Imagine blanking out, say, the ‘second theme’ of Mozart’s Piano Sonata, K. 284, first movement, exposition, an exquisite development of the opening theme, which relationship may even have been the composer’s deliberate narrative.
Then imagine, instead, blanking out bars 1-8, which we might call Mozart’s main ‘idea’ here. The latter recomposition may seem more radical, but in fact probably makes vastly more overall sense of what we call the exposition.
The former is embarrassing—anyone schooled in Western art music can hear how gauche and unviable it is. Yet mine, though also a pointless mutilation, and an equally lamentable model for students of Western art music, would nevertheless work quite well as it were ‘grammatically,’ don’t you think?
Start the sonata at bar 9, and there’s no immediate problem; it would take a while until even as a highly expert listener you smelled a rat, and if you insist on recomposition, then at least mine has the virtue of demonstrating other than in words that to understand the ‘second theme’ as some kind of insertion, or ornamental, is what I believe our scientific colleagues call: an error.
To convey the harmonic-contrapuntal function of the K. 284i, ‘second theme,’ I recommend Salzer’s 1962 (in English) distinction between prolongation ‘of’ and prolongation ‘to,’ for which there is an elegant graphic notation, forward- and backward-pointing arrows.
Professor of Music Theory
Eastman School of Music