Three
The number three is considered dynamic, masculine, and associated with movement, time, and fate. In dreams, the number three generally refers to the ego in contrast to the unconscious. It has a flavor of completeness, but often “the fourth” is missing (something unconscious). One could say that the number three represents a dynamic that has not yet been completed or reached rest. (See also Four and Number.)
Dynamic Development
Triads are dynamic and can represent desires, drives, and opportunities for change. The number three is regarded as active and associated with “ideas” and the flow of creativity; it denotes a “development process in time” (Psychology and Religion, par. 180). (The number four is more physical, resting, and feminine, but there is a psychological ambivalence between three and four. See Psychology and Alchemy, par. 31.)
Three is also seen as magical because it is a number that makes something happen. You do something three times, and then the fourth thing happens. This is a well-known motif in folk tales. Three, therefore, represents the energy or time required for a certain outcome (often according to fate). One way of interpreting this is that 1 represents the primal state, 2 is the opening to consciousness or awareness of the conflict, and 3 is the solution (which leads to 4, wholeness). (Compare Two.)
Fate and Time
The three Norns in Norse mythology represent the past, present, and future; they are, of course, mirrored by the three Moirai in Greek mythology. If one dreams of the number three, such as three women, it suggests that one has come to a fateful point and that something inevitable will happen. (See also Nine, “the number of necessity.”)
According to Jungian analyst Kenneth James (on the podcast Speaking of Jung, ep. 56), the number three represents “what we must do.” It stands in relation to seven, which is the completion of the active process; together, they form ten, the number of wholeness, according to James.
Alchemy
Hermes-Mercurius was associated with the number three, representing a trinity; both gods have, in some depictions, been portrayed or referred to as having three heads (for instance, "the three-headed serpent" is an alchemical symbol for Mercurius). As psychopomps, this can be seen as a reflection of the threefold nature of the underworld (compare the three-headed Hekate and Cerberus). Mercurius was said to be trinus et unus (three and one). (At the same time, he shares the "stone's" quadrinity; on the floor of one of Mercurius' temples, there was an image of a triangle within a square; in another text, his symbol was a square within a triangle surrounded by a circle, etc.)
Union of Opposites
The "third" is that which unites two opposites. The union of opposites is not a compromise between the two but something new, a third element; this could be an expression of the transcendent function, in brief, the unexpected solution of the unconscious. (The number three, therefore, can also have a sexual connotation in a broad sense.)
If the third element is not introduced, the conflict between the two cannot be resolved on one hand, or the union will not occur on the other. This is an archetypal idea, for example, expressed in the Catholic Church's concept of marriage. The bride and groom are married "in Christ." The union between the bride and groom is not "real" unless it happens in the third, here represented by Christ. Jung says:
"Since opposites cannot be united at their own level [without a third being provided], a superior third is always needed, in which the two can come together... namely through a symbol..." (Aion, par. 280, 281.)
The Polarity of the Triad
A triad always implies the existence of another, according to alchemy, just as the high implies the low, light implies darkness, good implies evil, and so on. This creates tension, energy, potentiality, and a striving toward wholeness.
Jung emphasizes that if one imagines the number four as a square divided by a diagonal, two triangles are formed, pointing in opposite directions—two triads in opposition to one another. (Archetypes and the Collective Unconscious, par. 426.)
Relatively Whole
The number three can sometimes express a sense of wholeness, but according to Jung, it represents a "relative" wholeness, "because it typically symbolizes either a spiritual (or conceptual) totality, such as the Trinity, or a purely instinctual, chthonic wholeness, as seen in the triadic nature of the underworld gods (the 'lower triad'). Psychologically, however," Jung continues, "if the context indicates that it refers to the Self, it is to be understood as a defective quaternity, or as a transitional state on the way to the quaternity." (Archetypes and the Collective Unconscious, par. 351)
The Number Three and the Number Four
The number three in dreams can represent the fact that "the fourth" is missing. Jung repeatedly returns to this interpretation in Psychology and Alchemy (see "function" in the index). What is missing here is the fourth, the unconscious function, typically represented by a woman in relation to a man. The challenge is to bring in the fourth. The fourth "concretizes" the whole and brings it to rest.
"In psychological terms we can say that when the unconscious wholeness emerges, that is, when it leaves the unconscious and enters the sphere of the conscious, one of the four is left behind, it becomes fixed in the unconscious's horror vacui. Thus, a triad emerges, which, as we know, constellates another triad in opposition to it..." (Archetypes and the Collective Unconscious, par. 426).
"The transition from three to four is a problem..." which recurs in many contexts. (Mysterium Coniunctionis, par. 279) von Franz comments on the circumstance that the fourth (or eighth) remains in the unconscious, stating that:
"... this is actually a good thing, because it means that the flow of life continues and constantly constellates new material and new problems. The whole is never integrated, and if we were to assume that it could be, it would mean that the life process had fossilized." (Redemption Motifs in Fairy Tales, p. 108)