Kuhn and Feyerabend formulated the problem. Dilworth provides the solution. In this highly original and insightful book, Craig Dilworth answers all the questions raised by the incommensurability thesis. Logical empiricism cannot account for theory conflict. Popperianism cannot account for how one theory is a progression beyond another. Dilworths Perspectivist conception of science does both. While remaining within the bounds of classical philosophy of science, Dilworth does away with the logicism of his competitors. On the Perspectivist view theory conflict is not contradiction, and theory superiority does not consist in deductive subsumption or set-theoretic inclusion. Here the relation between theories is analogous to the application of individual concepts, and the question of theory superiority becomes one of relative applicability. In this way Dilworth succeeds in providing a conception of science in which scientific progress is based on both rational and empirical considerations.