melody by sharpening the fourth note from a B to a B, a modification already found in 17th-century hymnbooks. This change also allowed Bach to introduce dissonances, imbuing the work with what the French organist and musicologist Norbert Dufourcq called "tormented chromaticism". The quaver countersubject and its inversions are used and developed throughout the fugue. It resembles some of Bach's other keyboard fugues, in particular the antepenultimate fugue in B minor BWV 891/2 of the second book of The Well-Tempered Clavier, composed at roughly the same time. The inversion of the countersubject in bar 5, omitting the first note, plays a significant role later in the fugue (bar 30): The stretti occur at intervals of varying length; in addition to the fugue subject, there are also imitations and stretti both for the semiquaver figure in the subject (and its inversions) and the figure above derived from the countersubject. has given the following summary of the stretti for the fugue subject: bars 1–2: between tenor and alto, one and a half bars later bars 7–8: between soprano and bass, one and a half bars later bar 10: between alto and soprano, 1 crotchet later bar 16: between alto and tenor, a minim later bars 23–24: between bass and tenor, a bar later bars 36–37: between alto and soprano, 5 crotchets later bars 37–38: between soprano and tenor, one and a half bars later bar 57: subject simultaneously in crotchets in alto and augmented in minims in tenor The last entry of the fugue subject in the tenor voice gives the impression of the return of a conventional cantus firmus; the coda over the tenor's sustained F is built on the motifs of the countersubject. The different types of stretti result in a large variety of harmonisations of the theme and musical textures throughout the chorale prelude. has given a detailed analysis of BWV 689 from the perspective of Bach's keyboard fugues: Section 1 (bars 1–18). The fugue starts in a measured way, as if under a burden, the four entries effectively spaced out over regular units of bars. The tenor is followed in stretto 6 beats later by the alto and then similarly the soprano by the bass. Before the bass subject ends on the first beat of bar 11, a second set of fugal entries begins, this time more anguished, more dissonant, due to the irregularity of the stretti. The