String Quartet No. 15 (Schubert)

The String Quartet No. 15 in G major, D. 887, was written by Franz Schubert in June 1826. It was posthumously published in 1851, as opus 161.

The piece is in four movements, and is about 50-55 minutes long:

As the first movement's Allegro molto moderato begins alternate major and minor chords (in a characteristic dotted rhythm many forms of which will be heard throughout the quartet) and modes dizzyingly, a few bars for each at a time, and the movement becomes more stable only with the introduction of the main lyrical theme at bar fourteen. The first movement is riddled with tremolandi, which also lead into the repeat of the exposition, and contains several other new departures for the composer.

This may include the use of a motive in triplets to connect the first and second main groups of this sonata form; the second group opens, exactly as happens in the later-written String Quintet and similar to the technique in some works by Beethoven — not in the dominant key but with a quiet theme in the mediant, B-flat, with rhythm not quite the same as that of the lyrical theme that slowed matters down early on (bar fourteen, again), and with pizzicato accompaniment. There is a triplet-dominated, agitated transition and the same theme is heard, now in D, with triplet accompaniments; the triplets, not the theme, continue to the end of the exposition, and descend gradually from D down to G major for the repeat, or for the second ending and the beginning of the development, where continuity means the continued rustling of quiet strings, building for a bit by exchanging with more energetic passages, then bringing in faster versions of the dotted rhythms of the main themes. The climax of the development leads to a particularly quiet recapitulation, much varied at its opening from what we had heard originally. In the coda the opening of the quartet, both its rhythm and its major/minor exchanges, get a further chance to play themselves out.

There is a remarkably innovative harmonic passage in the first movement. Between mm. 414 and 429 Schubert prolongs G major with an equal subdivision of the octave using major 3rds. Passing seventh chords in the bass provide a smooth linear progression connecting these major thirds, the result of which is a descent in whole tones in the bass-voice cello. The following major 3rd prolongations occur: G(mm. 414-416) E-flat(mm. 417-418) B(mm. 419-420) G(mm. 421-422) E-flat(423-426). In measure 426 Schubert enharmonically reinterprets this dominant-seventh structure, resolving it as a German augmented 6th, thus proceeding bVI-V-I in mm. 427-429.

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