if their behavior is causally determined by forces beyond their control. Behavior is categorized as being either unconscious, environmental or biological by various theories. Heredity (nature) versus environment (nurture) – Personality is thought to be determined largely either by genetics and biology, or by environment and experiences. Contemporary research suggests that most personality traits are based on the joint influence of genetics and environment. One of the forerunners in this arena is C. Robert Cloninger, who pioneered the Temperament and Character model. Uniqueness versus universality – This question discusses the extent of each human's individuality (uniqueness) or similarity in nature (universality). Gordon Allport, Abraham Maslow, and Carl Rogers were all advocates of the uniqueness of individuals. Behaviorists and cognitive theorists, in contrast, emphasize the importance of universal principles, such as reinforcement and self-efficacy. Active versus reactive – This question explores whether humans primarily act through individual initiative (active) or through outside stimuli. Traditional behavioral theorists typically believed that humans are passively shaped by their environments, whereas humanistic and cognitive theorists believe that humans play a more active role. Most modern theorists agree that both are important, with aggregate behavior being primarily determined by traits and situational factors being the primary predictor of behavior in the short term. Optimistic versus pessimistic – Personality theories differ with regard to whether humans are integral in the changing of their own personalities. Theories that place a great deal of emphasis on learning are often more optimistic than those that do not. Personality theories Type theories Personality type refers to the psychological classification of people into different classes. Personality types are distinguished from personality traits, which come in different degrees. There are many theories of personality, but each one contains several and sometimes many sub theories. A "theory of personality" constructed by any given psychologist will contain multiple relating theories or sub theories often expanding as more psychologists explore the theory. For example, according to type theories, there are two types of people, introverts and extroverts. According to trait theories, introversion and extroversion are part of a continuous dimension with many people in the middle. The idea of psychological types originated in the theoretical work of Carl Jung, specifically in his 1921 book Psychologische Typen (Psychological Types) and William Marston. Building on the writings and observations of Jung during World War II, Isabel Briggs Myers and her mother, Katharine C. Briggs, delineated personality types by