Mozart’s Sonata No. 3, K. 281, opens with an Allegro in B-flat major and two-quarter time. Its compact phrases combine trills, quick turns of direction, and contrasting touches. A delicate opening idea gives way to stronger chords and rapid runs, while the accompaniment changes between spare bass notes, repeated chords, and continuous broken patterns. The first large section repeats before an extended middle passage and the return of the main themes.

Opening theme: A trill introduces a soft upper line over widely spaced lower chords. Triplet figures flow into a brief accented response, followed by another quiet phrase in a lower register. Longer runs then rise above repeated left-hand chords. The upper line repeatedly changes from smooth motion to detached notes, and the bass interrupts with short accented replies. A descending figure passes into the left hand before the contrasting theme enters.

Secondary theme and closing passage: Repeated upper notes introduce a lighter theme over broken-chord accompaniment. Dotted figures and small ornaments decorate the melody. Rapid lines then alternate between the hands, with one hand sustaining or resting while the other moves. A more continuous lower pattern supports a longer melodic phrase, followed by shorter chordal exchanges. The accompaniment remains active as the music reaches the first repeat.

Middle section: The new passage begins softly, with an ornamented upper melody over a smooth, close-spaced lower pattern. Chromatic notes give the line a changing harmonic color. Fragments of the opening material return, and rising and falling figures pass between the hands. Later, a more sustained upper phrase appears over continuous lower notes. Offbeat replies, running triplets, and a rising chromatic figure lead back to the opening theme.

Return and ending: The main theme returns with its original contrast of delicate ornament and stronger response. The secondary idea reappears with changes of harmony and register, followed by another exchange of quick lines between the hands. A brief slowing precedes the closing passage. The final phrases combine accented upper chords with a moving lower accompaniment before a firm, short cadence.

Interesting fact: A footnote at the opening gives two possible endings for the first trill, distinguishing the editor’s preferred reading from an easier alternative.