Waxing Rhapsodic within Tonality
My Rhapsody for Woodwinds and Piano is harmonically adventurous in places, even flirting with exoticisms such as octatonic, but the underlying harmonic motion is a conventional I-V-I progression. The details of the progression, as outlined in the graph below, are unusual and subtle.
The Rhapsody‘s introductory section (bars 1-15) sets the tonal center clearly on C, but the third is initially omitted from the tonic harmony, leaving the mode (major or minor) ambiguous and lending a misterioso quality to the section. (This introduction has a rather exotic harmonic structure in itself, but I will leave that for a future blog post. 🙂 ) The key of C Major is firmly established only with the entry of the main theme, stated by the bassoon beginning in bar 16.
The Tempo di marcia section begins in G minor, the minor dominant. But instead of progressing directly to the major form of the dominant, this G minor harmony begins a broad iv-v-V-i progression within a supertonic (ii) secondary tonality. Relative to this D minor center, the march progresses from G minor (iv) to A minor (v), building and subsiding into a Molto tranquillo section centered on A major (V), which ushers in the fugue in D minor (i).
This tonicization of D minor (ii in the overall key of C major) prepares the move to G major (V7) at bar 182 of the fugue. The return to C major (I) coincides with the joyous reprise of the main theme in bar 204.