Two Themes are employed for the most important work in this Prelude:
- Theme 1 (Bars 1-4).
- Theme 2 (Bars 29-31).
Bars 1-17: Period I. Ending with a Perfect Cadence in the key of the Dominant, C sharp.
Bars 17-29: Period II. Ending with a Half Cadence in the principle key, F sharp.
Bars 29-45: Period III. Ending with a Perfect Cadence in the key of the Relative Minor, D sharp.
Bars 45-57: Period IV. Ending with a Cadence in the key of the Tonic, F sharp.
Bars 57-68: Period V. Starting with a Reproduction of the Opening bars and ending with a Perfect Cadence in the key of the Tonic, F sharp.
Bars 68-75: Coda. Further clenching the Tonic key.
This Prelude is constructed with immense care, the fineness of the work throughout being remarkable; moreover, the interest of both parts is very evenly kept up, neither part having more than a momentary precedence of the other.
Period I starts with figures which firmly plant in the mind of the Tonic key.
Period II begins in the key of the Dominant, with a variation of Theme I.
Period III introduces another important Theme (Theme II), which appears in the Tonic key in the upper part (Bar 29), balancing the figure previously used in the Dominant key in the previous Period. This is answered by the Bass at the fifth below (Bars 30-34).
Period V contains the reproduction of the Opening bars in the Tonic key with a slight ornamentation of Bar 1. At Bars 60-65 a free version appears in the Bass part of the figure which was used in the early part of the movement (Bars 7,8).
Additional parts are added in the concluding bars for the sake of enriching the harmony.
Bars 1-4: Subject in Alto [F sharp major].
Bars 4-8: Real Answer in Treble, with Counter-subject in Alto [C sharp major].
Bars 8-12: Subject in Bass, with Counter-subject in Treble [F sharp major].
Bars 12-20: Episode I, modulating from F sharp, through D sharp minor, G sharp minor, and back to F sharp.
Bars 20-24: Subject in Treble, with Counter-subject in Bass [F sharp major].
Bars 24-32: Episode II, modulating from F sharp to C sharp.
Bars 32-36: Answer in Bass, with Counter-subject in Alto [C sharp major].
Bars 36-40: Subject in Alto, with Counter-subject in Bass [F sharp major].
Bars 40-44: Subject in Treble, with Counter-subject in Alto [D sharp minor].
Bars 44-52: Episode III, modulating from D sharp minor to B major.
Bars 52-56: Subject in Alto, with Counter Subject in Treble [B major].
Bars 56-64: Episode IV, modulating from B to F sharp.
Bars 64-68: Subject in Bass, with Counter-subject in Treble [F sharp major].
Bars 68-70: Codetta, modulating from F sharp major to C sharp major.
Bars 70-74: Answer in Alto. Counter-subject absent [C sharp major].
Bars 74-76: Codetta, modulating from C sharp major to F sharp major.
Bars 76-80: Subject in Treble. Counter-subject in Alto, slightly altered in its third bar [F sharp major].
Bars 80-84: Coda [F sharp major].
Exposition: Bars 1-12.
Counter-exposition: Bars 32-40.
Coda: Bars 80-85.
- This Fugue has a “real” Answer, and would be called a “real” Fugue.
- The Counter-subject is divisible into three small sections, marked off by rests between them. At Bar 32, where it accompanies the Answer in the Bass, it is treated exceptionally, its third section being transferred to the Treble (Bar 34-35).
- It is absent on one occasion, at Bar 70, where it might have been expected in the Bass part.
- Two Episodes appear before the Counter-exposition is reached. The reason is that after placing the Subject in the Treble in the original key (Bar 20) after the first Episode, it required another Episode to make the necessary modulation to the key of the Answer which starts the Counter-exposition (Bar 32). The above Subject in the Treble is merely a redundant entry, giving an opportunity for the Counter-subject to appear below it, whereas up to this point it had appeared only above it.
- Episode I. This is composed entirely in Triple Counterpoint. The figures are new, with the exception of a slight reminiscence of the Subject. (Compare the Treble at Bar 14 with Bars 2-3 of the Alto.) Three different positions of the three constituent themes are used, the first being in Bar 12; the second in Bar 14; and the third in Bar 16.
- Episode II (Bar 24) is less important from a contrapuntal point of view. It is built from the first and second sections of the Counter-subject, with a running Bass.
- Episode III (Bar 44). This is built upon precisely the same material as Episode I, but it is used in three entirely new position, the first beginning at Bar 44; the second at Bar 46; and the third at Bar 48. Thus all the six possible positions of the triple Counterpoint are employed in Episodes I and III.
- Episode IV (Bar 56) is exactly similar in construction to Episode II. The area covered by the four Episodes is 32 bars, an equal share being alloted to each.