Primary function

1. Etymology

Primary function (also superior function) is the most differentiated of the four psychological functions—the one used most automatically because it comes most naturally. Compare inferior-function.

2. Plain summary

Society pushes differentiation of the best-equipped or most socially successful function; one often identifies with it—hence psychological types. Decide which of thinking, feeling, sensation, intuition is primary by which is under conscious control vs haphazard. Superior function (introverted or extraverted) expresses conscious personality—aims, will, performance—while less differentiated functions are things that simply “happen.”

Examples (exhaustive house list for this Index lemma — common primary-function motifs named across Jung’s essays and standard Jungian lexica; not a claim that Jung’s CW contains only these):
most differentiated function; superior function synonym; social success differentiation; type formation; conscious control criterion; vs inferior-function; introverted/extraverted modes.

3. Academic elucidation

In analytical psychology primary/superior function is conscious typology lead—CW 6. Descent Press keeps Sharp in §4; Samuels under typology. Prefer CW 6 ¶763; ¶575; dual-stamp IF-1–3.

4. Lexicon

Sharp (1991)

Primary function. The psychological function that is most differentiated. (Compare inferior function.) … The superior function is always an expression of the conscious personality, of its aims, will, and general performance, whereas the less differentiated functions fall into the category of things that simply "happen" to one.

(Sharp, 1991) — cites CW 6 ¶763; ¶575 in Sharp’s lemma.

Samuels, Shorter & Plaut (1986) — no dedicated primary function head; covered under typology (shared with inferior-function):

(See typology.) No primary-function-only head

5. CW concordance — sample, not exhaustive

The demands of society compel a man to apply himself first and foremost to the differentiation of the function with which he is best equipped by nature, or which will secure him the greatest social success. Very frequently, indeed as a general rule, a man identifies more or less completely with the most favoured and hence the most developed function. It is this that gives rise to the various psychological types.
(Jung, 1921/1971, CW 6, p. 623, ¶763) Dual inferior-function IF-1–3 untouched.

We call a mode of behaviour extraverted only when the mechanism of extraversion predominates. In these cases the most differentiated function is always employed in an extraverted way, whereas the inferior functions are introverted…
(Jung, 1921/1971, CW 6, p. 479, ¶575)

See also: inferior-function; fourth-function; thinking; feeling; sensation; intuition; orientation.

References

Jung, C. G. (1971). Psychological types. In H. Read, M. Fordham, G. Adler, & W. McGuire (Eds.), The collected works of C. G. Jung (R. F. C. Hull, Trans.) (Vol. 6, pp. 479, 623, ¶575, ¶763). Princeton University Press. (Original work published 1921)

Samuels, A., Shorter, B., & Plaut, F. (1986). A critical dictionary of Jungian analysis. Routledge.

Sharp, D. (1991). Jung lexicon: A primer of terms & concepts. Inner City Books.