Bars 1-26: Period I. Tonic Pedal (Bars 1-3 and 6-8). Touches F major and B flat Major (Bars 11-13) before returning to the Tonic region (Bar 15). Ending with a Perfect Cadence in the key of the Dominant Minor, A.
Bars 27-61: Period II. Dominant Pedal (Bars 26-29 and 43-46). Descending Scale of A minor (Bar 34). Here it moves away, touching G minor (Bar 36), and curving round to D minor. Ending with a Perfect Cadence in the key of the Tonic, D.
Bars 57-61: Coda and Tonic Pedal.
This Prelude divides into two nearly equal halves, the first half ending in the Dominant Minor (A), and the second half ending in the Tonic (Bar 57), the five concluding bars being a short Coda, serving to clench the Tonic key.
Bars 5-8 Re a reproduction of Bars 1-4, the parts being Inverted with regard to each other, the Tonic Pedal upon which these bars are built effectually establishing the key.
At Bars 13, a new contrasted figure is introduced in the Bass, which is freely imitated in the two parts alternately every bar, up to Bar 18. This figure is not employed in the second part of the movement.
At Bar 26, the opening bars, Inverted as to the two parts, are transposed into the Dominant minor (A), the same reproduction being observable (by inversion) as in the opening of the movement.
Bars 1-3: Subject in Alto [D minor].
Bars 3-5: Real Answer in Treble, with Counter-subject in Alto [A minor].
Bars 5-6: Codetta, modulating from A minor to D minor.
Bars 6-8: Subject in Bass [D minor].
Bars 8-10: Episode I, modulating fro D minor, through F major, and back to D minor.
Bar 10: Subject in Bass (first portion only). Counter-subject absent [D minor].
Bars 10-12: Subject in Treble (incomplete). Counter-subject absent [D minor].
Bars 12-14: Episode II, modulating from F major to D minor.
Bars 14-15: Subject in Alto. Counter-subject absent [D minor].
Bars 14-16: Stretto I, Answer in Treble. Counter-subject in Bass [A minor].
Bars 16-17: Codetta, modulating from A minor to D minor.
Bars 17-18: Answer in Alto by Inversion. Counter-subject absent [D minor].
Bars 17-18: Stretto II, Subject in Bass by Inversion. Counter-subject absent [G minor].
Bars 18-19: Subject in Bass (fragment). Counter-subject absent [G minor].
Bars 18-19: Stretto III, Subject in Treble. Counter-subject absent [G minor].
Bar 25: Subject (fragment) in Alto. Counter-subject absent [D minor].
Bar 25: Subject (fragment) in Bass by Inversion. Counter-subject absent [D minor].
Bars 25-27: Stretto IV, Subject in Alto, Subject in Treble, half-a-bar apart.
Bars 26-27: Counter-subject in Bass [D minor].
Exposition: Bars 1-8.
- This Fugue has a “real” Answer, and would be called a “real” Fugue.
- The Subject is only twice used after the Exposition in its complete form (Bars 14 and 25). On all other occasions it is considered curtailed.
- The Counter-subject entire disappears after the Exposition, except on two occasion (Bar 14 and 26), both times appearing in the Bass. Whenever the Subject is used in an incomplete form, the Counter-subject is absent, a free complementary part supplying its place.
- The first three Stretti are incomplete – i.e., all the parts are not employed in them. The fourth Stretto is complete as far as the several parts are concerned, though in all but one part the Subject is incomplete.
- Three Episodes:
- Episode I (Bar 8). A new figure is started in the Bass in Bar 8, which is freely imitated by the Treble in the same bar and by the Alto in the next.
- Episode II (Bar 12) is built upon the same figure as Episode I.
- Episode III (Bar 19) is for two bars and a half built mainly upon the early part of the Subject by Inversion, when at Bar 21 the Alto makes an initiatory curve inclining to the use of material employed in the previous Episodes; this suggestion is immediately grasped by the Treble and Bass.