Pneuma (πνεῦμα) — from the Greek pneûma, “breath,” “air,” “spirit,” derived from the verb pneîn (“to blow,” “to breathe”). Across several traditions the term names a subtle, vivifying principle that runs through bodies. In ancient Greek medicine, pneuma is the vital breath drawn in by respiration and carried through the arteries, responsible for an organism’s life and movement. It is in Stoicism, however, that it becomes the central physical concept. For the Stoics — above all Chrysippus, who consolidated the system — pneuma is a fiery breath, an active blend of fire and air, that serves as the vehicle of the logos and pervades all matter completely, occupying the very same place as bodies in a “total blending” (krasis di’ holou): in the image attributed to Chrysippus, a single drop of wine could extend through the whole sea. The cohesion of each thing results from an internal tension (tonos) of the pneuma, a simultaneous double movement of expansion and contraction. Depending on the degree of this tension, pneuma takes on distinct, ordered functions: as mere cohesion (hexis) in inanimate bodies, as growth (physis) in plants, and as soul (psyché) in animals. Thus pneuma and logos name the same immanent rational principle that governs the cosmos. Later, in the New Testament, the term designates the (Holy) Spirit, and the distinction between psyché (soul) and pneuma (spirit) runs through Christian theology, notably in Paul, and echoes in the concept of Geist in German philosophy.
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