The Structural Demon: Constraint, Necessity, and Law-Form in Physics

Philosophy of science increasingly appeals to structural constraints to explain phys ical laws’ form and modal robustness, yet lacks a criterion for distinguishing genuinely constraining principles from empirical assumptions. This article introduces the structural demon, an idealized agent determining admissible law-forms from empirically established structural facts independently of initial conditions. The demon yields an operational crite rion of structural effectiveness and motivates structural necessity governing law-forms prior to particular laws. A case study of Fourier’s heat equation shows how locality, conservation, and isotropy uniquely fix the Laplacian form while leaving a thin empirical residue.