Structural Realism Without Ontological Exhaustion (Meta-ontology of realism across scientific domains)

Contemporary debates between scientific realism and anti-realism continue to oscillate between ontological inflation and epistemic deflation, struggling to reconcile the explanatory success of science with principled metaphysical restraint. Scientific theories reliably capture stable structural relations and support robust prediction and explanation, yet claims that such success licenses full ontological access to reality remain philosophically problematic. What remains underdeveloped is a unified ontological framework explaining how realism about structure can be justified without committing to ontological exhaustion, metaphysical totality, or privileged epistemic access. Drawing on the Three-Circle Ontology, this paper articulates a constrained form of structural realism in which scientific realism is preserved at the level of structural constraint while ontological ground remains non-exhaustive and non-representable. The position is not an anti-realist thesis, not instrumentalism, not metaphysical skepticism, and not eliminativism. Its primary contribution is to reframe realism as ontological alignment with stable structural constraints rather than as ontological capture of reality-in-itself, thereby preserving explanatory objectivity while maintaining ontological discipline.