Within the depth-psychological corpus, ‘Two’ is far more than a simple integer: it is the primordial act of differentiation itself, the moment at which undivided unity fractures into relation, opposition, and consciousness. Jung’s foundational treatment in Psychology and Religion establishes the philosophico-mathematical ground: one is not properly a number; Two inaugurates counting, separation, and the uncanny sense that the ‘other’ is simultaneously second and sinister — the binarius of medieval alchemy, associated with the devil and the unpraised second day of creation. This ontological weight radiates through the entire corpus. Von Franz reads Two as the cosmogonic split that makes individuation possible. Nichols, through Tarot’s High Priestess, recuperates Two as the number of life and creative relation, insisting that ‘one alone can do nothing.’ Estés approaches it through mythic psychology: the dual nature of a woman’s psyche, figured as twin sisters, carries an ‘uncanny power’ only when both aspects are recognized and held together rather than divided. The Axiom of Maria, elaborated by Edinger, shows Two as an obligatory transitional moment in the alchemical quaternio — the one must become two before higher synthesis is possible. Campbell finds Two expressed architecturally and ceremonially in pharaonic self-divinization. Across these registers a central tension persists: Two represents both the danger of splitting — alienation, evil, the sinister shadow of the Other — and the irreducible precondition for love, creation, and the conscious holding of polarity.