4.5: Classical Theme Types - Compound Sentence
The compound (or 16-bar) sentence expands both the presentation and continuation phrases of a regular sentence to a length of eight bars each.
Each 2-bar basic idea is replaced by a 4-bar compound basic idea in the expanded presentation.
A “typical” continuation would have approximately four bars of continuation function followed by four bars of cadential function, but in a compound sentence, this varies greatly. The continuation is commonly shortened or expanded .
The eight bars that comprise the continuation of the main theme below are constructed from two compound basic ideas, the first beginning on tonic and moving to dominant (mm. 1-4), and the second beginning with dominant harmony and moving back to tonic (mm. 5-8).
Initially, the continuation seems as if it will end after only 4 bars, in m. 12. But the clarinet is missing at the the downbeat of m. 12, and instead begins a link to a four-bar repetition . In this repetition (mm. 13-16), the clarinet melody from mm. 9–12 is played by the piano, who cadences clearly with a PAC at the downbeat of m. 16.
COMPOUND SENTENCE: MOZART, TRIO IN E-FLAT MAJOR FOR CLARINET, VIOLA, AND PIANO, K. 498, I, MM. 1-16