When Is Ontological Suspension Legitimate? Newtonian Restraint and Quantum Understanding

Abstract

Quantum mechanics is often presented through a forced choice: either a physical theory becomes intelligible only after it specifies what reality is intrinsically, or predictive and operational success is all the understanding physics can legitimately seek. This article rejects that choice. Newton's treatment of gravitation shows how a theory may provide substantial physical understanding by identifying mathematically articulated dependencies, unifying phenomena, and supporting counterfactual reasoning while leaving the underlying mechanism unsettled. Yet Newtonian restraint was not a prohibition on why-questions. It was a rule for withholding answers that could not be inferred from the phenomena while keeping causal inquiry open. On this basis, the article develops a criterion of calibrated ontological suspension. Suspension is legitimate, relative to a specified explanatory task, when the theory supplies adequate dependency structure, rival ontologies remain evidentially underdetermined, the unanswered ontological question is not constitutive of the explanandum, and the suspension remains revisable. It becomes illegitimate when the missing commitment changes what counts as an outcome, a mechanism, a domain of application, or a solution to the problem posed. Applied to quantum mechanics, the criterion yields a differentiated verdict. Interference, probabilistic constraints, symmetries, and no-go theorems afford genuine structural understanding without a complete intrinsic picture; indeed, no-go results sharply restrict admissible ontologies. By contrast, in the measurement problem, determinate outcomes are part of the explanandum, so their status cannot simply be bracketed. Decoherence explains stability and suppression of interference but does not by itself select a single outcome. The proposal is therefore neither a new Copenhagen interpretation nor an instrumentalist dismissal of ontology. It is a methodological account of when ontological incompleteness is compatible with, and when it obstructs, physical understanding.