Pierre Duhem’s (1861–1916) thesis of underdetermination of theory by data, the claim that empirical evidence alone is not adequate for providing justification for any given scientific theory, has played an important role in building up a case both for conceptual relativism (§4.2) and for constructionism and relativism about science (§4.4.2 and §4.4.3). According to the underdetermination thesis, incompatible theories can be consistent with available evidence. Relativism threatens whenever conflicting theories or views appear to have equal claim to truth or justification. The relativistically inclined use underdetermination to claim that evidence could be brought to justify opposing explanations and justification. The underdetermination thesis is also used to highlight the absence of neutral starting points for our beliefs. Choices between incompatible but equally well-supported rival theories, it is argued, are often made based on interests and local preferences rather than neutral universal grounds.