In his clinical observations Freud found evidence for the mental mechanisms of repression and resistance. He described repression as a device operating unconsciously to make the memory of painful or threatening events inaccessible to the conscious mind. Resistance is defined as the unconscious defence against awareness of repressed experiences in order to avoid the resulting anxiety. He traced the operation of unconscious processes, using the free association of the patient to guide him in the interpretation of dreams and slips of speech. Dream analysis led to his discoveries of infantile sexuality and of the so- called Oedipus complex, which constitues the erotic attachment of the child for the parent of the opposite sex, together with hostile feelings toward the other parent. He also developed a theory of transference, a process by which emotional attitudes, established originally toward parental figures in childhood, are transferred in later life to others. The end of this period was makred by the appearance of "The Interpretation of Dreams" (1900), therefore these themes and ideas are prolific within it. However we can also see the early beginnings of his ideas of personality, divisible into the id, ego and superego, and their relationship with the unconscious, preconscious and conscious.