Thematic structure in the classical style is incredibly diverse and interesting, and has been studied by music theorists for more than two centuries. In this collection of resources, we are concentrating on thematic structure in the Classical style, as opposed to the Baroque or Romantic eras, for two primary reasons. First, it has been most discussed and is best understood. Because a wealth of writing has dealt with classical cadence, motivic structure, phrase organization, and so on, we are well positioned to approach the subject fairly systematically. Of course, our systematic approach should not be taken to mean that we are able to explain everything. Even among music theorists that have developed robust theories of classical form (Hugo Riemann, for example), flexible analysis is still important. Second, understanding thematic structure in the classical style will give us a way into the most important instrumental forms of the time: not just sonata form, but minuet and rondo as well. Those forms have an amazing longevity, and it will benefit us to approach them as they are emerging historically.
Our descriptions of classical thematic structure are borrowed primarily from William Caplin, whose treatise Classical Form, borrows ideas from Arnold Schoenberg and Erwin Ratz. Caplin’s explanations of the various types of theme found in the classical style is systematic and practical while allowing for flexible application.
Many music theorists have studied how themes are expanded and contracted. The two short resources here, on external and internal expansions, borrow from William Rothstein’s Phrase Rhythm in Tonal Music.