Underdetermination

Underdetermination is the condition in which available evidence is compatible with multiple competing theories. It limits how decisively evidence alone can select among explanations.

Duhem–Quine thesis: The view that hypotheses are tested together with auxiliary assumptions, so evidence rarely tests one claim in isolation. It explains how failed predictions can leave multiple parts of a theory open to revision.
Pyrrhonism: An ancient Greek skeptical tradition that recommends suspending judgment when arguments appear balanced. Its practice of withholding assent anticipates the challenge posed by equally evidence-compatible theories.
Theory choice: The practice of selecting among scientific theories using evidence and methodological considerations. It concerns how scientists act when underdetermination prevents evidence from settling every choice.
Scientific objectivity: The ideal that scientific claims and methods are not determined by individual preferences or interests. Underdetermination raises questions about whether methodological choices can remain objective when evidence permits alternatives.
Auxiliary hypothesis: An assumption used alongside a central hypothesis to derive predictions or interpret evidence. Changing these assumptions can preserve a theory when observations conflict with its predictions.
Pierre Duhem: A French physicist and philosopher of science who argued that experiments test theoretical systems, not isolated hypotheses. His account of physical testing became a source of modern arguments about underdetermination.
Inference to the best explanation: An inference that favors a hypothesis because it provides the strongest explanation of the available evidence. Explanatory virtues can rank theories that remain equally compatible with observations.
Theory-ladenness of observation: The idea that observation and its interpretation can depend partly on background concepts and expectations. If observations are interpreted through theories, they may not provide a neutral tie-breaker between them.
Confirmation holism: The view that evidence bears on interconnected bodies of belief rather than isolated hypotheses. It shows why the same observation can support or challenge different parts of competing theories.
W. V. O. Quine: An American philosopher who defended confirmation holism and emphasized the revisability of scientific belief. His work extended Duhem's point into a broad account of how evidence bears on theories.

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