While many personality tests tend to categorize conscious elements of personality, what made the psychoanalytic theory of Sigmund Freud and Carl Jung unique was that it focused on the unconscious element. Carl Jung's 1913 work, Psychological Types, was particularly important and influential. Post-Jungian psychoanalysts influenced by Jung's work went on to develop the concept of the "inferior function." This concept was developed in works like the 1971 work by Marie-Louise Von Franz's Jung's Typology as well as Naomi Quenk's Was That Really Me?
But what does all of this mean? First, let us define the four basic preferences of Myers and Briggs personality typing. There are four preferences. The first has as its alternatives Introversion (I) vs. Extraversion (E), the second has as itst alternatives Sensing (S) vs. Intuition (N), the third has as its alternatives Thinking (T) or Feeling (F) and the last has as its alternatives Judging (J) vs. Perceiving (P). Each personality type is a combination of four of these alternatives. For example, the INTP prefers Introversion, Intuition, Thinking and Perceiving. These preferences do not limit the individual to these tendencies, but such preferences tend to predominate as opposed to its alternative.
Four of the eight "preferences" are also functions. Thinking, Feeling, Sensing and Intuition are those 4 preferences. Jung denied that extraversion and introveresion, however, were examples of functions. Instead, they were tendencies to direct our energy either inwardly (as in the case of introverts) or outwardly (as in the case of extroverts). Introversion and extroversion can be combined with functions to produce eight functions: Si, Se, Ni, Ne, Ti, Te, Fi, and Fe.
Like Introversion and Extraversion, Judging and Perceiving are not considered function. This is because Sensing and Intuition already play the role of the "Perceiving" function, with Thinking and Feeling making up the "Judging" function. Sensing and Intuition are means of integrating and synthesizing information, whereas the purpose of Thinking and Feeling is to examine information and make decisions based on the information. Thus, we get 8 functions, which can be further divided up into Judging and Perceiving functions.
-Introverted Thinking (Ti)
-Extraverted Thinking (Te)
-Introverted Feeling (Fi)
-Extraverted Feeling (Fe)
-Introverted Senesing (Si)
-Extraverted Senesing (Se)
-Introverted Intuition (Ni)
-Extraverted Intuition (Ne)
Each personality type has four functions. Functions are organized in terms of the strength the function has within the contexst of the individual's personality, as well as how consciously it is mobilized. The most conscious and most highly developed is known as the "dominant function." They exist in the following order:
1) Dominant function - The most dominant function. We are feeling most at home in ourselves when we are living and moving in this function.
2) Auxiliary function - The second most dominant function. It is the functional co-pilot, so to speak.
3) Tertiary function - This is referred to as "The Adolescent"; it is one of the most underdeveloped functions.
4) Inferior function - This is referred to as the "Child." It is the least conscious and the least developed of thef our functions.
As noted before, each personality type exhibits its own "functional stack." These are each type's four functions. For example, the INTP exhibits the following functional stack:
1) Dominant Function: Introverted Thinking (Ti)
2) Auxiliary Function: Extraverted Intuition (Ne)
3) Tertiary Function: Introverted Sensing (Si)
4) Inferior Function: Extraverted Feeling (Fe)
Note how the functions are ordered according to the relative predominance in this personality type. Sensing (S) and Feeling (F) are not, strictly speaking, part of INTP. However, they do exist as relatively inferior functions (specifically, the Tertiary Function in the form of Introverted Sensing (Si) and the Inferior Function in the form of Extraverted Feeling (Fe)).
Ironically enough, INTP, like IP types in general, have a "Judging" dominant function, such as Ti or Fi. IJs, however, prefer a Perceiving function, such as Ni or Si. Indeed, the dominant function of introverts stand in contradistinction to their J-P designation.
This is the opposite of extraverts, in whose case their dominant function matches their J-P designation. ENTJs, for example, possess the dominant function of Te, which is a judging function, whereas the ENTP possesses a dominant function that is Ne, which is a perceiving function.
The fourth element in each personality type (J-P) refers to the extraverted manifestation of each personality type. Those who possess a J for "Judging" type tend to be decisive and opinionated. Those who are "Perceiving," however, are more flexible and open-minded.
The aforementioned "rules" allow us to make the following correlations between types and functions:
Se - SP types
Ne - NP types
Ni - NJ types
Fe - FJ types
Fi - TJ types
Ti - TP types
Fi - FP types
Si - SJ types
Te - TJ types
Drenth, Dr. A.J. (2014-01-08). The 16 Personality Types: Profiles, Theory, & Type Development (Kindle Locations 84-86). Inquire Books. Kindle Edition.