The employment of the four themes is notable throughout this Prelude, which is of unusual length and pretension.
- Theme I: Bars 1-4.
- Theme II: Bars 5-6:
- Theme III: Bar 7.
- Theme IV: Bar 11.
Bars 1-17: Period I. Ending with a Perfect Cadence in the key of the Dominant, E flat.
Bars 17-34: Period II. Ending with a Perfect Cadence in the key of the Relative Minor, F.
Bars 34-50: Period III. Ending with a Perfect Cadence in the key of the Subdominant Major, D flat.
Bars 50-77: Period IV. Ending with a Perfect Cadence in the key of the Tonic.
The construction of the Opening material is notable. The Bass steps downwards through the notes comprising its common chords, a slight ornamentation being placed between the principal notes of the chord (Bar 1). In the third bar the same structure takes place upon the second Inversion (root + 4th + 6th). The three upper parts are made up of plain chords with the insertion of an occasional Passing Note for the sake of vigour, the whole forming a block of work (four bars in length), which as the Prelude proceeds is shifted bodily into the following attendant keys of the Tonic: (1) at Bas 17-21, into the keys of the Dominant (E flat). (2) at Bars 34-38, into the key of the Relative Minor (F). (3) at Bars 50-52 (curtailed) into the key of the Subdominant Major (D flat).
The different curves at the end of Theme II and Theme should be noted.
The lower parts of Theme II is very frequently employed, but the upper part is not again used in its entirety; on the other hand both parts of Theme II are frequently used, and in conjunction in the course of the movement.
Theme IV (which first appears in Bar 11 – upper part), seems to have had its first limb of four notes thrown immediately over, and made to give way for the figure proposed in Bar 12, to every other detail of which it is similar. It however, appears again in full force and in an ascending Sequence at Bar 44.
It is also note-worthy that all these figures are presented as early as possible in the movement.
The Periods are not capable of subdivision.
Bars 1-3: Subject in Alto [A flat major].
Bars 3-5: Tonal Answer in Treble, with Counter-subject in Alto [E flat major].
Bars 5-6: Codetta, modulating from E flat major to A flat major.
Bars 6-8: Subject in Tenor, with Counter-subject in Treble [A flat major].
Bars 8-10: Answer in Bass, with Counter-subject in Tenor [E flat major].
Bars 10-13: Episode I, modulating from E flat to A flat major.
Bars 13-15: Subject in Bass, with Counter-subject in Tenor [A flat major].
Bars 15-16: Codetta, modulating from E flat major to F minor.
Bars 16-18: Answer in Alto. Counter-subject absent [E flat major].
Bars 18-20: Subject in Tenor, with Counter-subject in Alto [A flat major].
Bars 20-22: Codetta, modulating from A flat, through D flat, and back to A flat.
Bars 22-24: Subject in Treble, with Counter-subject (first part only) in Bass [A flat major].
Bars 24-26: Subject in Alto, with Counter-subject in Treble [F minor].
Bars 26-32: Episode II, modulating from A flat, through C minor, to E flat minor.
Bars 32-34: Subject in Tenor. Counter-subject absent [E flat minor].
Bars 35-37: Answer in Treble, with Counter-subject in Alto [B flat minor].
Bar 37-39: Subject in Bass, with Counter-subject in Treble [D flat major].
Bars 39-41: Codetta, modulating from D flat major to A flat major.
Bars 41-43: Subject in Tenor, with Counter-subject (altered) in Treble [A flat major].
Bars 42-44: Stretto I. Answer in Bass. Counter-subject absent [A flat major].
Bars 46-50: Coda, establishing the Tonic key [A flat major].
Bars 48-50: Subject in First Tenor, with Counter-subject in Second Tenor [A flat major].
Exposition: Bars 1-10.
Counter-exposition: Bars 13-24.
Stretto: One (incomplete).
Coda: Bars 46-50.
- This Fugue has a “tonal” Answer, and would be called a “tonal” Fugue. The alteration in the Answer, for the sake of tonality, is made from the first to the second note.
- The Counter-subject is chromatic in character, descending gracefully by semitones. At Bars 41-42 it is broken up and made more florid, the original crotchets (quarter notes) giving way to quavers (eighth notes) and semiquavers (sixteenth notes).
- The Subject is momentarily altered by an accidental (D natural) in Bar 14, to accommodate itself to the crotchet D natural of the Counter-subject, which is here used at the 12th.
- At Bars 45-46 a Bravura passage occurs in the Bass, accompanied by short chords in the upper parts, after the fashion of the organ works.
- Episode I (Bar 10) is founded upon reminiscences of the Subject in the Tenor and Alto, with a running Bass.
- Episode II (Bar 26) in its early portion contains a series of Octave skips in the Treble, fragments of the Subject in the Bass and a running Alto. Later, fragments of the Subject, together with the running figure above-mentioned, appear in all the parts.
- In the Coda, at Bar 48, the Subject is present in its entirety in the Tenor, and ends with the final chord of the Fugue, the first part of the Counter-subject also being employed.
- At bar 49 a fifth part (second Tenor) is added up to the conclusion, in order to impart additional richness to the harmony.