immediate satisfaction. The ego is the conscious, rational mind and works on the reality principle. Last is the superego. This is the conscience and knows between right and wrong. These can be related to personality s each person may be dominated by a part of the mind. For example, people who are dominated by their Id are said to be 'erotic' and seek pleasure.
Freud also defined stages of psychosexual development. These stages are oral, anal, phallic, latency and genital. If a child experiences severe problems or excessive pleasure at any stage during development, this can lead to fixation which can then lead to differences in personality. Regression can also occur if adults experience stressful situations. Freud believed that both fixation and regression play important roles in determining adult personality.
A good example of this can be seen in children that become fixated on the anal stage. They feel that they can control their bodily functions and enjoy retaining faeces. Fixation on retaining faeces can lead to an anal retentive personality type. This type is characterised as being clean, orderly and obstinate.
Ego defence is also a process involved in the development of personality. There are a variety of defence mechanisms used as protection by the ego. Denial is a very good example of this. This is refusing to accept the existence of a threatening event e.g. some patients suffering from a life-threatening illness may deny that the illness is affecting their lives. Freud saw these defences as unhealthy and believed that they affecting personality development.
Much of Freud's work was supported by other research evidence whereas others conflicted with his work. Evidence supporting Freud's theory of fixation was published by Rosenwald (1972). He found that people who scored high for anal retentiveness were reluctant to put their hands into a brown substance resembling excrement. This suggests that anal retentives do have anxieties about faeces.
Freud's theory can also be used to explain 'inconsistency' ('part of me wants to, but the other part doesn't'). it also largely omitted social influences and promoted a deterministic, biological view.
Also criticisms of Freud's theory include that Freud conducted his study on middle-classes white Viennese women and so is hard to generalise for other cultures.