Differences from Jung
Judgment vs. Perception
The most notable addition of Myers and Briggs to Jung's original thought is their concept that a given type's fourth letter (J or P) is determined by how that type interacts with the external world, rather than by the type's dominant function. The difference becomes evident when assessing the cognitive functions of introverts.:21-22
To Jung, a type with dominant introverted thinking, for example, would be considered rational (judging) because the decision-making function is dominant. To Myers, however, that same type would be irrational (perceiving) because the individual uses an information-gathering function (either extraverted intuition or extraverted sensing) when interacting with the outer world.
Orientation of the tertiary function
Jung theorized that the dominant function acts alone in its preferred world: exterior for the extraverts, and interior for the introverts. The remaining three functions, he suggested, operate together in the opposite world. If the dominant cognitive function is introverted, the other functions are extraverted, and vice versa. The MBTI Manual summarizes references in Jung's work to the balance in psychological type as follows:
There are several references in Jung's writing to the three remaining functions having an opposite attitudinal character. For example, in writing about introverts with thinking dominant…Jung commented that the counterbalancing functions have an extraverted character.:29
However, many MBTI practitioners hold that the tertiary function is oriented in the same direction as the dominant function. Using the INTP type as an example, the orientation would be as follows:
* Dominant introverted thinking
* Auxiliary extraverted intuition
* Tertiary introverted sensing
* Inferior extraverted feeling
From a theoretical perspective, noted psychologist H.J. Eysenck calls the MBTI a moderately successful quantification of Jung's original principles as outlined in Psychological Types. However, both models remain theory, with no controlled scientific studies supporting either Jung's original concept of type or the Myers-Briggs variation.