They don't overlap. They encompass different domains. The impersonal vs the personal. People sometimes use "principles" interchangeably with "values", but they are not the same thing in the sense I used them. Establishing something from "first principles" incorporates the "fundamental truths" part of that definition. It is a process of formal logic. If you have trouble conceptualising this difference it seems doubtful you're INTP, since well-developed Ti tends to be highly sensitive to such distinctions.
Read basic definitions of the functions here:
http://www.cognitiveprocesses.com and see if this helps.
And don't get too hung up on typing yourself. It's really not important. There is no scientific basis and no real value in asserting that you
must be one type over another.
Where he/she may have seen the overlap is that both can apply to behaviour for example. When a Ti type works out principles that are then applied to behaviour, what is their motivation? The reasoning process will definitely be impersonal, the underlying motivation behind it may or may not be impersonal. Otherwise I agree with you that an impersonal principle isn't created and viewed the same way as a personal (Fi) one.
Btw, I don't think it's such a good idea to tell someone else what they should find important or not important. Do you really think science is able to cover everything in life? Don't get me wrong, I like the scientific way of thinking, referring to science is just not a good reasoning for attempting to invalidate someone's motivations for understanding something that's currently hard to investigate by hard science.
PS: Don't get me wrong - It certainly took a while for me to understand what it means that science isn't able to explain everything; current scientific methodology is just a way of investigating things, though undoubtedly the most sensible way to go about things. However, it doesn't mean that you can't try to explore things where we don't have a real scientific explanation yet.
This is a (common) misapprehension. Everyone has all 8 functions. No one has ever suggested otherwise. If the weakest function for the INFP is Te (the inferior), it follows that most INFPs will have better use of Ti than Te. (Just as most INTPs will have better use of Fi than Fe). Variance in function development between individuals is considerable.
This isn't just my opinion (see Thompson, for one). Nor is it simply logically obvious (following from the very nature of inferior functions). Empirically it is the case more often than not. It's also the only model in which the INXP type makes any kind of sense. That the Beebe model (Ti+Fe vs Fi+Te) predominates in some circles says nothing about its legitimacy. If you think you can prove its validity, go ahead.
That the bipolarity of the MBTI model is invalid is well established. (Eg see
http://www.ncbi.nlm.nih.gov/m/pubmed/8473967/?i=3&from=/10953511/related).
Singer-Loomis has greater validity (i.e. not a forced-choice model).
Bad word usage, what I meant was INFP doesn't prefer Ti. As for a shadow function being more readily used than the inferior, well I can't say if it has to be that way. Your original statement didn't make sense simply because you also added into it that Ti is "the" logical function (formal logic). INTJ would still have shadow Ti, and it would easily be stronger than INFP's shadow Ti. So if I was going to compare INTJ to a more logical type on the basis of the idea that Ti is more logical than Te, I would have used an xxTP for comparison instead of INFP. That's all.
The only thing I would be willing to claim about INFP vs INTJ is that
stereotypical INFP would be less logical than
stereotypical INTJ. Nothing more, nothing less. (Bolded: for a reason. I am sure there is individual variation.)
Also, I never implied that I believe in any function model, but here we go: I do not. So I don't care about trying to prove the validity of any of these function theories.
Btw, I did not understand what you meant by INxP type making sense only in one model. What to you doesn't make sense about INxP otherwise and why?
I don't know how to answer your other questions, but if you are trying to determine whether you are INTP, I would say it's unlikely. I think you tested as ESTP and that seems like it might be a better fit.
No, I don't think I'm INTP because I'm not into the Ne function at all. I however still have a problem with the ESTP idea because I'm nowhere near as hung up on Se as stereotypical ESTP seems to be. Have you really forgotten that there is another Ti-dom type that's not INTP?
In Mal's test ISTP and ESTP got the same points (a tie, yes), which was pretty interesting.
I was asking you as an INTP because I wanted to see if what I described is part of Ti or not. Did my question not make much sense or why are you not sure about how to answer?