Closed, Closing, and Close to Closure: The Nineteenth-Century “Closing Theme” Problem as Exemplified in Mendelssohn’s Sonata Practice

There is little theoretical consensus on what constitutes a closing theme in a sonata-form exposition. William Caplin’s formal-functional theory essentially rejects the notion, while conversely it is upheld in James Hepokoski and Warren Darcy’s sonata theory. For them, a “C-theme” is defined contextually, as occurring after a decisive cadence. Yet there appear to be exceptions to this rule, more prevalent in the nineteenth century, which concern “apparent C-zones in the absence of an EEC,” or “Sc themes,” in which rhetorical factors override the lack of preceding cadential closure. This concession opens up a theoretical minefield that has until now been barely explored; nevertheless, it speaks to a genuine feature of nineteenth-century sonata practice. This article examines the use of apparently rhetorical C themes in a precedential situation in the first half of the nineteenth century, taking the sonata expositions of Felix Mendelssohn as a case study. Mendelssohn’s music highlights this issue particularly well owing to his customary avoidance of cadential closure and regular recourse to primary-theme material toward the end of an exposition. Combining form-functional and sonata-theoretical perspectives, I identify in his music a characteristic structure whereby the functions formerly reserved for a single theme are expanded to encompass what would have formed multiple themes in the late eighteenth century. Moreover, the P-based closing idea generally functions as a large-scale cadential phrase in an enormous sentence initiated by the secondary theme, thus highlighting a latent terminological ambiguity over whether the word “closing” indicates “already closed” or “in the process of closing.” I argue for the need to refine existing terminology in order to distinguish between these two meanings when applied to the nineteenth-century repertory.