Form

Binary
A A'

Introductory Theme (E flat major)

Theme (C minor)

Motive

Notes

After the first two movements of bright moods and animated energies, Mozart settles down into a longing adagio which darkens the palette through ample use of minor keys. The trio of the previous movement emphasized the two outer voices, violin and cello. The adagio extends this texture to the point of a true operatic duet, a melancholy longing offered by one voice, compassionately heard and echoed by the other. A lovely moment of repose, the quartet's center of gavity, a shadowed dream compared to the bright daylight of the other movements.

The form of the movement is essentially binary. The first pass, or verse, begins in E-flat major (the subdominant key of the quartet's home key of B-flat-major) and moves through C-minor to reach its dominant key of B-flat-major. The second time around, the harmony uses F-minor so that it eventually returns to E-flat major, rhyming the first verse transposed into the tonic key. The second refrain is elongated slightly, giving a touch of greater maturity to the restatement in the "proper" key.

The first theme is merely introductory in nature. It establishes the key, but no strong continuity of motion. Indeed, it is interrupted. The long rising arpeggio is the lynchpin which, upon its second appearance, shifts into the minor and gives way, somewhat surprisingly, to the first substantial theme in C-minor. This arpeggio again transports the movement into the minor (F-minor) during the second refrain. At it appears one more time: in the last few measures. Once again, it signals a pending transition. This time, it spells the end as the momentum resigns into a very soft and light finish on the tonic.