Bach: Prelude and Fugue

Watson Li

Bach's Praeludium 21 is assembled in two main components: a rapid prelude and a more complicated fugue. Praeludium 21 is one of Bach's Great 48: two series of fugues (and their corresponding preludes) which were written in all of the twenty-four major and minor keys.

The prelude itself is in two parts. It is rather toccata-like, and features a quick tempo and beat with a single voice. The melody comes through in a pattern of repeated broken four-note chords, and occasionally exhibits scale passages with 32nd note runs. Although a evenly-distributed beat is used throughout the majority of the piece, in certain sections (such as measure 11) the rhythm changes into an arpeggiated dotted rhythm. The speed at which these cadenzas are played are meant to bring out the virtuosity of the player. Approximately midway into the prelude, the key changes from B flat major to F major in a bridge that connects the first portion into the second.The second part of the prelude features significanly more scale runs than the first part and also includes some blocked 7th chords. A coda is seen at bar 18 following the second part and the coda exhibits traits from the first section of the prelude as well as some additional ornaments. The prelude ends with a pattern of climbing broken four-note chords.

After the prelude comes the fugue. Fugue 21 is a tonal fugue in three voices and three main components: an exposition (measures 1-17), modulatory section (measures 17-41), and a recapitulation (measures 41-48). The exposition starts off with the subject in B flat major in the soprano range. What is notable about this subject is the fact that it is unusually long; in fact, the subject of this fugue can be divided into two parts, the first being a disjunct motif and the second being a conjunct motif. As soon as the subject is played once, the first counter-subject in F major, also in the soprano range, is played by the right hand as the tonal answer in the dominant key is expressed in the alto range by the left hand. These two voices again end directly as the subject comes back in the bass range as the first counter-subject is played in the alto and the second counter-subject is played in the soprano range in B flat major as well. Again, these end in four measures and a new series of three come on: the final three before entering the modulatory section of the fugue. They are the answer, in the soprano range, the second counter-subject in the alto range, and the first counter-subject in the bass range. It should also be noted that there are several special parts to the exposition: in the first counter-subject, Bach places a series of tied and repeated notes as well as a set of chords in the second counter-subject. The modulatory section is comprised of the three voices as well as two episodes that do not seem to fit under any particular voice category. The first episode is introduced from bars 17 to 22, and it is derived from part of the conjunct motif found in the subject. The key of the piece changes over from F major to G minor during the first episode. The first episode also plays the reverse of the disjunct motif in the subject with the left hand in measures 19 to 22. After the first episode is played, the voices come back with the first counter-suibject in G minor being played in the soprano, the subject in G minor in the alto, and the second counter-subject, also in G minor, in the bass. These morph into the second counter-subject in C minor in the soprano, along with the first counter-subject in C minor in the alto and the answer in C minor in the bass. The second episode follows in measures 30 to 35, transitioning from C minor to G minor and back to C minor. It is an inversion of the first episode, and the three voices resume once again in measure 36. The voices continue to switch, with the first counter-subject continuing all the way through in E flat major until the recapitulatory section. The subject carries through in the alto range in the key of B flat major, accompanied by the first counter-subject in the soprano and the second counter-subject in the bass, both in B flat major as well. The fugue approaches its end starting at bar 45, where it once again plays the motif in the second part of the subject, with the repeating notes. An echo of the subject is seen until the fugue ends with a perfect cadence.