The origins of psychodynamic explanations come from the work of Sigmund Freud who provided an explanation for personality development based on principles related to the dynamic interaction between natural instincts and parental behavior. The main methods employed in researching psychodynamic explanations are case studies and interviews. Freud himself used case studies that were based on interviews with his patients to discover the unconscious motivations for their behavior. On the positive side, interviews do have the ability to delve more deeply into issues so that things like unconscious motivations might be uncovered, which wouldn’t be possible with other methods that only scratch the surface. This is particularly the case when dealing with sensitive issues of the sort being discussed here. It is often suggested that Freud's work is based on pseudoscientific assumptions that are both difficult to prove and to disprove, which has led some to argue that his ideas are purely theoretical and therefore have no evidence behind them.