For example, a typical realist about length measurement would argue that the empirical regularities displayed by individual objects’ lengths when they are ordered and concatenated are best explained by assuming that length is an objective property that has an extensive structure (Swoyer 1987: 271–4). That is, relations among lengths such as “longer than” and “sum of” exist independently of whether any objects happen to be ordered and concatenated by humans, and indeed independently of whether ob