Most music theorists and historians would surely agree that the style and structure of a composition are conditioned in various ways by its performance medium. Nevertheless, in dealing both with individual works and with general categories – sonata-allegro form, for example – analysts tend to focus primarily on thematic, harmonic, and (more recently) voice-leading factors with the medium regarded only as a means of realization. Analytical essays seldom consider how the structure of a sonata-allegro or other movement of a symphony, quartet, or sonata might have been shaped and, to some extent, even determined by the nature of the medium. On the other hand, historical studies of a given style – studies that may include a consideration of performance media and genres – typically discuss the music in primarily descriptive terms.

In no genre are medium and structure more inseparable than in the symphony, where the variety and grouping of instruments within the ensemble can influence virtually every facet of the compositional process. In a sense one cannot speak of the symphony as a single genre, since the makeup and character of the orchestra changed so radically from the era of mid- and late-eighteenth century ensembles to the larger orchestras of the nineteenth and twentieth centuries. Nevertheless many aspects of symphonic style that were well established in Mozart's era, often initiated by Mozart himself, continued to have profound implications for the structural character of later symphonic works.