In order for a human psyche to be able to function at all at the most basic level, they must address the four considerations:
Perception - They must have a way to take in information
Discernment (Or Judgment as MBTI calls it) - A way to make decisions (make sense of information)
Objectivity - A way to address the Outer world
Subjectivity - A way to address the Inner world
You can address these four considerations with just one side of the Psyche, for instance Ti will address Subjectivity and Discernment, and Ne will address Objectivity and Perception.
Now we go a little deeper into advanced functionality:
Humans also need to address the Four Priorities of the Psyche.
Compass Bearings (Subjective Discernment) - They need a way to make decisions based on personal and subjective criteria. Fi and Ti address this Priority.
Stimulus Register (Objective Perception) - They need a way to take in information as it's occurring in the present and Outer/Objective world. Ne and Se address this Priority.
Worldview Map (Subjective Perception) - They need a way to take in information that's personal, subjective, structured and time based (Beginning-middle-end). Ni and Si address this Priority.
Dynamics Mover (Objective Discernment) - They need a way to be able to make executive/Action-taking decisions as well as sense of the dynamics that are occurring in the outer world, how things should be done, and what it means when certain events occur. Fe and Te address this Priority.
Lastly there is the question of what kind of information we're taking in, and what the criteria is for these decisions to be based on. For that, there are 4 channels that all functions communicate through that all humans must also address in some way, two discernment channels and two perception channels.
Interpretive Perception - All humans need a way to receive pattern-based information. Ne and Ni are Interpretive Perceptions
Literal Perception - All humans need a way to receive Concrete and detail based information. Se and Si are Literal Perceptions.
Note: Despite the Jungian naming conventions, Se and Si actually have nothing to do with the senses, they take in literal information, not sensual information. Sensual information is received by both Stimulus Registers including Ne when a person doesn't have Se as a conscious function.
Logic-Based Discernment - All humans need A way to make Decisions based on Logic and/or systemic consistency.
Values-Based Discernment - All humans need A way to make Decisions based on Values.
A person cannot function if they don't have all four 4 considerations addressed on both sides of the psyche, all four Priorities address, and all 4 Perception and Discernment channels addressed. Furthermore, in order to function a person ONLY needs these 12 elements addressed at the
conscious level, no more and no less is necessary.
Let's use an Example: Ti-Ne-Si-Fe
Ti: Addresses the Considerations of Subjectivity and Discernment. Addresses the Priority of Compass Bearings. Provides a way to Make Logic-Based Decisions.
Ne: Addresses the Considerations of Objectivity and Perception. Addresses the Priority of Stimulus Register. Provides a way to receive Interpretive Information.
Si: Addresses the Considerations of Subjectivity and Perception. Addresses the Priority of Worldview Map. Provides a way to receive Literal Information.
Fe: Addresses the Considerations of Objectivity and Discernment Addresses the Priority of Dynamics Mover. Provides a way to make Values-Based Decisions.
Did you see that? All Considerations, All Priorities, and All channels were addressed with just these four Functions, anything more would be unnecessary. This also tells us one more thing, The cognitive functions MUST be ordered in ways that are conducive to the prerequisite Considerations, Priorities, and Channels that humans need to function. This is why you will not see a creature with Te-Ne-Si-Ni; They are not addressing the Four considerations on both sides of the Psyche, and they're missing a Compass Bearings, which is why this creature does not and could not exist.
When you expect that Cognitive configurations (Personality types) exist, then you also expect that there must be a certain logic and structure to the way humans are designed. People on forums like to believe "I use all eight functions in random order and whenever I want, YAAAAAAYY!!" but if you're going to believe that these 16 configurations exist in the first place, then it must stand to reason that there is a certain mathematic to how they're configured that cannot be contradicted. If it didn't work like this, there would be no 16-types, it'd all just be chaos.
The next element of human design that's relevant to this topic is the fact that humans come Off-balanced, this is another design that was done purposely and cannot be any other way. All functions don't have an equal presence and purpose in the Psyche, there is a hierarchy to them. It's a misconception among Jungians or MBTIers alike that having Off-Balanced functionality is a flaw, it's actually great. The Leader-Subordinate relationship among the hierarchy of functions is actually a way more efficient design than supreme equality. Also, being completely balanced would defeat the purpose of having Cognitive Configurations in the first place. So this design is what equips us with Four Conscious Functions consisting of two Momentum and two Modulation functions, and Four Unconscious Functions.
Momentum - These are your top two functions in your configuration. You can think of the Momentum functions as the gifts that keep on giving. They're fast and easy for a person to use, and when used they give a person energy and stimulation. They have an innate drive to keep doing more work. There's a Near-side and close feeling to these functions, as they tend to be the most conscious. You could say that it's these two functions that really create the essence of the Cognitive configuration, an INTP just wouldn't be an INTP if it wasn't for their Ti-Ne Momentum.
Modulation - These are the Bottom two functions. The Modulation functions have the ability to "rein in" your momentum functions and cause them to do less work. They use more energy and feel taxing as a result, and wont be used as freely and easily as the Momentum functions. There's a Far-side of the conscious and "reaching across" feeling that comes with the use of Modulation functions, as they tend to be less conscious (more in the background if you will), although they're still conscious functions.
Unconscious Four - the remaining four functions cannot be used by a person, certainly not in the same way that you'll see a type that has said function in their top four will use them. So it's actually most accurate to say that we don't have conscious control over the unconscious four functions like we have of the conscious four. However, that doesn't mean they're completely absent. The Unconscious Four functions exist as concepts in the unconscious mind. Humans were designed to play with other humans, so the concepts of all Functions and Archetypes come prewired. You might not use Te as a Conscious function, but your Ti comes with an unconscious understanding that there's an over all Te to the universe, that everything is a part of one big cosmic system that can be understood. Because of this, you could say that it's these unconscious functions that your Conscious functions call out to.
