 An instance of the divide et impera strategy is structural realism. This view has been associated with John Worrall (1989), who revived the relationist account of theory-change that emerged in the beginning of the twentieth century. In opposition to scientific realism, structural realism restricts the cognitive content of scientific theories to their mathematical structure together with their empirical consequences. But, in opposition to instrumentalism, structural realism suggests that the mathematical structure of a theory represents the structure of the world (real relations between things). Against PI, structural realism contends that there is continuity in theory-change, but this continuity is (again) at the level of mathematical structure. Hence, the ‘carried over’ mathematical structure of the theory correctly represents the structure of the world and this best explains the predictive success of a  theory.[8]