Question: “Why do you have to have two extroverted functions and two introverted functions? Couldn’t someone have all introverted or extraverted functions?”
If you had all introverted functions, you would have very little connection to the world outside of yourself. Logic would only exist within your mind and you wouldn’t reference anything in the external world. You would lose your ability to focus and fail to accomplish much of anything. You wouldn’t notice your surroundings and you would likely experience derealisation, in which you feel as though your surroundings aren’t real, or that you’re in a dream. You might even lapse into mild psychosis.
You would have nothing to root you in reality.
On the flip side, if you had all extraverted functions, you might find yourself incapable of knowing anything real about yourself because you would not introspect:
In that case, you would probably look something like Forest Gump.
Not so sure what it’d look like if you were intelligent and all extraverted functions, but an idiot version would probably do whatever anyone told him, not understand or have any concept of himself, be completely task oriented in the sense that they had to constantly be doing something new etc.
This is one of the reasons that it can be kind of difficult to type characters with mental illnesses –and why I’m always careful to note and consider mental illness as a factor.
Certain mental disorders can literally alter your functions, and this may be permanent or temporary. In my case, it’s temporary and happens during manic and depressive episodes only. Other disorders…not so.
PTSD for instance, is capable of turning any extravert into an introvert –because it has a heavy tendency to feature Si. Unpleasant flashbacks and constant dwelling in the past make it so that a person’s functions may actually change temporarily. I will say that in a lot of cases however, the person’s functions don’t change so much as revert to their shadow functions (emergency backup = using your functions in the opposite order).
In a sense, your true functions remain the same, but you’re using the wrong ones. If you were an extravert before PTSD, there may or may not still be an extravert in there somewhere (depending on the severity of the illness).
Major Depressive Disorder tends to make extraverts withdraw and behave like introverts, but I don’t usually see it create actual introverts out of extraverts. Typically, when I see depressed extraverts, I see them constantly spending time alone, but needing to spend time with people in order to help themselves get better.