Sigmund Freud (1856-1939), Austrian psychologist, working at his desk, artwork. Freud had a large collection of ancient religious artifacts, and is said to have drawn inspiration from them as he worked late into the night at his desk. Freud established the idea that mental disorders could have both psychological and physiological causes. He theorised that the human mind has conscious and unconscious levels, and that unpleasant memories are repressed and stored unconsciously, but still affect the behaviour of a patient. Freud analysed dreams to study the unconscious. He also came to believe that sexual impulses were responsible for irrational thoughts and behaviour (neuroses).