Modality Without Possible Worlds: A Constraint-Based Ontology of Possibility

Modal metaphysics continues to rely heavily on possible-worlds semantics or primitive modal facts to account for possibility, necessity, and counterfactual dependence. At the same time, scientific and explanatory practice routinely employs modal reasoning-through laws, counterfactual analysis, and dispositional modeling-while prevailing ontological interpretations remain metaphysically inflated or theoretically opaque. What is lacking is a coherent ontological framework that grounds modality without invoking alternative worlds, irreducible modal primitives, or unexplained modal facts. This paper develops a constraint-based account of modality using the Three-Circle Ontology, interpreting possibility as structured admissibility within an underlying domain of relational constraints rather than as ontological alternatives. The approach does not aim to provide a semantic theory of modality, a reformulation of modal logic, or a dispositional essentialist metaphysics. Its primary contribution is a reframing of possibility, necessity, and counterfactual dependence as expressions of structural constraint spaces that govern admissible configurations and invariant relations. This account preserves the indispensability of modal reasoning in science while offering a parsimonious ontological grounding that avoids metaphysical proliferation.