Bach: Prelude and Fugue No.17 in A♭ major, BWV 862 Analysis



Bach Prelude and Fugue No.17 in Ab Major BWV 862 Analysis 1


Bars 1-18: Period I. Ending with a Perfect Cadence in the key of the Dominant E flat.

Bars 18-44: Period II. Beginning on the Dominant, and ending with a Perfect Cadence in the key of the Tonic, A flat.

Bars 35-44: Coda. Further confirmation of the Original key.


This Prelude is constructed chiefly upon the figure used in the Treble of Bar 1.

Period I has a subdivision at Bar 9.

At the beginning of Period II the Theme is started in the key of the Dominant.

The Coda is constructed upon Free Imitation of the Theme in a descending Sequence.



Bach Prelude and Fugue No.17 in Ab Major BWV 862 Analysis 2



Bars 1-2: Subject in Tenor [A flat major].
Bars 2-3: Tonal Answer in Bass, with free Counter-subject in Tenor [E flat major].
Bars 3-5: Codetta.
Bars 5-6: Subject in Treble. Part of Counter-subject in Bass [A flat major].
Bars 6-7: Answer in Alto. Counter-subject absent [E flat major].
Bars 7-10: Episode I, modulating from E flat to A flat.
Bars 10-11: Subject in Tenor. Counter-subject (varied) in Bass.


Bars 11-13: Episode II, modulating from A flat to F minor.
Bars 13-14: Subject in Alto. Counter-subject (varied) in Tenor [F minor].
Bars 14-17: Episode III, modulating after close in F minor, to B flat minor.
Bars 17-18: Subject in Tenor. Counter-subject absent [B flat minor].
Bars 18-19: Answer in Alto [B flat minor].
Bars 19-21: Episode IV, modulating from B flat minor to A flat major.
Bars 21-22: Fragment of Subject in Alto and of Answer in Treble.
Bars 23-24: Answer in Alto (altered at 5th note). Counter-subject in Tenor [A flat major].
Bars 24-25: Subject in Treble. Counter-subject in Tenor [E flat major].
Bars 24-25: Subject (varied) in Alto and developed into a sequence of of suspended 9ths [A flat major].
Bars 25-27: Episode V, modulating sequentially from D flat to A flat.
Bars 27-28: Subject in Bass [A flat Major].
Bars 28-29: Answer in Tenor [C minor].
Bars 29-30: Answer in Alto. Free version of Counter-subject in Tenor [A flat major].
Bars 30-31: Answer in Treble [D flat major].


Bars 31-35: Coda [A flat major].
Bars 33-34: Subject in Treble [A flat major].
Bars 35: Counter-subject (reminiscence of) in Alto [A flat major].


Exposition: Bars 1-7.
Counter-exposition: None.
Episodes: Five.
Stretti: None.
Pedal: None.
Coda: Bars 31, 35.


  1. This Fugue has a “tonal” Answer, and would be called a “tonal” Fugue. The alternation in the Answer, for the sake of tonality, is made from the second note to the third.
  2. The free Counter-subject is occasionally dispensed with and a new melody substituted for it, thus imparting additional interest and variety to the Fugue.
  3. The following is a description of the Episodes, which for the most part are founded upon the free Counter-subject , but other figures of melody are occasionally added:
    1. Episode I. Built upon the Counter-subject in the Alto and imitated by the Bass in the octave, a contrasted counterpoint being given to the Treble.
    2. Episode II. Free imitation of the Subject in the Bass. Suspensions in the Tenor, with ornamental counterpoint in the Treble.
    3. Episode III, IV. These retain the melodic figures of the Episode II, but transferred to different voices (observe, Episode III is distant one bar only from Episode II).
    4. Episode V. Suspended figures in the two upper parts with a running Tenor founded on the Counter-subject.
  4. The entries in Bars 21, 27-30 do not constitute real Stretti, because they do not overlap each other.