In the MBTI, all types are purposely treated as if the first and second functions of individuals NECESSARILY have opposite directions. This is because those who have designed the instrument believe that pure types will lack a necessary balance between introversion and extraversion, and this will be less healthy. 1
Speaking of the 'pure' type, the authors of 'Gifts Differing' say -
Such cases do occur and may seem to support the widespread assumption among Jungian analysts that the dominant and auxiliary are naturally both extraverted or both introverted; but such cases are not the norm: they are instances of insufficient use and development of the auxiliary. To live happily and effectively in both worlds, people need a BALANCING auxiliary that will make it possible to adapt in both directions -to the world around them and to their inner selves.
This theoretical bias in the MBTI is so strong, and has become so deeply embedded in how the system operates and is understood, that we would venture to guess that most MBTI practitioners never learned about the possibility of 'pure type' in the first place. Or, if they had, they surely no longer give much consideration to how the profiles of pure types may differ from profiles of the others. Even those who once were aware of the distinction come to forget, over time, about the possibility of 'pure' types. As we have shown elsewhere, this accounts for an interesting contemporary confusion about the personality type of Jung himself. Although one camp argues that he was an INTP (ie, Jungian IT) and the other argues that he was INTJ (Jungian IN), both remain unaware - because they are caught up in MBTI assumptions - of the fact that Jung was, ironically, himself a 'pure' type. A person who had introverted thinking and introverted intuition as his first two functions (with the former as dominant at some points in his career, and the latter dominant at other times), Jung was one 'pure' or 'extreme' type who not only lived 'effectively', but also made an extremely significant contribution.