So basically what you're saying is that either your perceiving function is most instrumental and serves the judging function. Why can't the dominant function regardless of if it's perceiving or judging be in charge. This is when we need to figure out the difference between type theory and temperament theory because this confuses two different issues.
Here's some info I found about the differences between ISTPs and INTPs.
Confusion of Extraversion with Sensation
Another criticism from the above quotation is that Jung confused Sensation with Extraversion. In fact, this is not true. This misunderstanding probably emanates from either:
- Jung's description of the thought processes he went through before arriving at his final theory. He had, at one point, associated intuition with introversion, but he moved away from that view before arriving at his final theory, or
- a misunderstanding of Jung's use of the term "concrete" in Psychological types. ("Concretism" was a technical term that, according to Jung, reflected a primitive state of a function where it is fused with Sensation, and it results in a person's actions being determined by outer (extraverted) objects. However, the term concretism was not intended under any circumstances to apply to a normal, differentiated Sensing function.)
It is clear, from Psychological Types, that in Jung's final theory, Sensing and Intuition had been completely separated from Extraversion and Introversion, and there was no confusion in his own mind.
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.
Clearly, when Keirsey describes an ISTP he uses terms that are much more 'extraverted', and when he describes an INTP he uses terms that are much more 'introverted'.
By comparison, Isabel Briggs-Myers description of ISTP is written in terms of the introverted Thinking dominant function:
"ISTPs have a vested interest in practical and applied science... ISTPs can use general principles to bring order out of confused data and meaning out of unorganised facts" (p91 Gifts Differing)
In fact, Isabel Briggs-Myers description is in some ways opposed to Keirsey's: whereas he describes them as action-driven, she states that they are "great believers in economy of effort".
Keirsey resolves this difference by stating that Isabel Briggs-Myers "inherited Jung's confusion between Sensing and Extraversion, but in this respect her writings are completely consistent, and she portrays ISTPs as introverts. Keirsey portrays ISTPs in an extravert fashion because his system of temperament is different to Jungian typology - and the use of the same system of letters to describe both is unfortunate because of the confusion it both causes, and hides.