Abstract

When discrepancies are discovered between outcomes of different measuring instruments two sorts of explanation are open to scientists. Either (i) some of the outcomes are inaccurate or (ii) the instruments measure different quantities. Here I argue that, due to the possibility of systematic error, the choice between (i) and (ii) is in principle underdetermined by the evidence. This poses a problem for philosophical views that attempt to analyze ‘basic’ measurement concepts like quantity and scale independently of ‘applied’ concepts like accuracy and error. I show that such analysis in untenable in light of scientific practice, and propose an alternative, model-based account of measurement that acknowledges the co-dependence between foundations and application. This account dissolves the problem of quantity individuation, and provides new insights into the role measurement error plays in maintaining the unity of quantity concepts.