Difference occupies one of the most contested and generative positions in the depth-psychology corpus, functioning simultaneously as ontological category, semiotic operator, neurological fact, and psychological dynamic. Its most rigorous theoretical elaboration comes from Derrida, whose concept of différance reconfigures difference not as a stable opposition between two terms but as the restless, non-originary movement that produces all distinctions while itself escaping presence. Here difference is never simply given; it is deferred, traced, and always already implicated in the logic of the sign and the unconscious. Freud’s archive, as read through Derrida, reveals difference at the heart of psychic inscription itself: no breach without difference, no trace without deferral. McGilchrist approaches difference from a neuroscientific and phenomenological angle, insisting that the difference between cerebral hemispheres is real and consequential — not a matter of separated faculties but of qualitatively distinct modes of world-disclosure. Simondon redescribes difference as the generative disparity that makes perception and individuation possible. Across these positions a central tension persists: whether difference is a secondary product of two prior identities, or whether it is primordial — the unground from which both identity and opposition emerge. The term thus bridges semiotics, psychoanalytic theory, philosophy of mind, and individuation theory, marking the threshold where depth psychology meets structural thought.