This paper develops an operational separation between content‑velocity—the propagation of particles, field excitations, and information‑carrying signals through spacetime—and metric‑velocity, which denotes structural evolution of the spacetime metric itself. Content‑motion is constrained by local causal structure and bounded by c, while metric‑evolution alters geometric relations without corresponding to localized signal transmission. The framework introduces a substrate‑motion operator acting on admissible metric configurations, together with continuity, bounded‑deformation, and causal‑preservation conditions. It further classifies wave‑like phenomena into content waves, metric waves, and zero/shadow modes, clarifying why structural reconfiguration may exhibit apparent superluminal coordinate behavior without violating relativistic causality. The analysis is structural and kinematic, introduces no new dynamics, and remains fully consistent with general relativity. Its contribution is conceptual: it formalizes a motion‑class non‑equivalence implicit in relativistic physics and provides a unified interpretive structure for cosmological expansion, metric deformation, and coordinate‑dependent effects.
William T. Partin (Thu,) studied this question.