Across the depth-psychology corpus, ‘Mental’ functions as a contested border concept, marking the uncertain territory between somatic process, psychic structure, and spiritual principle. Its valences shift dramatically depending on disciplinary context. In Janet’s tradition, as developed by van der Hart, Nijenhuis, and colleagues, ‘mental’ designates a quantitative economy — mental energy and mental efficiency — whose fluctuation determines the integrative capacity of personality and the vulnerability to dissociation. Here the term is almost hydraulic: mental level rises and falls, constraining or enabling adaptive action tendencies. Winnicott and Klein situate ‘mental’ within a developmental and nosological framework, distinguishing mental disorder as a category irreducible to brain disease, while insisting that psychic health depends on integration processes that have distinctly somatic preconditions. Bion’s proto-mental system dissolves the boundary itself, proposing a matrix in which physical and mental remain undifferentiated — a pre-categorical substrate from which group emotions erupt. McGilchrist and Jaynes approach the term through neurological lateralization and the archaeology of consciousness, treating mental illness as a total world-alteration rather than a discrete malfunction. Aurobindo situates mind as a principle standing above matter and life yet below spirit, one stage in an ascending ontological hierarchy. The persistent tension is between ‘mental’ as a measurable functional parameter and ‘mental’ as an irreducible experiential domain that resists external inspection.