Okay. Basically I have seen a lot of threads here where people say stuff like "Well, I am an ENTP with dominant Ni. What does this mean?"
Usually, the reason for this is that someone took a function strength test and ended up delusional - because that's not how it works. Certain functions require certain other functions in order to function (yeah.) and the popular function strength tests are seriously messing up peoples understanding of this system.
I'll now proceed to explain something that is pretty much evident if you do some research on the functions, but which might be too evident to be noticed by most.
Functions work in pairs only.
This is my basic thesis. You'll never, for example, encounter Ni without Se because they require eachother in order to function. One pair of reverse functions is basically the smallest practically applicable unit of psyche.
So to elaborate on this, I will tour you through the four irreducible units that can be combined to build types:
First out are the percieving function pairs, Se-Ni and Si-Ne. Let's call these paradigms. These are the only two possible combinations of percieving functions. There are no other options, and I'll explain why.
First off, sensing and intuition differ from eachother in that sensing presents a single output, while intuition presents several different sets of output.
We'll begin with Se-Ni. Regardless of other involved functions, Se-Ni by itself has a certain dynamic:
Se absorbs information from the outer world in real time. It is a here-and-now function that's focused only on the tangible hard facts of the present experience. For a Se-Ni-type, this Se experience is the axiom. It's undeniable and self evidently real, and when something appears to be false, it has to be tested in Se space in order to be accepted as valid.
Ni, in turn, uses this input and forms a series of interpretations that apply to the present time experience. The forest fire can be interpreted as a horrible catastrophe. It can also be interpreted as a part of a natural pattern that is necessary for the renewal of the forest. It can also be interpreted as a great opportunity for the media to fill an otherwise eventless day with a great scoop. It depends on the perspective, it depends on what you choose to see. Ni aknowledges that, and Ni does not take sides. It just observes the multitude of different possible viewpoints that can be applied to the same single event.
This combination is irreducible. Ne-Ni is impossible, because there are no axioms to interpret, no anchors to reality and no test-space. Se-Si is also impossible, because there are no options, no differing viewpoints, and no possibilities for anything.
Si-Ne is an entirely different paradigm.
Ne sees the external world as full of different alternatives for action. Every single point in real time has a multitude of possible opportunities attached to it. This can be done, or that, or that. While Se sees the present as a singular axiomatic point, Ne sees the many possibilities inherent in every situation.
Si, in turn, is the axiom of Si-Ne types. It records the personal experience of the user into a database of trustworthy axioms. In order to see if a Ne-idea is good or not, the idea is compared to previously established Si. The difference from Ni is that Si saves only the personal interpretation of every event. It results in one singular world view, in contrast to the wider interpretative space of Ni.
So, in short:
Ni-Se results in One external reality as the axiom, and many possible personal interpretations of every situation. Ni-Se types are experiencer-interpreters.
Ne-Si results in Many external possibilities, and one personal interpretation of every situation. Si-Ne-types are hypothesiser-axiomatics.
On top of these two possible paradigms are the value systems - the Judging functions.
There are really only two possibilities here as well: Fe-Ti and Te-Fi. No other combinations are possible. The Ji function acts as an internal compass, and the Je-function as a way to handle the external world.
The first combination is Te-Fi:
Te: Extraverted thinking cares about one thing: External measurement based on previously established criteria. A Te-judgment can be reduced to this form:
if (criteria is fulfilled) do X, else, do Y
Usually the judgments are more complex, and have several separate criteria with different consequences, but that's the basic form. The formulation of the criteria is a combination between all applicable functions, but Te alone sees if the criteria are fulfilled. It's very binary, black and white and absolute.
Since Te is an external judgment system it drives to apply itself to the external world in one way or another. This might be in the form of a organisational system, the formulation of a scientific theory or a set of legal rules. One can recognize the influence of Te by checking for clearly established, measurable criteria as the basis for one judgment or another. The legal system is a clear example, as well as the scientific method.
Fi, in turn, works in tandem with Te. It's an internal value system that checks for ethical inconsistencies in ones own actions. The ethical judgment is internal, personal and it does not need to be applied to the world. Since it's an internal judging function it has no need for external validation or evidence. It knows that it's right. One has to be responsible for ones own actions before oneself.
Fi sees so that Te states criteria that are ethically correct, according to ones own values.
The second possible combination of functions is Fe-Ti. This combination differs hugely from Te-Fi. (I am a Te-Fi user myself, so forgive me if my Fe-Ti-description is lacking)
Fe, like Te wants to apply itself to the external world. The difference between the two is that Fe wants to establish common ethical values, while Te wants to externalize common systems of criteria and consequence. If Te wants to establish uniform systems of organization to be followed by many, Fe wants to establish uniform systems of values and ethics to be followed by many.
Ti wants to understand the structure of a system. By itself it cares about logical consistency and little else. It can see if something makes sense. Ti users search for logical consequence, and want to establish singular definitions of everything in order to structure their understanding of reality. These singular definitions are necessary in order to be able to follow unbroken chains of reasoning to the very foundations of a system. If Te is induction, Ti is deduction. It reasons it's way to the baseline - what HAS to be the absolute truth in this?
A stereotypical application of the combination of Ti and Fe is the ethical system. Logical systems for externalizing ethics, like Kant's categorical imperative are no doubt a result of this combination of functions.
So, to recap once again:
Te-Fi results in application of rationality to the external world, in combination with an internal ethical compass.
Ti-Fe results in application of common values to the external world, in combination with internal logical reasoning.
This gives us four basic building blocks: Two perceptual paradigms, and two systems of judgment.
To restructure the temperament system a bit, I would like to firstly divide the types according to the perceptual paradigms:
NJs and SPs are Experiencer-Interpreters. (Have Ni-Se)
SJs and NPs are Hypothesiser-Axiomatics. (Have Si-Ne)
and then according to judgment systems:
TJs and FPs use Te-Fi.
FJs and TPs use Ti-Fe.
A result of this is that there are basically four possible combinations of functions in any type, before function order is established:
Ni:Se:Ti:Fe (NFJ, STP) Experiencer-interpreters with external values and internal logic.
Ni:Se:Te:Fi (NTJ, SFP) Experiencer-interpreters with external pragmatism and internal values.
Ne:Si:Ti:Fe (NTP, SFJ) Hypothesiser-axiomatics with external values and internal logic.
Ne:Si:Te:Fi (NFP, STJ) Hypothesiser-axiomatics with external pragmatism and internal values.
I believe that these are the four basic worldviews. Function order only determine priorities, but these four combinations dictate what perspective one takes on the world.
This is why I say other combinations of functions are impossible, and that function strength tests are only throwing wrenches into our understanding of this system.