Jung used the term "function" to explain ways we use our brain to gather information and make decisions. Sensing and Intuiting are his "irrational", perceiving, information-gathering functions; Thinking and Feeling are his "rational", judging, decision-making functions.
Jung described our direction and source of mental energy ("libido") as an Extraversion or Introversion "attitude". Since all functions can occur in both attitudes, we end up with eight function-attitudes (a term probably first coined by Henry L. Thompson).
Extraverted Sensing Se; Introverted Sensing Si; Extraverted Intuiting Ne; Introverted Intuiting Ni; Extraverted Thinking Te; Introverted Thinking Ti; Extraverted Feeling Fe; and Introverted Feeling Fi.
Over the next 8 days, we'll go into a little more detail about each of these.
You have access to and use all eight function-attitudes, but they show up differently according to where they are in the hierarchy of your personality preferences.
I got four letters on this test, but I don't remember what they are...
If you have taken the MBTI(r) or another personality type indicator, you probably received a four-letter code. Your type code is short-hand for the type dynamics and patterns that lie within. For example, someone with ESFJ preferences has Fe as their lead, dominant, first function; someone with INTP preferences has Fe as their inferior, aspirational, fourth function; someone with ENTJ preferences has Fe as their demonic, eighth function.
Type describes the patterns that those mental preferences bring to who you are and how you behave. Don't break the code into its segments (e.g. to describe someone as a "Sensor" or a "Feeler"), because it's only the context of the whole type that accurately reflects your personality and mental processes.
I can do all functions equally well
Congratulations! Sadly, you're probably kidding yourself.
The function you develop first as your dominant is usually the one you are most comfortable with and most skilled at. It is also the one that is most under your conscious control. The further we go down the list, the less ability we generally have, right down to the eighth function that we probably use with least effectiveness. Until we become aware of the processes and work at improving them, of course.
Dr. John Beebe, noted Jungian analyst, developed a model where he charted the eight function-attitudes to archetypes. Archetypes are universal images that represent the human experience. He calls the first four function-attitudes ego-syntonic, or experienced as part of the self, and the last four ego-dystonic, or experienced as foreign to the self. In other words, those are behaviors and attributes we may project onto something or someone else without recognizing that they are part of us, inside us.
My favorite Jung quote:
Everything that irritates us about others can lead us to an understanding of ourselves.
Here's an overview of the terminology, and how the functions show up(1).
Understanding what these functions mean for your particular type can have tremendous impact on your personal development, how you deal with stress, with change, your leadership and communication style, and it can certainly improve personal relationships as well. I have found them most helpful in my own analysis of how I dealt with expatriation challenges, and I've successfully used it with some clients as well.
What's the difference between conscious and unconscious functions?
You have the most conscious access to your first two functions. Your preferred functions are what comes most naturally to you. This is you in flow, at your best, on a perfect day, when things come easy. These two functions give you strengths and abilities that you probably take for granted and can't believe others don't have the same. These first two functions are the ones that you will have developed during childhood and adolescence, and - in an ideal environment that nurtured your gifts - got to practice the most.
The third function comes into play in or around mid-life, and the fourth function after that, if at all. This is why we have so many people in "mid-life crisis". It's their third and fourth function demanding attention - a completely normal and healthy process on the road to "individuation", becoming your whole self. Again - once you're aware of your type dynamics, you can start consciously working on developing all functions so you get comfortable using them eventually. With some you may never attain a level of grace, but at least you'll notice when they're working you.
Because guess what: you're not in control of all the functions all the time, some take control of you. Particularly those that are more unconscious. Especially at times when you are sick, or tired, or stressed, or all of the above.
When those unconscious functions take over, and even when you try to consciously use them more effectively, it takes mental effort. When you're stressed, you may feel quite literally beside yourself. "Was that really me?" is a title of a book dealing with type and stress, that's how common that question is.
When you're unhappy with who you are and think you have to change for some reason, you will have to overcome your natural preferences and force yourself. It's not easy pretending to be someone else, and it's certainly tiresome.
Thankfully, type awareness helps. Or as Linda puts it:
"When you know who you are, you are freer to be who you're not."
(1) Understanding Yourself and Others - An Introduction to the Personality Type Code, Linda V. Berens, Dario Nardi