This paper formulates the Structural Admissibility Axiom as a conceptual foundation forDimensional-Structural Describability. The central question is not merely what an observermeasures, but what a descriptive regime can define as a coherent structure. We distinguishobservation from describability and define a structural observer as a restricted structural notion: a set of admissible conditions under which objects, relations, boundaries, continuities,connectivities, separations, admissible directions, domains of assignment, and accessibilityrelations become meaningful.Within this framework, structural admissibility conditions are not additional spatial dimensions, hidden variables, new physical entities, or ordinary dynamical degrees of freedom.They specify the conditions under which a descriptive regime can define structures in thefirst place. The axiom proposed here does not replace existing physical theories. It clarifies aprior layer normally presupposed before theory-specific quantities, coordinates, observables,force components, boundary conditions, or structural comparisons are assigned.The paper also clarifies a point implicit in restricted descriptive-regime thought experiments. Ordinary force composition presupposes that the relevant force components aredefined within the same admissible descriptive regime. If a regime lacks the admissiblestructural condition required to define a given direction, then the corresponding force component is not a hidden internal force and is not a zero component. Rather, it is not awell-defined term of the internal resultant-force description. This distinction is used to illustrate why non-definability should not be confused with non-observation, zero value, hiddenstructure, or an additional physical dimension.The present work is deliberately limited. It does not derive a dynamical law, a propagation constraint, a structural-response law, a quantum measurement rule, or an observationalvalidation. Mathematical functional realization through a weighted structural descriptor,time-dependent structural reorganization, structural information propagation, structuralresponse applications, and observational or computational consistency checks belong to subsequent developments.
Dominicus Kwon (Tue,) studied this question.