Formal framework identifying structural limits of accessibility, describability, and anticipation across domains of constraint. This article introduces a formal classification framework for regimes of constraint governing the accessibility, descriptibility, and anticipability of systems. Rather than proposing new physical laws, the framework identifies structural thresholds beyond which coherent causal description, optimization, or recommendation becomes illegitimate, even if the system itself continues to exist.We formalize an irreducible alphabet of accessibility states and organize them across orthogonal domains of constraint (geometric, dynamic, informational, thermodynamic, causal, and observational). The resulting “periodic table of constraint regimes” distinguishes between existence and describability, clarifying why persistence, irreversibility, and collapse cannot always be anticipated within a given reference frame.The framework is purely structural and formal: it introduces no empirical assumptions, no ontological claims, and no physical postulates. Its contribution lies in identifying necessary conditions for valid causal description and in delimiting the boundaries of legitimate inference in complex, irreversible systems.