If you're relatively new to personality types, you might be familiar with the Myers Briggs Type Indicator system which categorizes people into one of 16 different personality types. The Myers Briggs system, or MBTI for short, attributes a 4-letter acronym consisting of the following letters to represent a personality type:

1. E or I, for Extroversion or Introversion
2. N or S, for iNtuition or Sensing
3. F or T, for Feeling or Thinking
4. P or J, for Perceiving or Judging

In total you have ENTJ, ENTP, ESTJ, ESTP, INTJ, INTP, ISTJ, ISTP, ENFJ, ENFP, ESFJ, ESFP, INFJ, INFP, ISFJ, and ISFP.

Figuring out your 4-letter type is a good starting place, but that's just the beginning. Each MBTI 4-letter type represents a stack of cognitive functions that influences how different personalities think and act. Because a lot of people are actually mistyped by personality tests, it's really beneficial to learn about cognitive functions, understand how they differ between types, and ultimately determine what your function stack is.

 

Cognitive functions relate to the inner two letter possibilities of the MBTI type. We use perceiving functions, Sensing and iNtuition, to observe and reflect on our experiences and environment. We use judging functions, Thinking and Feeling, to draw conclusions or drive our decision-making processes. All four of these additionally have an external and internal variety. Here's a basic overview (taken from MBTI Fiction):

External Sensing (Se):	living in the moment, being totally aware of your environment
Internal Sensing (Si):	nostalgic, often compares the present to the past, traditional
External Intuition (Ne):	can predict all possible outcomes to a situation, a visionary
Internal Intuition (Ni):	knows things intuitively without evidence, has big ideas
External Thinking (Te):	by the book, organization for efficiency, systematic
Internal Thinking (Ti):	analyzing everything, wants to know how things work
External Feeling (Fe):	adapts to the emotions of others, takes care of them
Internal Feeling (Fi):	strong personal emotions, independent of others
(check out more detailed descriptions here!)

Everyone uses four of these functions in daily life (either Si or Se, Ni/Ne, Ti/Te, Fi/Fe). The order of these functions determines your personality type. The order, or strength of the functions goes as follows:

1. Dominant
2. Auxiliary
3. Tertiary
4. Inferior

Extroverted personalities have a dominant external function (Te, Fe, Se, Ne). Introverted personalities have a dominant internal function (Ti, Fi, Si, Ni).

Judging types (types that end in "J") have an external judging function (Te, Fe) paired with an internal perceiving function (Si, Ni), and Perceiving types (ending with "P") have an external perceiving function (Se, Ne) paired with an internal judging function (Ti, Fi).

Extroverted judging types have a dominant external judging function followed by an auxiliary internal perceiving function. ESTJs for example have dominant External Thinking (Te), followed by auxiliary Internal Sensing (Si).

On the converse, extroverted perceiving types have a dominant external perceiving function with an auxiliary internal judging function. ESTPs for example have dominant External Sensing (Se) with auxiliary Internal Thinking (Ti).

The tertiary function is just an inverse of the auxiliary function, and the inferior is the inverse of the dominant. Because the ESTJ starts with External Thinking and Internal Sensing, the tertiary function is External Intuition and the inferior function is Internal Feeling. Following the pattern for the ESTP you get Se Ti Fe Ni.

 

While each of the functions has defining characteristics, they behave differently in different positions. Dominant Fi will share a resemblence with Inferior Fi, but there a noticeable differences between an ISFP personality (dominant Fi) and an ENTJ personality (inferior Fi). Understanding these differences will aide you in finding strengths to leverage and weaknesses to develop (both in you and in others!).

 

Well if you haven't figured it out yet, MBTI Fiction is a good place to start reading. They have plenty of information on what the functions are, in addition to character typing in books, movies and TV shows. Sometimes it's fun to scroll through the different types and see who is what :)

Was That Really Me? by Naomi Quenk is an excellent collection of interviews with all of the personality types as well as information on the inferior functions and how each type reacts under stress. I personally gained a lot of insight reading this, not just for my own type, but for others as well!

MBTI Resources is a good compilation of content for each type.