Overview
Introduction
As the first and last pieces in this set are in the same key (F minor), and the set bears some resemblance to a 4-movement sonata, these Impromptus have been accused of being a sonata in disguise, notably by Robert Schumann and Alfred Einstein, who claim that Schubert called them Impromptus, and allowed them to be individually published to enhance their sales potential.
No. 1 in F minor
This Impromptu is written in rondo form, A1–B1–A2–B2–A3. The returning A section appears always in the tonic, F minor; the first B section, B1 is in A-flat major, the relative major, whereas B2 is in the tonic. This structure can also be interpreted as a sonata form without a development section, supporting the view of the four Impromptus as movements of a single sonata. The B episodes contain a passage invoking a unique pianistic effect: the left hand presents short melodic fragments in form of antecedent and consequent, steadily alternating between the upper (antecedent, creating a crossing of the hands) and lower (consequent) registers of the instrument; the right hand accompanies with an even flow of semiquaver arpeggios in the middle register; the sustain pedal further enriches the sonority, and the dynamics are mostly pianissimo, as often in Schubert's music.
No. 2 in A-flat major
This Impromptu is written in the standard minuet form. Its main section features a melody with chordal accompaniment. The opening bars of the melody are highly reminiscent of a similar theme from the opening of Beethoven's Piano Sonata in A-flat, Opus 26. Alfred Einstein has mentioned another similar theme by Beethoven – in the third movement of the Piano Trio, Op. 70, No. 2. The middle section of the Impromptu, marked Trio as standard in minuets, is contrasted in character with the main section. It is written in D-flat major, and features continuous triplet motion. The second part of the Trio moves to D-flat minor (written in the same key signature but with accidentals added), then climaxes on A major (written without a key signature), fortissimo, and finally calms down and repeats the major-mode first phrase.
No. 3 in B-flat major
This Impromptu in B-flat major is a theme with variations. The main theme resembles a theme from the incidental music that Schubert composed for the play Rosamunde, which also appears in the second movement of his 13th string quartet. The variations follow the classic pattern utilized and developed by Beethoven – elements include increasing subdivision and ornamentation, and a modulation prior to a return to the tonic for the final full variation – see the Arietta of Beethoven's Op. 111, and most prominently, the Diabelli Variations. Like the variations movement in the Trout Quintet, this modulation is achieved by following a tonic-minor variation with one in the flat submediant, following which a brief free passage modulates back to the tonic.
No. 4 in F minor
This Impromptu contains interesting hemiola effects (where two bars of three beats seem to become three bars of two beats), brilliant passagework as well as cross modulations that take this piece to keys not traditionally associated with F minor, such as A-flat minor (for instance, in bar 111), C-flat major (as in bar 142), and A major (bar 165). It is written roughly in Rondo form and contains a coda that further heightens the drama in this already intense piece. The work is the most technically demanding of the Impromptus, employing a wide variety of keyboard writing, including scale runs (at times in unison), arpeggios, broken chords, quick passages in thirds, and trills. Extreme harmonic and rhythmic effects, combined with demonically charming melodies, make this a dazzling and fascinating display of keyboard facility.
