Bars 1-4: are devoted to establishing firmly the key of the Tonic, and preparing for the entry of the Theme upon which the Prelude is built.
Bars 4-12: Period I. Theme I (Bars 4-8). Ending with a Perfect Cadence in the key of the Dominant, B flat).
Bars 12-24: Period II. Ending with a Perfect Cadence in the key of the Relative Minor, C.
Bars 24-50: Period III. Starting in C minor, it touches B flat major (Bar 25), A flat Major (Bars 27-28), F minor (Bar 30), B flat major (Bars 31-32) before returning to the Tonic (Bar 34). The touching A flat, B flat, then C minor before ending with a Perfect Cadence in the key of the Mediant Minor, G.
Bars 50-71: Period IV. Dominant Pedal, the two parts placed upon it being in an ascending Sequence (Bars 57-60). Coda, fully establishing the key of the Tonic (Bars 69-71). Ending with a Perfect Cadence in the key of the Tonic, E flat.
The Theme upon which this Prelude is written is built mainly upon the first three notes of the figure which appears in the Bass part of the opening part.
It begins at Bar 4 and ends in the Tonic key at Bar 8. At Bars 12-16 the Theme is reproduced in full in the key of the Dominant, after which it is not again used in its entirety.
At Bars 34 a characteristic figure dropping sevenths appears in the Bass, and is responded to (in the key of the Subdominant) in Bar 37.
Bars 39-42 are in an ascending Sequence with Bars 37, 38, the characteristic drop being here widened to the interval of a tenth.
Bars 64 are in a descending Sequence with Bar 63.
Bars 1-7: Subject in Bass [E flat major].
Bars 7-13: Answer in Tenor. No Counter-subject [B flat major].
Bars 13-14: Codetta, modulating to E flat major.
Bars 14-20: Subject in Alto [E flat major].
Bars 21-27: Answer in Treble [B flat].
Bars 27-30: Episode I, prolonging the modulation to B flat major and closing in that key [B flat major].
Bars 30-36: Answer in Tenor [E flat major].
Bars 31-37: Stretto I, Subject in Bass [E flat major].
Bars 37-43: Answer in Alto [E flat major].
Bars 38-44: Stretto II, Subject in Treble [E flat major].
Bars 44-53: Episode II, modulating from E flat major, through C minor, and back to E flat [E flat major].
Bars 53-59: Subject (altered) in Tenor.
Bars 59-65: Answer in Treble [B flat major].
Bars 60-66: Stretto III, Subject in Bass [E flat major].
Bars 65-70: Coda, with final reference to a characteristic portion of Subject in the last two bars [E flat major].
Exposition: Bars 1-27.
Counter-exposition complete: Bars 30-44.
- 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.
- The length of the Subject is noteworthy; it has the effect of making the Exposition unusually long. This, however, is obviated in the Counter-exposition by taking the Subject and Answer in pairs in Stretto. By this means it is reduced to fourteen bars, or little mare than half the space occupied by the Exposition.
- Two Episodes:
- Episode I (Bar 27) is in four parts and is built upon the Subject. It serves to prolong the modulation to B flat major (i.e., the Dominant key).
- Episode II (Bar 44) is in three parts and is built principally upon figures of the Subject, but a new quaver (eighth note) figure, which first appears in Bar 43, is also added for the sake of variety.
- The keys of the Tonic and Dominant reign supreme in this Fugue. In only tow instances does it go beyond these keys; in the second Episodes, where it passes temporarily to C minor, and in the Tenor entry in Bar 53, the first notes of which would naturally be A, but it is here altered to B in order to accommodate itself to the harmony around it.