Two strategies are prominent in histories of nineteenth-century music: intertextuality and individuation. The history of nineteenth-century music is a history of works, composers and performers; traditions, media and styles; and institutions, ideas and responses. In a bold generalisation about changing historical phases in the theory of art, Carl Dahlhaus allowed the nineteenth century to embrace two developments. The first is centred on the biographies of individual composers. The second is based on the structure of self-contained works. The present-day subject inclines to a reductionist view of the past, allowing an analytical quest for common principles to subordinate constitutive diversity to an identity principle. At almost every stage, a history of music engages in rationalisations. There are two rationalisations of history, one is based on geography and the other on temporality. The first invokes the notion of centres and peripheries. The second rationalisation is the periodisation of history.