What, then, are we to make of Beethoven's title: Sonata quasi una fantasia? What might have prompted it, and what are the implications of its generic cross-fertilisation? Recent theories of genre suggest a number of avenues for the exploration of these questions. Following the tenets of Russian formalist critics, studies could be made of the defining structural patterns associated with the classical sonata and eighteenth-century improvised fantasy, and of their relationship to one another in the fantasy-sonatas. Central to the formalist view of genres is the concept of a ‘dominant’, a defining element that categorises a genre and determines the function of other elements within it. Since Beethoven called these pieces Sonata quasi una fantasia rather than Fantasia quasi una sonata, the dominant generic strand seems self-evident. But the crucial ways in which sonata elements determine the functions of fantasy elements are not so straightforward.

Alternatively, the historical dimension of genre might be prioritised. Taking a lead from H. R. Jauss, a genre could be viewed as a historical ‘family’ of works.