Schubert's fourth impromptu is in ternary form: a scherzo, a trio in C♯ minor, and the scherzo again, followed by a short coda. On the surface it is all fluency, a cascade of sixteenths that hardly stops. Underneath, the piece is unusually patient with its home key, and unusually even-handed with its climaxes.
The opening right hand looks like accompaniment, a turning figure of sixteenths falling through the chord, but nothing sits above it: the run is the melody, over harmony that moves only about once a bar. The tune then travels, slipping into a tenor voice beneath the run in the major section, and into the right hand's upper voice, in long notes, in the trio.
The key signature is A♭ major's, but the opening paragraph is in A♭ minor, and the major arrives only as a change of mode on the same keynote. The scherzo's peak comes at m. 64, on the arrival in D♭ major: the highest note in the piece, marked ff. Even so, the home key never receives a perfect authentic cadence; those belong to the trio alone.
The trio is in C♯ minor, which sounds as D♭ minor written in sharps, and the sixteenths give way to steady repeated chords under a low melody. Its own climax, at mm. 127 and 135, is one of breadth rather than height: the bass rises a semitone above the dominant and sinks back while the hands spread across the widest span in the piece. With its repeats, the trio is heard for a little longer than the scherzo on either side of it.
A single held chord leads back to the scherzo, which returns note for note with every dynamic marking stronger. In the coda the chord that once led into the trio comes back and leads nowhere; a bare octave, neither major nor minor, gives way to the final A♭ major chord.
| Section | Bars | Tonal area |
|---|---|---|
| Scherzo | 1–106 | A♭ minor and A♭ major; C♭ major turning to B minor; D♭ major |
| Trio | 107–164, both parts repeated | C♯ minor; G♯ minor; C♯ major |
| Scherzo return | 165–268 | A six-bar retransition on the dominant of A♭, then the scherzo as mm. 1–98 |
| Coda | 269–280 | A♭ major |
Bar numbers follow the Breitkopf & Härtel edition (1888); the first and second endings of the trio's first part are not numbered.
The impromptu moves through few keys, and each lies a simple step from A♭: its relative major, its subdominant, and the subdominant again in the minor. What makes the journeys striking is the notation. Several keys are written in sharps although they sound as flat keys, so the music looks far from home while staying close to it, and the trio's one modulation arrives, under another name, at the key the piece began in.
From A♭ minor to C♭ major, its relative major, which darkens into its own minor and is written as B minor before the music turns home. After the change to A♭ major, a sequence reaches D♭ major, the subdominant and the most lightly confirmed key in the piece, which is soon drawn back into A♭.
C♯ minor, the minor subdominant written in sharps, and the only change of key signature in the piece. The first part closes in G♯ minor, the home key spelled in sharps. The opening music then returns in C♯ major, turns briefly aside, and closes in C♯ minor.
The scherzo's keys recur unchanged and in the same order. In the coda the chord that once led into the trio returns, but no new key follows: the piece stays in A♭ and ends in the major.
The study guide's Integrated Analysis traces how each change of key is made, and its Appendix B indexes every one.
Imperfect authentic cadences throughout, several of them repeated closing gestures in the major. A half cadence ends the minor opening on its dominant, and a deceptive cadence turns a hinted new key back on itself. The arrival in D♭ is confirmed only lightly.
The only perfect authentic cadences in the piece: at the close of the first part, in G♯ minor, and at the close of a′, in C♯ minor. Between them, half cadences over the dominant and deceptive cadences that sidestep the tonic.
The scherzo's cadences recur in the same order and keys, the first of them now completing the retransition. The last cadence of the piece, in A♭ major, is again imperfect. Every cadence in the piece lands on a downbeat.
The turn from A♭ minor to A♭ major, a change of mode rather than of key. The respelled chords that carry the music into the trio and back out of it. In the coda, the chord that once opened the trio, left unresolved, and the bare octave that follows.
Every cadence's location, type and approach is listed in Appendix A of the study guide, Confirmed Cadence Locations.
Appendix B indexes every change of key, with the means of each change.
The scherzo varies its continuous sixteenths by register and by an added voice rather than by thicker chords, and holds the piece's highest note and every ff; the trio halves the motion to repeated eighths and holds the lowest note, the widest span and the heaviest chords. The return copies the scherzo's notes but not its markings, so its last appearance is also its most forceful.
Analysis and study materials published as they appear.