Types, which proposed a concept of psychological types based on introversion versus extraversion, thinking versus feeling as rational functions, sensation versus intuition as irrational functions, and the coexistence of dominant and auxiliary functions. Isabel Briggs Myers and her mother, Katharine Cook Briggs, subsequently extended and codified Jung's ideas into a test for sixteen psychological types, called the Myers-Briggs Type Indicator. In a two-page chart of "Characteristics of Types in High School" (Myers Briggs Manual, Form E 1958), Isabel Myers described the sixteen types briefly. Keirsey recognized these very brief sixteen descriptions as being accurate, mirroring his observations as a school psychologist, and used these descriptions as a basis in a greatly expanded and modified form of his own. Keirsey's critical innovation was organizing these types into four temperaments and describing "observable behavior" rather than speculation about unobservable thoughts and feelings. Keirsey provided his own definitions of the sixteen types, and related them to the four temperaments based on his studies of five behavioral sciences: anthropology, biology, ethology, psychology, and sociology. While Myers wrote mostly about the Jungian psychological functions, which are mental processes, Keirsey focused more on how people use words in sending messages and use tools in getting things done, which are observable actions. Keirsey performed an in-depth, systematic analysis and synthesis of aspects of personality for temperament, which included the temperament's unique interests, orientation, values, self-image, and social roles. Keirsey's theory blended the sixteen Myers-Briggs types with Ernst Kretschmer's model of four "temperament types", which Keirsey traced back to the classical Greek philosophers, Plato and Aristotle, as well as other ancient writers. Myers grouped types according to dominant cognitive function, as follows: Introverted Thinking: INTPs and ISTPs Introverted Intuition: INFJs and INTJs Introverted Feeling: INFPs and ISFPs Introverted Sensing: ISTJs and ISFJs Extraverted Feeling: ENFJs and ESFJs Extraverted Thinking: ENTJs and ESTJs Extraverted iNtuition: ENFPs and ENTPs Extraverted Sensing: ESFPs and ESTPs Keirsey, however, influenced by Kretschmer's types (Hyperesthetics, Anesthetics, Melancholics, and Hypomanics), grouped the types differently, arguing that the four NFs (iNtuitive/Feeling types) were Hyperesthetic (oversensitive), the four NTs (iNtuitive/Thinking) were Anesthetic (insensitive), the four SJs (Sensing/Judging) were Melancholic (depressive), and the four SPs (Sensing/Perceiving) were Hypomanic (excitable). At the time (mid-1950s), Keirsey was mainly interested in the relationship between temperament and abnormal behavior, finding that Ernst Kretschmer and his disciple William Sheldon were the only ones who wrote about this relationship. ADHD controversy As a clinical