Isabel Myers' type descriptions and David Keirsey character descriptions have several differences between them. One of the primary differences between the two models is that Myers was primarily focused on how people think and feel whereas Keirsey is focused more on how people behave. Keirsey notes that one can not directly observe that people think or feel.
A second important difference is that the Myers used a linear four-factor model in her descriptions whereas Keirsey uses a systems field theory model in his descriptions. A third important difference is the emphasis Keirsey and Myers place on certain dichotomies or preferences. Keirsey believes that whether someone is observant or is introspective is a much more important distinction than whether someone is expressive (somewhat correlated to extraversion) or attentive (somewhat correlated to introversion). On the other hand, Jung, and hence Myers, placed the most emphasis on whether or not someone is extraverted or introverted. A fourth difference is the difference between 'function attitudes' in Myers-Briggs and temperament types in Keirsey’s models.