Form
A themeB C major choraleA′ theme, twice as fastCoda C minor
Bars 1–4 in C minor
Sections
A (1–24): the theme
Bars 1–8 cadence in G minor, and bars 9–12 turn through D♭ major, the Neapolitan ♭II, back to V⁷ and i. From bar 17 the roots fall by fifths, and bar 20 lands on VI in a deceptive cadence. In bar 24 Chopin's thirds slide down over a held C as vii°/V falls to iv.
B (25–48): the chorale
Chopin holds a low C under bars 29 and 37, and from bar 33 his bass falls F, E, E♭, D. That E major, III, does not resolve to A minor, and from bar 39 the right hand's octaves run over block chords.
A′ (49–73): the theme, twice as fast
The theme returns in C minor at twice the speed, following the harmony of bars 1–23, with iiø⁷ (D natural) in place of ♭II at bar 69.
Coda (74–77): C minor
The return stays in C minor and closes ♭II, V⁷♭9, V⁷, i across bars 72–74, and every chord after that is i, the last with E♭ on top.
Study edition
Partial analysis: opening bars and a short note on each section. The full breakdown of every section is in the study edition of Nocturne in C minor.
Where it sits among the other twenty is in the nocturnes ranked by difficulty, the method for learning it from these chords is in how to memorize a Chopin nocturne, harmony first, and the left-hand pattern under it is measured in Chopin’s left-hand patterns, ranked by stretch.