The term ‘dyad’ traverses the depth-psychology corpus along three largely distinct axes, each illuminating a different register of twoness. In Jungian metapsychology, the dyad carries metaphysical weight as the feminine, receptive, and material principle standing in polar relation to the masculine triad — a numerological heritage drawn from Pythagorean and alchemical sources and elaborated in works ranging from Jung’s own ‘Practice of Psychotherapy’ and ‘Psychology and Religion’ to Edinger’s ‘Mysterium Lectures.’ Here the dyad names not a relationship between persons but the ontological character of duality itself: separation, receptivity, the capacity to be formed and impregnated. A second, developmentally focused axis emerges in the relational-neuroscience literature of Schore and Siegel, where the ‘dyad’ designates the caregiver–infant unit as the crucible of affect regulation and self-organisation — the ‘dyadic origin’ of adaptive emotional capacity. Third, clinical and group-process writers such as Yalom deploy the term sociometrically, denoting the bounded two-person alliance within a larger group field, with its attendant dynamics of envy, exclusion, and subgrouping. Hillman, cited by Kalsched, contributes a fourth inflection: archetypes themselves are structured as dyads — paired, dynamic syzygies rather than static images. Simondon adds a still further register, treating the dyad as the polar structure within which a living being orients itself tropistically. The cumulative picture is of a term whose meaning shifts decisively with disciplinary context yet everywhere marks the irreducible tension of two-ness as constitutive of psychic and relational life.