An Introduction to Cognitive Functions

It did occur to me that not everyone speaks fluent MBTI. So if you have no idea what I'm talking about or if you want to know more, this post is for you. I could just refer you to one of the plethora of sources on the internet and call it a day. But what would be the fun in that?

Lets start at the bottom and work our way up.

An MBTI personality type consists of four letters. E or I, extroversion or introversion. N or S, intuitive or sensing. T or F, thinking or feeling. J or P, judging or perceiving. These four letters are the simplest way to express your preferences. With these four letters you can form sixteen types from INTJ (introverted intuitive thinking judging) to ESFP (extroverted sensing feeling perceiving)

Now lets look at what are called "cognitive functions." These are eight different ways the mind processes and gathers information. I'll list them here with simple definitions.

Introverted Intuition (Ni for short): Intuitive perception with a trust and emphasis on the interior world.

Extroverted Intuition (Ne): Intuitive perception with a trust and emphasis on the exterior world.

Introverted Sensing (Si): Sensory perception with a trust and emphasis on the interior world.

Extroverted Sensing (Se): Sensory perception with a trust and emphasis on the exterior world.
         
Introverted Thinking (Ti): Logical judgment with a trust and emphasis on the interior world.

Extroverted Thinking (Te): Logical judgment with a trust and emphasis on the exterior world.
         
Introverted Feeling (Fi): "Moral" or "emotional" judgment with a trust and emphasis on the interior world.

Extroverted Feeling (Fe): "Moral" or "emotional" judgment with a trust and emphasis on the exterior world.

Are you seeing a pattern here? These eight function's can be divided into judging and perceiving functions.
This is the most basic way to think about the functions.

Here's how you get from the four letter type, for example, INFP to cognitive functions.
Every person has four of the eight cognitive functions. They have a version of the N, S, T, and F functions. Each function has an introverted or extroverted version, (Ni/Ne) hence the e or i after the initial letter. (We'll get to why a type is "I" or "E", "P" or "J," in a moment) The four function's that a person possesses are "stacked" based on priority, from most preferred to least.
To figure out which functions a type has and what the preverance stack is, take the first letter, that will tell you whether the type is an "I" or an "E," introvert or an extrovert. Introverts have an introverted function on top of their "stack," and extroverts have the highest preference for an extroverted function.  The functions in a person's stack or stacked in either an EIEI pattern or an IEIE pattern. Introverted and extroverted functions are never placed adjacent to each other. The two middle letters determine the top two functions in your stack. To determine which one is introverted and which is extroverted we turn to the "J" or "P" in your type. A Js highest extroverted function is a "Judging" function (Thinking or feeling) and a Ps highest extroverted function is a "Perceiving" function (Sensing or intuition) 
For example, the INFP. The first letter is an "I" so we know this type is an introvert. It has an introverted function on top of it's stack. The next two letters show what it's top two function's are. Either a feeling function and then an intuitive function or vise versa. Then we come to the "P." This tells us that the highest extroverted function is a perceiving function. If you paid attention before you know that "N" is a perceiving function, thus it must be extroverted and can't be on top because of the initial "I."
From all that we get the first two functions. Fi/Ne but we still don't have the last two functions. Once you know the first two the rest is easy. Each function has an "opposite" function. it's opposite function is extroverted for an introverted function and vise versa. It takes the opposite place in the same "J" or "P" group. For example Fi and Te. Ne a Si. Fi is introverted so it's opposite is extroverted. Fi is a feeling function so it's opposite is it's partner in the same category, thinking.
The dominant function "Pushes" its opposite function to the bottom of the stack while the "Middle" two functions are opposites that sit right next to each other. The INFP has these functions in order, Fi/Ne/Si/Te.

At this point the best thing to do is to list the cognitive functions for all the MBTI types and let you figure out all the rest by yourself.

INTJ=Ni/Te/Fi/Se

ENTJ=Te/Ni/Se/Fi

INTP=Ti/Ne/Si/Fe

ENTP=Ne/Ti/Fe/Si

INFJ=Ni/Fe/Ti/Se

ENFJ=Fe/Ni/Se/Ti

INFP=Fi/Ne/Si/Te

ENFP=Ne/Fi/Te/Si

ISTJ=Si/Te/Fi/Ne

ESTJ=Te/Si/Ne/Fi

ISTP=Ti/Se/Ni/Fe

ESTP=Se/Ti/Fe/Ni

ISFJ=Si/Fe/Ti/Ne

ESFJ=Fe/Si/Ne/Ti

ISFP=Fi/Se/Ni/Te

ESFP=Se/Fi/Te/Ni

Good luck! You'll need it trying to figure out my amateur explanation.