Teamtechnology gives a good account of this.The article also references to PUM II actually claiming that there needed to be some rearranging for Keirsey’s theory to fit:The confusion only arises when one tries to make Jung's theory fit into the framework of temperament. For example, in Please Understand Me, Keirsey starts his description of an INTP with:
"INTPs exhibit the greatest precision in thought and language of all the types; they tend to see distinctions and inconsistencies in thought and language simultaneously. The one word which captures the unique style of INTPs is architect - the architect of ideas..."
From a Jungian perspective, this section is clearly defining INTP in terms of the dominant introverted function: introverted Thinking. The description focuses on the inner world of ideas, thoughts, understanding, and explanations.
The description of ISTP, however, starts with:
"Just as impulsive as other SPs, the ISTP's life is artful action - and action is end in itself. Action for the ISTP is more gratifying if it is born of impulse than purpose. If the action is in the service of an end or aim, let the aim look out for itself; it cannot be allowed to influence execution"
From a Jungian perspective, this section is clearly defining ISTP in terms of the extraverted auxiliary function: extraverted Sensing. The description focuses on action, and the outer (extraverted) world is so pre-dominant that it cannot be influenced by any inner world thoughts. There is no mention, whatsoever, in the ISTP description, of the introverted dominant function: introverted Thinking.In Please Understand Me, Keirsey makes the association between Jungian typology and temperament. However, he does not make a straight association - rather, he:
• points out what he sees as errors in Jung's theory
• states that, to make Jungian typology fit with temperament, it has to undergo some rearrangement (pp29,30)
So, according to Please Understand Me, the two theories cannot be directly put together - Jungian typology has to be changed in some way to make it fit with temperament.
Keirsey expands on his criticism of Jung in Please Understand Me II. For example, on p331, he states that:
"Myers' E-I scale is badly flawed because she inherited Jung's error of confusing extraversion with observation (S) and introversion with introspection (N). And so to make the E-I distinction useful at all, we must define the two concepts, not in terms of mental focus or interest, but in terms of social address or social attitude".
This changes the meaning of the Jungian terms quite radically: social attitude, as appears to the outside observer, is a very different concept to mental focus of cognitive functions. Clearly, when Keirsey refers to "E/I", he means something quite different to what Jung and Briggs-Myers meant. When we talk about extraversion, or the letter "E" in the type code, then it is akin to using the word "trunk" in the US or UK. When we are talking temperament, we mean one thing; when we are talking type, we mean another. Unfortunately, because the same letter is used in both systems, the misunderstanding may not be recognised.