There are a few issues here. One is the Jungian theory of types, another is the adequacy of the Myers-Briggs method for applying it, and maybe finally there is what uses people make of the four letters, which neither Jung nor the Myers-Briggs team is necessarily responsible for.
The theory exists independently of the test, and is largely descriptive. There is no reason why anybody, after learning what the six or eight core terms mean, couldn't be very good at classifying people simply by talking with them. In the case of historical figures, if you have good biographical data about them, then you can probably do a good job classifying them at the time for which you have data.
However, whether historical figure or living person, nobody "is" INFJ. It's not a life sentence, at best, it's a snapshot. Iit is hard to think of anything less Jungian than for anybody to identify themselves with a string of letters. Only accidentally would Hitler or Bin Laden "have been" whatever string for a very large proportion of their lives. It's entirely possible that they, like anybody else, might have been that way at some time in their lives, and not at others.
Stance (the first "letter") is a different kind of thing than function (the next two letters, and the fourth letter is an odd way to code something else about a function, and that coding is specific to Myers-Briggs). Stance plausibly is more persistent through life than function. For one thing, it is easily and immediately balanced. If you are a conscious introvert, then there is no problem having an "unconscious extrovert." All that would really need to change in individuation is to become familiar with that other stance which may well already be there anyway.
Function is different. It's skills, two complementary pairs of skill sets. If you have a strongly dominant function, then that's great. That allows you to develop that skill set. The danger, of course, is that you never develop its complement, or perhaps overlook the orthogonal pair as well. Unlike stance, a function you don't develop stays undeveloped.
So, you should change over time. And, unlike stance, you don't have an unconstrained selection about what skills you will need in life. If all goes well, you currently emphasize the function that works best for you in the problems you actually have at the present time. Ideally, you'd have all four functions well developed,whether or not they are in use right now.
Which is another problem with assesment. The Jungian issue is state of development, a matter of potential usefulness. That can be assessed by looking what you actually did recently when confronted by a certain kind of problem you actually had and were concerned with, ideally a problem rich enough to reveal where you are in all four functions (or if the theory is right, where you are in any orthogonal pair). That's an open-ended assessment, and clearly would benefit from the analyst asking focused questions about the specific challenge you faced, and how.
Myers-Briggs doesn't directly assess functional development. It's heavily based upon authobiographical recall, with a hope that your recalled solutuion behavior fairly reflects the underlying state of development. I'm not saying that that's an unrealistic expectation on average, just that it introduces an additional issue besides the Jungian theory of types. For example, the instrument may be assessing what functions you have actually needed to use recently, rather than how developed each function actually is.
Finally, I have less enthusaism for that "horoscope page" than Chloe does. If it worked for her, then that's great. But it doesn't have even the flavor of the Jungian notion of dominant finction. There are reasons why INFP's and ISTJ's (or more generally, same stance, but "opposite" functionality) might not "get along." On the other hand, there is a tremendous opportunity to learn. But do it quickly, since you might present a problem which the other person deals with by meeting you halfway, and develops one of their functions by learning from how you deal with them.
In which case, Uncle Carl would be very pleased.
Edited by eight bits, 04 July 2012 - 07:03 AM.