I notice that INTP's talk about Ti, Ne and Fe a lot. There's a kind of self-deprecating but indulgent view towards Fe - INTP people are generally open about their development or lack thereof of this function I find.
However I can't remember who it was, Socionics or an MBTI site, that posited that a types "hidden motive" (I think they put it like that) is the 3rd function, that this is an especially sensitive point for the type, and also of fundamental, underlying importance. For example, for an INTJ/INTp this is Fi, and therefore these types would have a strong underlying "moral" or "values" system and need for authenticity and deeper meaning in their relationships with people, etc.
I was wondering how this would play out with the INTP/INTj. I'm not really familiar with the Si function, I find it hard to grasp when I read what it does - "storing information and checking it against past patterns" or whatever just sounds banal, I can't see the overriding importance of that to someone's personality.
But I tried some introspection. One thing that I once read, I think maybe on a Socionics site, was that the INTP/INTj Si is expressed in a concern for taking care of themselves physically - when it's more advanced expressed in working out etc., when less advanced expressed in concern for health more generally - I would definitely say this is an underlying motivation for me. Secondly, it just occurred to me that I need some sort of control over some space I can call my own - and sometimes this develops into the need for a project - I wondered if this could be Si? Finally, I'm pretty conservative in my habits - while I oscillate between different habits I usually feel the need for any particular "way of life" - pastimes, eating practices, dressing, music, hobbies etc. - to be rooted in something I can identify with as part of a "culture" I can relate to, which precedes me. Very strange sounding I know. :s
I think this, precisely because it's such an underlying motivation, might be very hard for INTP's to realise about themselves.
Does any of what I said resonate?