Bars 1-8: Period I. Tonic Pedal (Bars 1-5), followed by a Dominant Pedal (Bars 5-7). Ending with Perfect Cadence in the key of the Dominant, B.
Bars 9-24: Period II. Staring in B major, it touches F sharp minor and C sharp minor (Bars 10-11) before settling in the Dominant (Bar 17). Dominant Pedal (Bars 18-21). Coda, firmly establishing the key of the Dominant (Bars 18-24). Ending with a Perfect Cadence in the key of the Dominant, B; double bar.
Bars 25-32: Period III. Starting in the Dominant, it gradually curves round to C sharp minor, remaining there. Ending with Perfect Cadence in the key of the Relative Minor, C sharp.
Bars 32-54: Period IV. Moves from the Relative Minor to the Dominant (Bar 35), before returning to the Tonic (Bar 37). Descending Sequence (Bars 37-40). Tonic Pedal (Bars 46-49 and 51-54). Coda, firmly clenching the key of the Tonic (Bars 46-54). Ending with Perfect Cadence in the key of the Tonic, E.
This Prelude has two main divisions separated by the double bar.
Bars 5-8 are a reproduction in the key of the Dominant of Bars 1-5, the order of the upper parts being reversed, the Bass in each standing as a Pedal.
At Bars 18-21, the two upper parts are in a descending Sequence with each other, and are placed upon the Dominant Pedal. (Compare Bars 46-49, where similar work is placed upon the Tonic Pedal.)
The second division of the Prelude (Bar 25) starts with a transposition of the opening bars bodily into the key of the Dominant, the three figures being assigned to the same part as the commencement.
Period I is capable of subdivision at Bar 5(.5).
Period II is capable of subdivision at Bar 18.
Period IV can be divided similarly to Period II at Bar 46.
The first three bars of the second Coda (Bars 46-49) are a transposition into the Tonic key of the corresponding Bars (18-21) of the Coda, in the first part of the movement.
Four Themes all contrasted with each other are employed in this Prelude for imitative work, Theme I being the most important.
In the concluding bars of both divisions a fourth part is added to the harmony for the sake of richness of effect.
This Prelude is obviously cast in the mould of early Binary form. It is cut nearly in half by the double bar, and immediately afterwards the opening material makes its re-appearance transposed into the key of the Dominant. The Coda in the first part of the movement, the early portion of which is built on the Dominant Pedal, is transposed in the second part and placed upon the Tonic Pedal. Theme IV (Bar 32, Alto part) was evidently designed to play an important part in the unification of the movement, its first three semiquavers (sixteenth noes) forming a reminiscence of the big Theme (Theme I), and these are kept prominent by similar and contrary motion until the Coda is reached.
Bars 1-2: Subject in Bass [E major].
Bars 2-4: Real Answer in Tenor, with Counter-subject in Bass [B major].
Bars 4-5: Subject in Alto. Counter-subject in Tenor [E major].
Bars 5-7: Answer in Soprano. Counter-subject in Alto [B major].
Bars 7-9: Episode I, modulating from E to B.
Bars 9-10: Answer in Alto. Counter-subject absent [E major].
Bars 9-11: Stretto I. Subject in Tenor [E major].
Bars 10-12: Answer in Bass [E major].
Bars 11-12: Subject in Treble. Counter-subject in Tenor [E major].
Bars 12-16: Episode II, modulating from E through F sharp minor to C sharp minor, with close.
Bars 16-17: Subject in Alto [C sharp minor].
Bars 17-18: Stretto II. Answer in Treble. Counter-subject absent [E major].
Bars 19-20: Subject in Bass [B major].
Bars 20-21: Stretto III. Answer in Tenor. Counter-subject absent [F sharp minor].
Bars 22-26: Episode III, modulating from F sharp minor to C sharp minor.
Bars 26-27: Subject in Treble by Diminution. Counter-subject absent [E major].
Bars 27-28: Stretto IV. Subject in Alto by Diminution. Counter-subject absent [E major].
Bars 28-29: Subject in Tenor by Diminution. Counter-subject absent [B major].
Bars 28-29: Answer in Bass by Diminution. Counter-subject absent [B major].
Bars 30-31: Subject in Bass by Diminution. Counter-subject absent [B major].
Bars 30-32: Subject in Alto.
Bars 32-35: Episode IV, modulating to G sharp minor and closing in that key.
Bars 35-36: Answer in Alto. Subject in Tenor by Inversion and Diminution [E major].
Bars 35-38: Stretto V. Subject in Tenor. Counter-subject in Treble [E major].
Bars 36-38: Answer in Bass. Counter Subject in Alto [B major].
Bars 37-39: Subject in Treble. Counter-subject in Tenor [E major].
Bars 39-40: Codetta, confirming the key.
Bars 40-41: Answer in Bass. Counter-subject in Alto [B major].
Bars 41-43: Coda.
Exposition: Bars 1-7.
Counter-exposition: Bars 9-12.
- This Fugue has a “real” Answer, and would be called a “real” Fugue.
- The Counter-exposition is a complete one – i.e., all voices take part in it. It is worked in Stretto, thus adding to its interest as well as saving space. The Treatment in Prelude No. VII, Book II, is exactly the same.
- The Counter-subject disappears for a considerable time after the Exposition. It is, however, resumed at Bar 36 (Treble part), and from this point accompanies every entry of the Theme to the end of the Fugue.
- The first and fourth Stretti are complete. The second, third and fifth are incomplete. The fifth Stretto (Bar 35) is very remarkable, the three lower parts are all entering at different distances, while at the same time the Treble has the Theme both in Inversion and Diminution, and in Bar 36 adds a bit of the Counter-subject in its original form.
- Three Episodes:
- Episode I (Bar 7) is built upon reminiscences of the Counter-subject treated in free imitative Counterpoint.
- Episode II (Bar 12). In this a short figure of crotchets (quarter notes), together with a minim (half note) suspension taken from the Counter-subject, is proposed by the Treble (Bar 12) and imitated by the Alto, Bass, and Tenor.
- Episodes III and IV. In these, reminiscences of the Subjects are noticeable, sometimes by Diminution and Inversion combined.