The opening movement of Mozart’s Sonata No. 2, K. 280, is an Allegro assai in F major and three-quarter time. Firm chords and short, accented phrases alternate with running notes and lighter broken-chord figures. The music repeatedly changes which hand supplies the motion: an upper run may be answered by an active bass, while a held melody note stands over moving accompaniment. Both large sections carry repeat signs in this edition.

Opening theme: A rolled upper chord introduces a short phrase supported by widely spaced bass notes. Repeated left-hand chords then create a steady pulse under the melody. The upper voice answers with accented notes and a descending run; the left hand follows with its own quick figure. Brief offbeat chords and rests interrupt the flow. Triplets bring a different subdivision of the beat, first in broken patterns and then in longer lines that move through changing harmonies.

Secondary theme and closing passage: The lower hand gives a short, strongly accented introduction before the right hand enters with a lighter stream of notes. The hands alternate between running figures and simpler chordal support. Later phrases become more detached and chromatic, with quiet replies following stronger accents. The closing material begins with a rising left-hand figure under a held upper note. This exchange returns several times, joined by trills and broken-chord accompaniment, before the first repeat.

Middle section: The new section shifts the active line into the bass beneath sparse upper chords. Short dotted figures and overlapping sustained notes follow. Upper triplet runs then alternate with broad chords and accented low notes. These quick changes of texture make the middle passage distinct from the more continuous accompaniment heard earlier. A brief slowing prepares the return of the opening theme at the original tempo.

Return and ending: The principal ideas return with changes of register and harmony. The secondary theme again contrasts a busy upper line with a brief bass response. Toward the end, longer runs pass between the hands and lead back to the rising-bass closing gesture. The final phrases combine short ornaments, a moving accompaniment, and a firm chordal cadence before the second repeat.

Interesting fact: The score places a small slowing indication immediately before the main theme returns, then explicitly restores the original tempo at the theme’s entrance.