Chapter 1 introduction: definitional and historical considerations, and canada"s mental health. System psychopathology the field concerned with the nature and development of abnormal behavior, thoughts, and feelings, or mental disorders. When studying abnormal psychology you need to remain objective. What is abnormal behavior abnormal behavior patterns of emotion, thought, and action deemed pathological for one or more of the following reasons: infrequent occurrence, violation of norms, personal distress, disability or dysfunction, and unexpectedness. Our best definition of abnormal behavior includes such characteristics as statistical infrequency, violation of norms, personal distress, disability or dysfunction, and unexpectedness. One aspect of abnormal behavior is that it is infrequent normal curve as applied in psychology, the bell-shaped distribution of a measurable trait depicting most people in the middle and few at the extremes. An assertion that a person is normal implies that he/she does not deviate much from the average in a particular trait or behavior pattern.