 The history of science is a history of often contradictory or incommensurable theories, each of which is represented in Cohen’s image as a ring. Nonetheless, as scientific, the variety of theories all express the same central, unitary activity of reason: positing hypotheses. Because of this constant unity of scientific reason, a “continuous connection of reason and the fundamental forces [Grundkräfte] of its history is required” (Cohen 1916: 310). By “fundamental forces” Cohen just means Greek  antiquity,[39]  specifically Plato: