I agree with much of what has been presented here, except that INFJs, from what I've experienced & read, do not have the ability to be objective. I have to go against my private, independent nature, and bounce things off of types I know have objectivity as a strength, because I realize that my instincts are not always correct, and I base everything on how it "feels" to me.
Ti is an INFJ's third function.
From what I've read, it is not objective. I don't have enough knowledge on the function to say why, except that from my own understanding, all introverted functions are subjective and all extroverted functions are objective. So, in that way, you're right.
But if that's true, then...
Ni- subjective
Fe- objective
Ti- subjective
Se- objective
However, assuming that I am an INFJ, I do try to do what I think of as objective.
The way that I try is to think of things in my head and consider how I feel about something to be irrelevant.
I do not think that feelers are incapable of that simply because they are feelers. That's like saying that thinkers are incapable of having feelings.