Intellectuals: the NTs
INTJ, INTP, ENTJ, ENTP. Kiersey's overview of the group.
Up side: NTs are idea- and logic-driven. Concepts, structure, and rationalizing come easy to them, and they apply their ideas practically to the world around them.
Down side: They can be socially inept, angsty, and arrogant. Often come across as chilly and indifferent. The more socially adept ones can be very manipulative of those around them. For women of this type, there's the extra challenge of being seen as a "cold-hearted bitch" because our culture expects women to be warm and nurturing.
Dreamers: the NFs
INFJ, INFP, ENFJ, ENFP. Kiersey's overview of the group.
Up side: The combination of Intuition and Feeling makes the NFs a sensitive and idealistic group. They want to communicate, understand, and empathize -- which can be difficult in an ugly world.
Down side: They can fall into their deep interior world of thoughts and feelings, and come across as spineless and out of touch. Men of this type can have an especially rough time, since our culture still frowns on men showing emotions, and they'll be told to "man up" and ignore their natural sensitivities.
Managers: the SJs
ISTJ, ISFJ, ESTJ, ESFJ, aka "the Guardians." Kiersey's overview of the group.
Up side: SJs are solid, reliable, ordinary folks. They get stuff done, they keep their promises, they don't rock the boat unless they feel they must.
Down side: They can be boring, boring, boring. At the extremes, they can be stiflingly straight-laced and dedicated to enforcing their brand of conformity on everyone.
Artisans: the SPs
ISTP, ISFP, ESTP, ESFP. Kiersey's overview of the group.
Up side: In general, the four SP types are people who like to work with their hands, do things, create things. They're practical, but they seek new ideas and fun. Lots of fun.
Down side: SPs can become shallow show-offs and thrill-seekers, either annoying the heck out of people or leaving a swath of broken hearts in their wake -- because all that matters is their own pleasure.
Fleshing out
Most character-generating systems start with the surface appearance and behaviors -- their favorite things, their personal experiences, and such -- and works their way into the character from the outside. Using MBTI takes you in the opposite direction.
We're starting with what makes the character tick, here, and once that's been established you can start working out how a character's MBTI shaped how he experienced his personal history -- what parts of those events shaped him more than others -- why his favorite things are his favorite things.
In fleshing out my characters, I bring world-building and story plot into play here, weighing what the character needs to be with what my creative gut is telling me will be interesting. I try not to "assign" characters an MBTI, especially not major characters, but I narrow it down to two or three most likely and feel my way from there. As the character becomes real, they'll tell me what they are.
MBTI is innate. It's influenced by one's upbringing and maturity level, and if one doesn't have a strong preference in more than one dichotomy, one can be difficult to type -- but in general, your type sticks.
Age and function mastery
As stated earlier, a character's two dominant functions will be the easiest, most comfortable modes of being for him. They are also the functions that manifest at a young age. There's a fair amount of discussion about how children "figure out" what type they are, but in general it's thought that the dominant function has settled in by the time you get to your teenage years.
The secondary function develops over the teen years, which then determines which are the tertiary and inferior functions. Since those two don't come easily to a person, how well they will be developed depends on what effort is put into them -- or not.
Twenty-somethings and those who don't develop further can be stereotypes of their MBTI. NTs, the fumbling nerds. SPs, the party animals. NFs, the starry-eyed idealists. SJs, the goody two-shoes.
The other two functions develop "later in life" (most sources say) which is deliberately vague because there's an element of voluntary effort in there. But as a 41-year-old who has put in some effort, I think I can say I'm comfortable with my lesser functions as an INTJ, and that it happened over the course of my thirties.
Four dichotomies:
Intuitives/Sensors • Feelers/Thinkers • Introverts/Extroverts • Judgers/Perceivers
Intuitives/Sensors • Feelers/Thinkers • Introverts/Extroverts • Judgers/Perceivers