The logical empiricists knew that scientific theories sometimes arise out of the attempt to reconcile or unify two existing theories. They also thought that, at best, old theories would be retained as approximations to their successors. Kuhn lost both insights when he rejected the logical empiricists' formal approach in favor of an exclusively historical and psychological one. But when Putnam tried to restore such ideas he failed to provide them with the historical support they require. An account of revolutionary unifications (...) is defended as reconciling Putnam's realist ideas about methodology with Kuhn's historical approach. (shrink)