The No-Miracles Argument for Realism

Core Idea

The 'no miracles' argument provides realism's strongest defense: if theories were not approximately true, their predictive success would be miraculous. Since we do not believe in miracles, successful theories must be (mostly) true about the world. This abductive argument remains the most influential justification for scientific realism.

Common Misconceptions

Thinking the no-miracles argument is deductively valid (it is abductive, relying on inference to best explanation). Assuming it rules out all anti-realist alternatives. Ignoring that structural realism admits underdetermination while preserving some realist commitments.

Explainer

From your study of scientific realism, you know the core claim: our best theories are approximately true, and the theoretical entities they posit (electrons, DNA, curved spacetime) really exist. What justifies this? The scientific realist's strongest answer is the no-miracles argument, developed by Hilary Putnam: if our theories were not approximately true, their remarkable predictive success would be an unexplained miracle. Since we reject miracles as explanations, we should infer approximate truth.

The argument's logical structure is inference to the best explanation (IBE), also called abduction. Premise 1: our best scientific theories make precise, novel predictions that succeed far outside the conditions under which they were formulated. Quantum electrodynamics predicts the electron's magnetic moment to eleven decimal places. General relativity predicted the bending of starlight around the sun before it was observed. These are not mere empirical fits; they are striking successes in new domains. Premise 2: the best explanation of this success is that the theories are approximately true descriptions of the world, including its unobservable parts. If electrons, quarks, and spacetime curvature approximately behave as described, the theories' success is expected. If the theories were just useful fictions with no connection to reality, the success would require an astronomical coincidence. Conclusion: the theories are approximately true.

The argument's vulnerability, as you've seen in underdetermination, is that empirical equivalents are always possible — theories with the same observational consequences but different theoretical ontologies. The anti-realist can say: success confirms empirical adequacy, not truth. Bas van Fraassen's constructive empiricism accepts that theories should be empirically adequate (true about observables) while remaining agnostic about unobservables. The no-miracles argument, the anti-realist charges, implicitly assumes that IBE is a reliable guide to truth for unobservables — but this is exactly what's in question.

The most devastating challenge is the pessimistic meta-induction: the history of science shows that predictively successful theories have repeatedly turned out to be false. Caloric theory successfully predicted heat flow; phlogiston theory organized combustion chemistry; Newtonian mechanics predicted planetary orbits to astonishing precision. All were later shown to be approximately false in their core theoretical claims. By induction over this history, our current theories — however successful — are probably false too. Realists respond by arguing that theory change is more conservative than the pessimist claims: successful theories leave a structural residue in their successors. Fresnel's optical ether was abandoned, but the mathematical equations describing light waves were preserved in Maxwell's electromagnetism. This observation motivates structural realism: what persists across theory change and what successful theories likely get right is not the nature of the entities, but the mathematical structure of the relationships between them — a realism that concedes much to the anti-realist while preserving the no-miracles intuition about structural truth.