Each stage (apart from latency) is marked by a different conflict that the child must resolve in order to progress successfully to the next stage
Any psychosexual conflict that is unresolved leads to fixation where the child becomes 'stuck' and carries certain behaviours and conflicts associated with that stage through to adult life
Freud's theory is controversial in many ways, and occasionally bizarre, but it has nevertheless had a huge influence on psychology and contemporary thought
Many of Freud's concepts (such as the Id and the Oedipus complex) are said to occur at an unconscious level, making them difficult, if not impossible, to test
Freud's theory was based on the subjective study of single individuals, such as Little Hans, which makes it difficult to make universal claims about human behaviour
The philosopher of science Karl Popper argued that the psychodynamic approach does not meet the scientific criterion of falsification and is therefore pseudoscientific