 Realism about measurement should not be confused with realism about entities (e.g., electrons). Nor does realism about measurement necessarily entail realism about properties (e.g., temperature), since one could in principle accept only the reality of relations (e.g., ratios among quantities) without embracing the reality of underlying properties. Nonetheless, most philosophers who have defended realism about measurement have done so by arguing for some form of realism about properties (Byerly and Lazara 1973; Swoyer 1987; Mundy 1987; Trout 1998, 2000). These realists argue that at least some measurable properties exist independently of the beliefs and conventions of the humans who measure them, and that the existence and structure of these properties provides the best explanation for key features of measurement, including the usefulness of numbers in expressing measurement results and the reliability of measuring instruments.