Every living thing has a Spirit — the puissance of its own soul, and the grip that soul keeps on the world when something from outside pulls at it. Unlike most faculties of the soul it answers to practice. Vigil and fast, meditation, the disciplines a spirit-worker is drilled in, and simply having stood in the dark and held: all of them deepen it.
Spirit is the soul’s defence. Where Will carries a character through fear and Initiative through surprise, Spirit is what stands between them and the forces that want the soul rather than the body.