This paper reclassifies the Black–Scholes equation as a structural necessity of valuation rather than as a contingent market dynamics model. Instead of assuming stochastic price evolution and deriving valuation via no-arbitrage, the analysis proceeds in reverse: it imposes a small set of admissibility conditions—standing preservation under representational redescription, self-financing invariance, locality, continuity, scale invariance, and time homogeneity—and derives the admissible form of the valuation operator. Under these constraints, valuation rules are shown to collapse to a unique second-order parabolic differential operator, which in standard market coordinates coincides with the constant-coefficient Black–Scholes operator. Stochastic processes and martingale measures are treated as representational coordinate systems for expressing this invariant structure rather than as ontological descriptions of market dynamics. The framework clarifies why Black–Scholes valuation remains structurally central despite empirical deviations and provides a diagnostic interpretation of common extensions (local volatility, stochastic volatility, jumps) as violations of specific admissibility conditions rather than as refutations of the valuation operator itself. Volatility appears as the unique residual invariant degree of freedom, representing irreducible local uncertainty rather than a modeling choice. The paper is foundational and classificatory in nature. It does not propose a new pricing model or attempt empirical calibration, but instead characterizes the conditions under which valuation is well-defined and representation-independent.