The Necessity Argument Against Naturalism: Deduction, Necessity, and the Incoherence of Contingency-Only Metaphysics

This monograph argues that metaphysical naturalism cannot account for deductive reasoning. Deduction presupposes necessary truth: valid inference is necessarily truth-preserving, not merely reliable. This necessity is ontological, constraining what can be the case, not merely what can be thought. Metaphysical naturalism, consistently articulated, holds that all facts supervene on contingent physical facts and denies non-contingent features of reality. The two commitments are incompatible. Naturalist attempts to reintroduce necessity through laws of nature, mathematical abstraction, counterfactuals, dispositions, or brute necessity either fail to supply genuine ontological necessity or abandon naturalism's core commitments. The denial of necessary truth is self-defeating: any such denial must be offered as necessary, in which case it refutes itself, or as contingent, in which case it fails to exclude necessary truths. The argument is logically prior to related critiques such as the Evolutionary Argument Against Naturalism and the Argument from Reason, which presuppose the modal framework this argument places in question.