Giannini’s model differs importantly from Myers’ in that it does not restrict us to just one predominant function pair associated with one’s preferred perceiving and judging processes. His model provides a greater degree of flexibility in the developmental expression of type-related behaviors as well as enhanced adaptive power for engaging and responding to our various environments.
Jung’s approach is based on pairs of polarities. Getting eight functions with such a ‘binary approach’ requires three levels of dichotomy. Jung clearly explained his split of the rational functions into two opposite functions and the same for the irrational functions; but he never provided a theoretical context for a third “dimension” of psychological type.