Spiritus occupies a peculiar and generative position in the depth-psychology corpus, functioning simultaneously as a physiological concept, a metaphysical category, and a paradoxical therapeutic formula. The term enters the literature along at least three distinct axes. First, through Ficino’s Renaissance pneumatology, spiritus names the vaporous intermediary substance mediating between body and soul—neither fully corporeal nor fully immaterial—a ‘very subtle body, almost not a body, indeed almost soul,’ as Moore’s readings of Ficino make plain. Second, in the alchemical literature as engaged by Jung and von Franz, spiritus appears as one pole of the classic corpus-anima-spiritus triad, and is frequently conflated with or hypostatized as Mercurius, the spiritus vegetativus, spiritus seminalis, and spiritus Phytonis, each epithet registering a different aspect of animated, world-permeating vitality. Third, and most charged for modern depth psychology, spiritus appears in Jung’s letter to Bill Wilson in the formula spiritus contra spiritum—alcohol (spiritus) countered by spirit (spiritus)—a paradox that Peterson and Dennett each probe as the dynamic core of addiction and recovery. Von Franz develops the pneumatological theology of the Aurora Consurgens into a psychology of the Holy Spirit as the guiding function of the unconscious. Across these registers the fundamental tension is consistent: spiritus is the term that refuses the dualism of matter and transcendence, insisting on the reality of the intermediate realm.