Maintains-Balance is the condition that a dynamic process respects the modal structure of being. It ensures that a transformation preserves the distinction between what must be and what may be — that directed evolution does not collapse the modal geometry.
Maintains-Balance bridges Movement II: Structural Stabilization and Movement III: Directed Dynamics. Once the modal structure (Must and May) has been established through stabilization, directed motion must be expressed without collapsing it. A dynamic process that maintains balance evolves the system without distorting the distinction between necessity and possibility.
In practice, maintaining balance means that applying the dynamic and then extracting necessity yields the same result as extracting necessity and then applying the dynamic — and likewise for possibility. The operations commute. This is the key constraint on Flow: it is the formal content of the law that flow preserves the modal core.