Empirical adequacy and ramsification

Structural realism has been proposed as an epistemological position interpolating between realism and sceptical anti-realism about scientific theories. The structural realist who accepts a scientific theory ⊖ thinks that ⊖ is empirically correct, and furthermore is a realist about the 'structural content' of ⊖. But what exactly is 'structural content'? One proposal is that the 'structural content' of a scientific theory may be associated with its Ramsey sentence ℜ(⊖). However, Demopoulos and Friedman have argued, using ideas drawn from Newman's earlier criticism of Russell's structuralism, that this move fails to achieve an interesting intermediate position between realism and anti-realism. Rather, ℜ(⊖) adds little content beyond the instrumentalistically acceptable claim that the theory ⊖ is empirically adequate. Here, I formulate carefully the crucial claim of Demopoulos and Friedman, and show that the Ramsey sentence ℜ(⊖) is true just in case ⊖ possesses a full model which is empirically correct and satisfies a certain cardinality condition on its theoretical domain. This suggests that structural realism is not a position significantly different from the anti-realism it attempts to distinguish itself from. © British Society for the Philosophy of Science 2004