Independence and the Limits of Confirmation: On the Underdetermination of External-World Hypotheses

Scientific confirmation relies on the convergence of independent sources of evidence. When multiple observers, instruments, or experiments yield the same result, the improbability of coincidence supports the conclusion that an external fact caused the agreement. This paper argues that the independence assumptions underwriting such inferences cannot be justified without presupposing the external-world framework they are meant to establish. Independence is not an observable property of data but a structural claim about data-generating processes---a claim that requires substantive background assumptions about distinct systems, causal separation, and error mechanisms. These background assumptions are justified only relative to models that already presuppose external reality. The result is not that external realism is false, nor that intersubjective agreement provides no evidence, but that the degree of confirmation is underdetermined without framework-level commitments that cannot themselves be confirmed by the same methods. This underdetermination extends to perception itself: the intervention-structured patterns of experience are compatible with multiple metaphysical embeddings. The paper concludes not with an alternative metaphysics but with the recognition that questions about the ultimate source of experience are underdetermined by any evidence expressible within experience.