Bars 1 to 5

The theme of the prelude is presented in the first bars:

• A descending bass line moves from the tonic to the dominant.
• A tonic arpeggio in the upper voice, with two nonharmonic tones in the first bar (in red), is repeated twice.
• The G of the arpeggio becomes a major seventh in the second bar and a ninth in the third.

The first bars:

Bars 5 to 17

A progression takes us from E flat major to G minor. Below is a harmonic analysis of the passage. We have also indicated the main motives:

Bars 17 to 26

When we reach G minor, the theme reappears, followed by a development that takes us to C minor and finally F minor:

Bars 26 to 33

• Bars 26 to 30: a cycle of fifths brings us to the dominant of F minor (bars 29 and 30).
• Bars 31 to 33: the tonic chord is followed by a Neapolitan sixth to confirm the F minor tonality.

Bars 33 to 40

• Bars 33 to 34: the bass begins to repeat the downward movement of the first bars.
• Bars 35 to 36: a natural D in the bass begins a modulation to C minor, which is confirmed in bar 36.
• Bars 37 to 40: a cycle of fifths leads us to rest on the dominant of C minor with a minor ninth.

Bars 40 to 47

Another cycle of fifths - this time using ninth chords - ends in C minor in bar 47.

Final bars

Bach delays the end of the prelude by means of deceptive cadences and unexpected resolutions.

Complete Prelude