This preprint derives the minimal structural conditions required for coherent system description under persistence and change. Beginning from a single non-ontological commitment—that distinguishability can persist—it shows that any theory admitting persistence must distinguish between a reversible, pre-commitment regime and an irreversible commitment regime. The derivation stops deliberately at the point where quantification becomes necessary, specifying an intelligibility floor rather than a complete theory. This document advances no positive explanatory claims and introduces no ontological commitments. It is a boundary result, not a thesis.