Cognitive therapy is a form of psychotherapy in which the therapist tries to teach the patient to think more rationally. In mild to moderate cases of depression, cognitive therapy seems to work as well as antidepressant medication. Yet like any other form of psychotherapy, cognitive therapy seems to be less effective for people with more serious mental illnesses. These findings would come as no surprise to an ancient Greek or Roman physician. Cognitive therapy is really just coaching in logical thinking. Ancient Greeks and Roman philosophers believed that logical thinking is an art that can be cultivated. However, they also recognized that some people have medical problems that make it difficult or impossible to think logically. In Roman law, a person would not be held legally responsible for an act that was committed when he was not in control of his mind (non compos mentis).