Bars 1-12: Period I. Starting in F sharp minor, it briefly touches the Dominant before ending in the Tonic. Ends with a Perfect Cadence in the key of the Dominant Minor, C sharp.
Bars 12-29: Period II. Starting in the Dominant Minor, it moves to B minor (Bar 15) and the Relative Major, A (Bar 17), where it lays stress on this key by a Perfect Cadence in it (Bar 21). Ends with a Half Cadence in the key of the Dominant Major, C sharp.
Bars 29-30: Short Connecting Passage (Bass part).
Bars 30-43: Period III. Starting in the Tonic, it touches B minor (Bar 33) before returning to the Tonic area. It passes through the Dominant (Bar 37) as it prepares for the conclusion. Coda (Bars 40-43). Ending with a Perfect Cadence in the key of the Tonic, F sharp.
In the construction of this Prelude, two florid parts – freely imitating each other at certain points – are built upon a Bass of fairly staid and simple character.
Period I of the Treble of Bar 1 is answered by the Tenor in Bar 2 at the Octave below.
At the Start of Period II the Opening bars are transplanted into the key of the Dominant Minor, C sharp.
At the Start of Period II the Opening bars are reproduced in the Tonic key, the Tenor (Bar 31) answering the Treble figure as before.
Period I is capable of subdivision at Bar 7, where there is a Half Cadence on the Dominant Major, and Period II, at Bar 21, where there is a Perfect Cadence in the key of the Relative Major (A).
Period III can be subdivided at Bar 40, where the Coda commences.
Bars 1-4: Subject in Alto [F sharp minor].
Bars 4-7: Tonal Answer in Treble. No Counter-subject [C sharp minor].
Bars 7-8: Codetta, modulating from C sharp minor to F sharp minor.
Bars 8-11: Subject in Bass [F sharp minor].
Bars 11-14: Episode I, modulating from F sharp to C sharp minor.
Bars 14-16: Answer in Bass [C sharp minor].
Bars 16-19: Subject in Treble [F sharp minor].
Bars 19-28: Episode II, modulating to A and closing in Bar 20, and then proceeding through various keys to B minor.
Bars 28-31: Subject in Alto [B minor].
Bars 31-34: Episode III, modulating from B minor to C sharp minor.
Bars 34-37: Answer in Bass [C sharp minor].
Bars 37-51: Episode IV, modulating from C sharp minor, thorough G sharp minor, E major, A major, F sharp major, to B minor.
Bars 51-54: Subject in Alto [B minor].
Bars 54-57: Subject in Treble [F sharp minor].
Bars 57-60: Episode V, modulating from F sharp minor to C sharp minor.
Bars 60-63: Answer in Bass [C sharp minor].
Bars 63-66: Episode VI, modulating from C sharp minor to F sharp minor.
Bars 66-69: Subject in Treble [F sharp minor].
Bars 69-70: Coda [F sharp minor].
Exposition: Bars 1-11.
Counter-exposition: Bars 14-19.
Coda: Bars 69-70.
- 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 note to the second.
- Six Episodes:
- Episode I (Bar 11) is built up of short figures taken mostly from the first three notes of the Subject, used most often by contrary motion.
- Episode II (Bar 19) begins with a new point of Imitation proposed by the Bass (Bar 20), freely imitated by the Alto and Treble. A reminiscence of the Subject appears in the Alto in Bar 24 and the early portion of 25.
- Episode III (Bar 31) is built principally on the Subject with the addition of the figure of Episode II, which appears in the Treble.
- Episode IV (Bar 37) is built upon new material entirely. A Subject is proposed by the Alto at Bar 36 (two and a half beats before the conclusion of the Subject in the Bass), this is imitated first by the Treble and then by the Bass, at a distance of one bar from each other. At Bar 39 this subject is seen in a still more extended form in the Alto, imitated by the Bass at Bars 41-42, while it appears in an inverted form in the Treble at Bars 47-49. Fragments of the Subject are interspersed in the various parts in this Episode.
- Episode V (Bar 57) starts with a free imitation of the Treble by the Alto, with a running Counterpoint in the Bass.
- Episode VI (Bar 63) is formed of reminiscences of the Subject in the two upper parts, the running Bass being again employed.
- The culminating points of this Fugue occur at the last two entries of the Theme (Bars 60-62 and 67 to the end). In both cases the theme is accompanied in Triple Counterpoint by the figure seen in Episode II and also by that first seen in Episode IV. A more beautiful result is impossible to imagine.