Tertium non datur

1. Etymology

Tertium non datur (Latin: “a third is not given”) names, in Jung’s reversal of the logical law, the reconciling third—not logically foreseeable—that appears when tension between opposites has been held in consciousness. Related: transcendent-function; symbol; synthesis.

2. Plain summary

Logic’s excluded middle says there is no third between A and not-A. Psychologically, when analysis has constellated the opposites so hard that a union of the personality becomes imperative, intellect’s either/or fails. Nature resolves by an energic, symbolic act—something that expresses both sides, as a waterfall mediates above and below. The “solvent” is irrational: the living symbol / transcendent-function that unites without erasing the poles.

Examples (exhaustive house list for this Index lemma — common tertium-non-datur motifs named across Jung’s essays and standard Jungian lexica; not a claim that Jung’s CW contains only these):
reconciling third; hold opposites in consciousness; logic fails; irrational solvent; waterfall mediation; kinship with transcendent-function / symbol / opposites; union/synthesis of personality as necessity.

3. Academic elucidation

In analytical psychology tertium non datur is the paradoxical third of psychic resolution—companion lemma to the transcendent-function. Lexica (Sharp dedicated head; Samuels via transcendent function) supply paraphrase Do not invent loci.

4. Lexicon

Sharp (1991)

Tertium non datur. The reconciling “third,” not logically foreseeable, characteristic of a resolution in a conflict situation when the tension between opposites has been held in consciousness. (See also transcendent function.) … in a logical antithesis there is no third. The “solvent” can only be of an irrational nature. … she acts symbolically… doing something that expresses both sides, just as a waterfall visibly mediates between above and below.

(Sharp, 1991) — cites CW 14 ¶705.

Samuels, Shorter & Plaut (1986) — no dedicated tertium non datur head; route via transcendent function:

(no head) — house paraphrase: Samuels maps the reconciling dynamic under TRANSCENDENT FUNCTION; may note “none.”

(Samuels, Shorter, & Plaut, 1986) — provisional.

5. CW concordance — sample, not exhaustive

Such a situation is bound to arise when the analysis of the psychic contents… has brought the compensatory or complementary images from the unconscious so insistently before his mind that the conflict between the conscious and the unconscious personality becomes open and critical… It requires a real solution and necessitates a third thing in which the opposites can unite. Here the logic of the intellect usually fails, for in a logical antithesis there is no third. The “solvent” can only be of an irrational nature… she acts symbolically… Just as a waterfall visibly mediates between above and below. The waterfall itself is then the incommensurable third.
(Jung, 1955–1956/1970, CW 14, pp. 494–495, ¶705) Dual transcendent-function / symbol / opposites untouched.

Dual via transcendent-function (TF-1–4 already stamped; no rewrite): 1958/1969 · 1917/1966.

See also: transcendent-function; opposites; symbol; temenos; thinking; coniunctio.

References

Jung, C. G. (1970). The conjunction. In H. Read, M. Fordham, G. Adler, & W. McGuire (Eds.), The collected works of C. G. Jung (R. F. C. Hull, Trans.) (2nd ed., Vol. 14, pp. 494–495, ¶705). Princeton University Press. (Original work published 1955–1956)

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.