The 3rd & 4th function of MBTI function ordering are simply the shadow of the 1st and the 2nd.
Example of how the Fe shadow of Ti can be seen:
Ti can warn someone else for logical flaws he is about to make
Ti does this purely with the intent of getting rid of flawed logic. not because it wants to help
But it can look like the logical warning of Ti cares/helps/supports like the Fe function.
Thus a Ti-dom will leave traces of Fe in his act. It was never the intent to act Fe (help/support/care), but it looks like that. Thats the shadow effect!
To have dominating Ti, as in an INTP, the person MUST have repressed Fe. As Ti can only be stronger if Fe gets weaker. (This is Jung's definition, they guy who defined the functions you are talking about. You should know what you are talking about).
So Fe should have been defined in MBTI as the last function actually, like on position 8. Then it would have been more Jung-compatible.
But MBTI has just put the shadow of 1&2 in 3&4 because these functions can be observed (as a shadow effect, not with real intent) more than function 5-8. Thus they appear as they are the 3rd and 4th most common functions of that person. There is something to say about that ,as these functions 3&4 can really be observed more powerfully, so their deviation from Jung might have been beneficial in typing people, especially since most people have no clue about the shadow.
But in real Jung language: you do not have a 3rd and 4th function. They are just after-effects (shadow) of your real 1st and 2nd function intent.
The shadow is just something that "happens to a person" without the person ever having had the intent for it.
So INTPs, now you know why others confuse your Ti-warnings for Fe-help: Because the outsider has no simple way of telling what the intent was, both Fe and Ti look pretty similar in a person's outer act. It is only the actor itself that knows the original intent (Fe or Ti), while this intent is a black box (unknowable) for the observer .