I found this recently and couldn't find it discussed here.
I know socionics is a little bit different than MBTI but I would have to say of the types that I know, it is pretty much spot on. What say you?
Type and the hidden agenda
Aight, bro, it goes like this. In MBTI we've got functions that go like this:
(We'll use the ISTP as an example): Ti-Se-Ni-Fe-Te-Si-Ne-Fi
So technically, the ISTP is a reverse ESTJ or a mirror ESTJ. Its functions mirror this type exactly except they're backwards. This would be the function order if you used all eight cognitive functions to type a person.
So Fi is last and the most foreign to the user. Therefore it is buried in the subconscious and unable to be used. That doesn't mean it can't be used, just that it isn't used. You could say the second you reach the dividing mark between Fe and Te (in the diagram above) the functions become steeped in the unconscious. (No, subconscious and unconscious are not interchangeable terms.)
You could think of these functions as the background tasks on the computer. The things that run in the background without you ever checking them. They run regardless if you want them to or not. Whereas the main four you have allow you to dissect and use them in a conscious way (deliberately, i.e.). You could also think of it like an iceberg if you like. The main four functions make up the top of the iceberg, and the rest make up the bottom.
So to identify what their hidden agendas are, you just have to look at their last function. Their very last function. They're called hidden either because they're buried in the unconscious or because you don't know about them (as in, you won't acknowledge them in your conscious). They're not dangerous or evil. They're just not fulfilled yet.
This by [MENTION=35]snegledmaca[/MENTION] is a good explanation:
ENTp, ESTp : behavior aimed at showing how popular and liked by the crowd you are, but that is actually making you look like an ass.
INFp, ISFp : unshakeable and stubborn defense of ideas and beliefs against all opposition, with unwillingness to even discuss the possibility of their not being correct
INTp, ISTp : unshakeable and stubborn unwillingness to compromise on personal behavior and principles against all opposition in a social situation
ESFp, ENFp : behavior aimed at showing how competent you are in handling practical and financial affairs, or in how much knowledge in a particular subject you have, but painfully focusing on non-essentials to the point made
ISTj, ISFj : unshakeable belief that you know exactly what is going to happen in your life in a given situation, or precipitated action since you know that "now is the time to act", but ending up shooting your own foot in both cases
ENTj, ENFj : behavior aimed at showing how successful, rich, or physically strong and brave and confrontational you are, when others can see you're none of them
INTj, INFj : showing off how wiser you are than others in taking care of your health by good food and avoiding personal risks, but making you look like a paranoid pussy-wimp. Also, an essentially unphysical person trying to show off how they master daily details in administration, maintainance, housekeeping, etc
ESTj, ESFj : behavior aiming at showing how original and creative you can be, but making too much out of obvious and trivial ideas.
Let's go with INFJ. ENFPs are the opposite of this type. Si is their inferior. So therefore, an INFJs eighth function would be Si. Theoretically, of course.
Taking care of your health is a classic example of using Si. Inferior Si is awful - if you don't know how to use it correctly, you could end up overestimating a lot of things.
The best thing to do is memorize charts like this:
ISFJ - Si-Fe-Ti-Ne > Se-Fi-Te-Ni
OR Ne-Ti-Fe-Si > Ni-Te-Fi-Se
This shows you how ISFJs are duals of INTJs. (And by duals I mean opposites, you know.) All you have to do is reverse the functions.
You could also think of the eighth function as a type of animus. Whereas Jung or other theorists would call inf Ne in an ISFJ the animus since it is the lowest function and therefore the driving function of the first, Ni would be the super-animus since it's the very last and completely reverse of the aforementioned animus. Sort of like what an ISFJ might lack. Ne, and especially inferior, makes you paranoid about the future because you visualize all the different outcomes and can't pick one. Ni would calm that down. It would make you pick one. Even if it was wrong, it would still be one as opposed to like a hundred and one.
What you posted about the descriptions is right, it's just very general. You just have to know how the functions operate in order to get it. For instance, let's take ISFJs and INFJs from your description.
Ni would make an ISFJ understand deeply, whereas Ne for an INFJ would make them understand in-depth. They are two different things. I've heard Intuition described as a pool of water, and INFJs search deeply, diving deeper and deeper until they find the answer. An ISFJ or Ne dom would search the surface of the water, going around and around in circles until they explored more or even all of the pool. Ne would give INFJs context. Understanding is worth nothing if it's floating out there in the void. Ni would give ISFJs something to stick to. A place to apply their understanding to - a purpose.
You've gotta kinda take these metaphorically.
As for one more example:
ESTJs and ENTJs and
This is just Fe and Fi. Fe wants to be loved. That is the definition of Fe. Fi users love themselves. They understand themselves. They are comfortable with themselves. Fe projects an atmosphere of warmth that's kind of like a radio tower - if you love, you will get love back. It's not that Fi users can't love, it's just that they don't love outwardly. It's like
this, really. Fi users are selfish in that they can be inconsiderate of themselves. They work hard, almost into the ground. Fe users work to serve other people. If there's no people to serve, why should they work? That kind of thing.
tl;dr we all want what we can't have.