Freud changed his theories several times over the course of his long career. He initially proposed the seduction theory to explain hysteria, a common disorder of the late nineteenth century involving physical complaints without an actual physical basis. The seduction theory posited that hysteria resulted from early sexual experience, what we would now call childhood sexual abuse. This explanation was abandoned in the late 1890s, however, and Freud focused instead on unconscious sexual fantasy. In other words, the symptoms were caused by the patient’s disguised wishes rather than memories of real events. Freud also moved from a topological theory, focusing on the relationship between conscious and unconscious processes to a structural model, focused on the id, ego, and superego. Finally, in the 1920s Freud added the instinctual force of Thanatos, the death instinct, to his theory of instincts.