Okay, I'm not just lecturing for the sake of hearing myself type, I did all of that to set the stage. If everyone else in the conversation wasn't quite up to speed about how the Cognitive Configurations are designed, we should be more or less on the same page now. So now we can start getting into the Nitty Gritty of this discussion.
Why can't an INTP use Fi?
The technical answer is because the INTP doesn't have Conscious access to Fi, what's an even more important question to ask is; Why should they use Fi? The reasoning that seems to be going around is that Personal Values = Fi. While it's true that Fi can be thought of as personal values, it's not true that all personal values = Fi. If an INTP needs to make a decision based on Personal and Subjective reasoning, they'll use Ti, and if they need to make a decision based on Values they''ll use Fe. The truth is, nobody uses functions in isolation, so they would be using an interplay of Ti and Fe anyway. This interplay of decision making processes will produce a result, and that result might even be the same result as a person that used Fi and Te to make that decision, but that doesn't mean they used the same tools.
You should not think of the cognitive functions as their results, like Te = Planning and Organizing, or Fi = Personal values. That's MBTI rubbish. All humans are designed to handle almost anything with their top four functions. So when we say an INTP doesn't have conscious access to Fi, that doesn't mean they cannot have personal values. It just means the INTP doesn't have access to the Fi hardware that performs a specific task in the psyche.
Personal values is simply a result, a result that can be easily accomplished with the Integrity and Code of Conduct that Fe gives a person. Fe is an Objective and values-based decision making function, and very much like Te, Fe will tell you the right way you're supposed to do something. However, it's values-based so Fe will tell you how a good and heroic person is supposed to conduct themselves. This is the exact same values-based language that Fi is speaking, in the same way that Ti and Te both speak the language of Logic. Fe is objective in the sense that it relates to the way human relationships and dynamics play out in an external communal fashion, but that doesn't mean that these values are not personal, per se. Don't forget, Fe is linked to one of the Worldview Map functions, Si or Ni, so the dynamics of how human relationships work is tied to a person's subjective and personal worldview. This is why Values can still differ from Fe user to Fe user, culture to culture.
Nonsense! You could be doing a math problem or thinking about something. At the same time you are aware of your feelings. People doing logical analysis can have a feeling.
Buh? At no point did I say a person can only make Logic-Based or Values-Based decisions, (one or the other). You guys are confusing Feelings in general with Fi, which is a specific function that has a bigger purpose in the psyche than simply being feelings in general. The reality of Cognitive functions is that they're not as isolated as the people in this thread think they are. For example, I don't just have Ti, I have Ti/Fe, it's all one thing, the two processes are fused together and need each other to work. If you have Ti/Fe like I do, then your Feelings are from Fe, not Fi.
The other problem is what I already covered, but I'm going to be a little redundant here because I really want to hammer this point in:
The anecdotal result of functions does not indicate a specific function. So there is no reason to think this: "That customer likes that color. I should get him some. That will make him happy. Am I happy? Gosh, I like fish, but these long hours. Does the good outweigh the bad?" has to be Fi. Yeah sure, a values-based decision of some kind was made in that example, but it could've been Fe in the same way that it could've been Fi,
they both relate to one's feelings.
Yes, I am, but what I wanted to emphasize was how Se or "perception in terms of extroverted non-abstraction" can be easily reflected in reality. The wind I am sensing now, the screen I am looking at now, the continuous beat of my pulse that I'm feeling, the annoying sound that I am currently hearing. I cannot get this from Si nor Ne.
Words, when things don't make sense, you should stop and ask yourself "Why is my logical paradigm detecting this as a paradox?" I can tell you that the reason this doesn't make sense to you is because you've submitted to a specific erroneous assumption: Se must be used to acquire sensual information.
Se is not exclusive to the five senses. The five senses are a function that occurs in all people regardless of what type they are, however different types will
register the information differently. Se registers objectively and real-time occurring information in its literal and concrete form. The five senses is one of the sources that this information can come from, but Se is not the Senses themselves, it is simply the way you acquire what is coming from the senses. Information coming from the Five senses is acquired by Ne if you have Ne as one of your Conscious four functions. That's right, this is Ne coming into my eyes right now, it is Ne that I taste and feel. However, this sensory information is being registered not in its literal form, it is being registered as a pattern, and if I want to identify these patterns as specific things, I'll have to use Si. But thats just me Words, as to whether you are or are not experiencing Se right now depends on if you really are an INTP or not.
If it is not active, then what's the point of it being named as "unconscious?" What is the point of its existence as an unconscious function?
Because even though you don't have conscious control over it, other people do, all eight cognitive functions exist universally and in the collective consciousness of humanity as a whole. Human beings are pack animals, and we are designed to work together and feed off of each other, so these concepts of all human technology exist in all humans either consciously or unconsciously. When you have a hierarchy of 4 conscious functions, you are left with an empty space that these four functions call out to. The existence of Ti implies the existence of Te, and the existence of Ne implies the existence of Ni, and so on and so forth. Right now, I am referring to all of the functions as more than just human hardware, and I'm referring to them as the concepts that exist in humanity and in the universe. When Ti picks up on Principles, then it is looking for the system, Te. When Ne picks up on possibility, then it understands there are greater unknown truths to reality, Ni. We may not have conscious use of all of these functions, but we are designed to unconsciously reach for them in a way.