n. The hypothesis, original with Pythagoras and Plato, of a force (anima mundi, or soul of the world) immaterial but inseparable from matter, and giving to matter its form and movements.n. The theory of vital action and of disease propounded by the German chemist G. E. Stahl (1660–1734); the theory that the soul (anima) is the vital principle, the source of both the normal and the abnormal phenomena of life.n. The general conception of or the belief in souls and other spiritual beings; the explanation of all the phenomena in nature not due to obvious material causes by attributing them to spiritual agency.