A Brief Introduction to MBTI Functional Theory

I've spent a year now studying MBTI and functional theory, and found it extremely difficult to explain. It all works like a puzzle, but if you don't know the correct terminology, or what all of the terms mean, it can get really confusing. So, this is really just a starter, but I have attempted to provide a brief overview of how this all works. I went into as little of detail as I possibly could.


Different Types of Functions

I vs E
Introversion - orients a function inwardly

Extroversion - orients a function outwardly

N vs S
Intuition - makes connections to form abstract ideas

Sensing - orients the physical world to the mind
F vs T

Feeling - deals with interpretation of morals

Thinking - deals with interpretation of efficiency

J vs P

Judging - thinking and feeling orientation

Perceiving - sensing and intuition orientation

What are the Functions,  Then?

Extroverted Intuition - makes connections to form abstract ideas and puts them forth externally

Introverted Intuition - makes connections to form abstract ideas and processes them inwardly

Extroverted Sensing - orients the physical world to the mind and reacts externally

Introverted Sensing - orients the physical world to the mind and processes it internally

Extroverted Feeling - deals with interpretation of morals, and orients them toward benefiting the common good

Introverted Feeling - deals with interpretation of morals, and orients them toward benefiting an individual's wellbeing.

Extroverted Thinking - deals with interpretation of logic, and orients it toward benefiting the common good

Introverted Thinking - deals with interpretation of logic, and orients it toward benefiting the an individual's wellbeing.

How Functions Apply to Personality Theory and Your MBTI Type
The four letters you get are a code for your function preferences. Here's basically how it works
1. The first letter (I vs E) determines if the dominant function is Introverted or Extroverted.
2. The second letter (N vs S) determines which perceiving function a person prefers - iNtuition or Sensing.
3. The third letter (T vs F) determines which judging function a person prefers - Thinking or Feeling.
4. The fourth letter (P vs J) determines whether the person prefers their judging function or their perceiving function.

So, for example, lets look at an INTP for example, since that is mine.
1. According to the first letter, the INTP is an introverted type and will lead with an introverted function.
2. According to the second letter, the INTP prefers intuition over sensing.
3. According to the third letter, the INTP prefers thinking over feeling.
4. The last letter is extremely important however: it determines whether I "prefer" judging or perceiving; in this case, intuition or thinking. This is trickier for introverts however, because in MBTI theory, the J/P preference is more about outward appearance, and therefore it refers to the auxiliary function on introverts, rather than the dominant. So the auxiliary function is the secondary one. Therefore, the INTP leads with Introverted Thinking (a judging function), and secondarily refers to it's extroverted function, Extroverted iNtuition (a perceiving function).

The Functional Stack
Lastly, you need to get the functional stack.

Dominant Function - this is the function a type leads with. This function is the one that is used so much that it annoys everyone else.
Auxiliary Function - this is a person's secondary function. It is usually utilized to people's tolerance, but may be a little excessive as well.
Tertiary Function - this function develops later and its good use is dependent upon its development (like all functions), but is usually used fairly frequently.
Inferior Function - this function is a type's achilles heel, and its lack of use/misuse will probably wreak havoc in a person's life.

An INTP looks like this:
Introverted Thinking
Extroverted iNtuition
Introverted Sensing
Extroverted Feeling

Notice that the tertiary function is the complete opposite of the auxiliary, and that the inferior function is the complete opposite of the dominant. That is how those work. But I'll leave that there because it's a lot to take in.

In short, though, what that order of functions means is this:

The INTP spends much time contemplating and solving philosophical questions and theorizing abstract ideas. INTPs do not share their opinions quickly (though they typically create them immediately), but will brainstorm possibilities with others. INTPs always seek to find the truth, but might not care to utilize their discoveries. To a lesser degree, INTPs internalize their environments before physically interacting with the world around them. They struggle to regard the values of others when it conflicts with their current definition of the truth, yet are also very conscious of and affected by how they are perceived by others.

Where did I get that from?

The INTP spends much time contemplating and solving puzzles and philosophical questions and theorizing abstract ideas. INTPs do not share their opinions quickly (though they typically create them immediately), but will brainstorm possibilities with others. INTPs are most concerned with and will always seek the truth, but might not care to utilize their discoveries. To a lesser degree of prominance, INTPs internalize their environments before physically interacting with the world around them. They can come to greatly enjoy physical means of connecting with one's body, such as yoga or meditation, though keeping up with such tasks is not in their nature. They struggle to regard the values of others when it conflicts with their current definition of the truth, yet are also very conscious of and affected by how they are perceived by others.

The second one is much harder to read, so be thankful I posted it without all of the colors first. I apologize about that, seriously. But I find color-coding helps to make sense of stuff. I will post up a chart here eventually so that you can see the functional stack for any type you are curious about and stuff like that. But yes, the blue there is everything that comes from auxiliary Extroverted INtuition, the green everything from dominant Introverted Thinking, the red from tertiary Introverted Sensing and the violet from inferior Extroverted Feeling.