The consensus in this thread seems to be that it is not possible for a person's type to change. However, all support for this has been given in the form of either a simple statement of belief or a generalization from a particular instance to all instances. Can anyone provide a plausible explanation for why it can't happen? Or even reasonable proof that it can't happen?"
This is a tricky topic. Your four primary function types, especially your first two, pretty much rules out a lot of other types you could be. Granted, it's not always going to be in the same order. My Se scores higher than my Ti sometimes, but the rest of my function order looks ISTPish, and there's no way I'm an extrovert. So no, your function order is not always going to -exactly- line up to your type. What -is not- likely is that an ISTP would have a strong and
healthy Fi or Ne (My 7th and 8th functions).
But completely altering your function order? Now your four primary functions develop throughout life. Keep in mind that as a child, your primary function is really the only one that's developing. So TheChosenOne, for example was primarily an Si child. I can imagine an Si child looking like an ESP, simply because they're craving data all the time. Especially when you're still developing preferences at this time... He was developing both Si and Se, but Si took role of his primary function, and Se as a shadow function to his Si. Next, in your teens, you develop your second function. Your third comes in roughly around your 20s, and your fourth comes in around 30ish or so.
So as a child, it could be possible to switch to another function preference. After all, your primary function is still developing. In your teens, it's a little less likely. 20 and beyond, I think the only way that could happen is if the individual was EXTREMELY undeveloped, underwent
extreme stress, or was in some bizarre accident. And your preference for your dominant two functions would either have to decrease (Very unlikely, as it took your entire life to develop them), or they would stay the same, and relatively weak functions shot up in strength (And be used more positively than negatively). If that were to happen, that would be one badass individual. They'd be more balanced than most, which sounds questionable if the person went through a stressful incident or accident.
Now here's what might appear like a personality change: Your
shadow functions coming out. These are functions 5-8. Unlike primary functions, they usually only show up in negative circumstances (or over a significant period of time as an individual balances out). Under extreme stress, you may live almost entirely in your shadow functions, primarily your more developed 5-6 functions. But they would very rarely be used in a
healthy manner. Now for TheChosenOne, his fifth and sixth functions
are Se and Ti, respectively. So under this period of stress, he looked nearly identical to an ESTP in his late teens. So yeah, of course he would test as an ESTP. Before this stress, he really only depended on his Si + Te. His relief function, or his 3rd function, was barely, if at all, developed. Therefore, once his first two functions were exhausted, he couldn't tap into that 3rd function like an ISTJ in his 30s or 40s could. Instead, he relied on his Opposing function and Critical Parent function (5 and 6... see link above
).
Okay, anyways, in a way, it looked like a personality switch. So I guess if you really wanted to, you could say that he switched personalities for a year. But the fact that he appeared ISTJ again once his stress went away (or once he was able to energize his first two functions again), says that he was doing what any teen would do under extreme stress: Adapt.
Anyways, I'm done ranting now. I would like to add that my ENFP sister thinks I changed personality types when I was around 6-8. I have no idea what I could have been (or what function I was developing), but she says I cried near constantly as a very young kid. I honestly can't remember very much. And I don't know how many Ti dominant children were like that, so I guess she might be right.
But about a year ago, I found a letter from my 6th grade English professor that she wrote to the class and talked about each student. She made note that "And Stephanie's willingness to try anything once." So around 11ish, that sounds more ISTPish