Schelling takes from the natural science of his day — particularly Galvani's work on animal electricity and the emerging chemistry of Lavoisier and Davy — the observation that natural processes are characteristically dipolar: positive and negative charges, acid and alkali, attraction and repulsion, excitability and stimulus. Rather than treating these polarities as contingent features of particular phenomena, he elevates polarity to a fundamental metaphysical principle. Nature produces itself through the tension of opposites; without that tension, there is no process, no development, no form.
Each domain of nature — inorganic, organic, animal — exhibits the same polar structure at a higher degree of complexity and self-reference. In inorganic nature, the poles appear as the external forces of magnetism and electricity. In organic chemistry, as the metabolic tension between the organism and its environment. In animal life, as the interplay of sensibility and irritability — the nervous system's capacity to receive stimulation and the muscular system's capacity to respond. The philosophical task is to show that these are not merely analogous but expressions of one and the same dynamic activity at successive levels.
Schelling does not think the philosopher must correct or replace the natural scientist. Rather, Naturphilosophie provides the conceptual framework within which the findings of physics, chemistry, and biology cohere — showing why they all exemplify the same underlying dynamic pattern rather than forming a collection of unrelated disciplines. This is philosophy working alongside science, not above it: taking its results seriously and asking what must be true of nature as a whole if all these results are to make sense together.
The polar-forces framework draws on Kant's Metaphysical Foundations of Natural Science as well as on the contemporaneous electrical and chemical research that Schelling followed closely. The idea influenced Oersted's discovery of electromagnetism and later developments in field theory.