Incommensurability

Incommensurability is the difficulty of directly comparing frameworks that organize concepts, evidence, and standards differently. The term is especially associated with debates about scientific theories and translation across languages.

Paradigm shift: A major change in the shared assumptions and practices that organize scientific research. A shift can make earlier and later theories use different standards and categories.
Thomas Kuhn: An American historian and philosopher of science known for his account of scientific revolutions. Kuhn made incommensurability central to explaining conflicts between scientific paradigms.
Commensurability: The possibility of comparing quantities, theories, or frameworks using shared standards. It names the condition that incommensurability denies or limits.
Copernican Revolution: The historical shift from Earth-centered astronomy toward a Sun-centered account of the planetary system. It illustrates how changing astronomical frameworks altered explanations and standards of adequacy.
Theory-ladenness: The dependence of observation, interpretation, or measurement on theoretical assumptions. Different frameworks can classify the same evidence differently because observation is theory-laden.
The Structure of Scientific Revolutions: Thomas Kuhn’s 1962 book arguing that scientific development includes paradigm shifts. The book introduced the influential account of paradigm change behind the debate.
Scientific realism: The view that successful scientific theories describe a reality existing independently of thought. Realist accounts ask how theories with changing concepts can still concern the same world.
Phlogiston theory: An eighteenth-century theory that explained combustion through the release of a substance called phlogiston. Its replacement by oxygen chemistry raised questions about continuity between rival explanations.
Conceptual scheme: An organized set of concepts through which a person or community interprets experience. Incommensurability concerns the comparison of such organizing frameworks.
Paul Feyerabend: An Austrian-born philosopher of science who challenged universal rules for scientific method. Feyerabend developed a stronger account of conceptual change and theory comparison.

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