Allegro ma non troppo, A minor, 6/8 time

It is in sonata form. The movement opens forte with the tonic chord of A minor, then crescendos from piano towards a dominant ninth chord. This antecedent phrase consists of three measures, followed by a two-measure consequent phrase with an arpeggiated dominant ninth chord, after which the theme is presented again. The unstable character of the theme is emphasized not only by the dynamic range but also by the irregular phrase structure of 3 measures + 2 measures. After the re-presentation of the theme, it does not remain in A minor, but modulates several times to remote keys already within the exposition.

After being separated by a general pause, the second theme is presented in F major (m. 28). Choosing a major key a major third below the tonic, rather than the relative major, for the second theme was by no means a violation of rules for Schubert (cf. for example, the Unfinished Symphony, D 759). The two themes contrast in terms of dynamics and character.

At the end of the exposition, modulations are layered through the repetition of motives, thereby introducing the development section (m. 73). The development section is also divided into two parts by a general pause, characterized by a contrast between a forceful and energetic first half, beginning in sharp keys and played forte, and a lyrical and subdued second half, beginning in flat keys and played piano.

When the development section closes with a half cadence in D minor, after a general pause, the first theme returns in D minor. Recapitulation in the subdominant key is famously seen in the first movement of Mozart's Piano Sonata in C major, K. 545, but Schubert had already employed this technique in his Piano Sonatas No. 2, D 279, and No. 3, D 459. Utilizing the tonal relationship of the exposition, which progressed to a key a fifth higher, the second theme returns in A major, and the opening motive appears as a coda, bringing the movement to a close.