Franz von Baader’s short essay Ueber Starres und Fliessendes (1808), here introduced and translated by Alberto Bonchino, explores the dynamic relation between rigidity and fluidity as fundamental opposites within both physical and metaphysical life processes. Written during Baader’s collaboration with Schelling and Ritter in Munich, the text belongs to the speculative context of Naturphilosophie and early medical theory, seeking to integrate empirical observation with theosophical reflection. Baader interprets the solid and the liquid not as static material states but as symbolic expressions of the separation of form and matter—conditions that mark death rather than life. True vitality, he argues, emerges only from their synthesis into a “third” principle, in which continuity and penetration coexist as the unity of spirit and nature. This principle, mediating between the physical and the divine, anticipates later Romantic theories of organic life, disease, and moral evil as disruptions of cosmic balance.