Analysing a piece: Bach's C major Prelude
Music theory · Musical form · Level 5 · 20 min
Analysis isn't about sticking on labels: it's understanding how a piece works, so you can play and memorise it better. Here is a seven-step method, followed by a complete analysis of a famous piece.
The method
- Overview: key, metre, tempo, length, character, genre, period.
- Form: find the cadences, repeats, returning themes. Divide into sections.
- Harmony: label the chords (at least at cadences), find modulations and pedal points.
- Melody and motifs: where the material comes from, how it's developed.
- Texture and rhythm: accompanied melody, counterpoint, chords; recurring rhythmic patterns.
- Expression: dynamics, articulation, climaxes.
- Consequences for performance: where to breathe, where to peak, what to bring out.
The Prelude in C major BWV 846 (Bach, 1722)
The first piece of the Well-Tempered Clavier. Overview: C major, 4/4, 35 bars, a single arpeggio pattern repeated in every bar. So the whole piece is a chord progression: one chord per bar, broken in the same shape. Here is the first bar as you hear it:
M:4/4
L:1/16
%%staves {RH LH}
V:RH clef=treble
V:LH clef=bass
K:C
[V:RH] z2 Gc eGce z2 Gc eGce |
[V:LH] C E7 C E7 |
And the chordal reduction of the first four bars:
M:4/4
L:1/4
%%staves {RH LH}
V:RH clef=treble
V:LH clef=bass
K:C
[V:RH] "C"[EGce]4 | "Dm7/C"[DAdf]4 | "G7/B"[DGdf]4 | "C"[EGce]4 |]
[V:LH] "_I"C4 | "_ii4/2"C4 | "_V6/5"B,4 | "_I"C4 |]
The plan
| Bars | What happens |
|---|---|
| 1-4 | Establishing the tonic: I – ii4/2 – V6/5 – I, over an almost motionless bass (C – C – B – C). |
| 5-11 | Modulation to G major (the dominant): Am/C, D7/C (V7 of G), G/B, Cmaj7/B, Am7, D7/A, and a cadence in G in bar 11. |
| 12-19 | Back toward C over a descending bass and diminished seventh chords, reaching the C chord (bar 19). |
| 20-23 | Chromatic chords (a C7 pulling toward F, then diminished sevenths) preparing the big moment. |
| 24-31 | Dominant pedal: the low G is held for eight bars under increasingly tense chords. The peak of tension. |
| 32-35 | Tonic pedal: C in the bass, C7 → F/C → G7/C → C. The calm conclusion, with a final block chord. |
Consequences for playing
- Play the piece first as block chords, one bar at a time: you'll memorise it through the harmony rather than the fingers.
- Spot the common tones between neighbouring bars: they reveal the voice leading, which is flawless.
- Build the dynamics toward the dominant pedal (bars 24-31), then release.
- Pedal: either none (Baroque purity, finger legato) or an exact change at each bar, never mid-bar.
Your turn: do the same analysis on a piece from Schumann's Album for the Young Op. 68, for example “Melody” (No. 1) or “The Happy Farmer” (No. 10): look for phrases, cadences and form (often ABA).
Analysis isn't an end in itself: if a label doesn't help you hear or play better, move on. Two analysts may label the same chord differently; what matters is understanding the musical motion.