By Yosef Rosenfield
In J. S. Bach’s Prelude and Fugue in C Major, there is an inserted measure presumably meant as a “correction” of Bach’s prelude that is attributed to pianist and composer Carl Czerny. Czerny seemingly noticed the movement in the bass from F sharp in measure 22 to A flat in measure 23, an interval of a diminished third, and sought to “fix” this issue by composing his own measure with G in the bass and placing it between the two. Adding this measure would theoretically remove the dissonant interval created by the adjacent measures, thereby introducing a smoother transition from the F sharp to the A flat. This editorialization, however, is made (at best) misguidedly and in fact does not improve Bach’s prelude. Given the broader framework surrounding measures 22 and 23, every musical analyst can hopefully recognize that Czerny’s measure actually runs counter to the chordal patterns that Bach reinforces and is therefore wrong in the context of this prelude.
With the opening phrase of his prelude, Bach establishes “first principles” of the piece: C, d7/C, G7/B, C. Using A minor as a pivot chord, Bach continues with ii-V-I cadences, but in the key of G major, and this time repeating the pattern with an added predominant chord in the middle: a/C, D⁷/C, G/B – CM7/B – a7, D7, G. Not only does the CM7 chord develop the ii-V-I theme in G major, which ends up being a tonicized half cadence at the end of the phrase, it also maintains a circle-of-fifths progression – a, D, G, and now C – which is another prominent motif in Bach’s prelude. Phrase number three features a direct modulation from c#º7 into a tonicized ii6 chord, d/F. This is followed by bº7/F, which is still a dominant substitution, and C/E. The phrase closes with more circle-of-fifths movement and another ii-V-I cadence: FM7/E, d7, G7, C.
By the time we reach the fourth phrase, which contains Czerny’s measure, Bach has already emphasized circle-of-fifths progressions and ii-V-I cadences as major themes in his prelude. Phrase number four starts as follows: C7, FM7, f#º, bº7/Ab. Czerny’s inserted CmM7 chord after the f#º simply does not make sense in the key and certainly does not contribute to the motivic structure of Bach’s composition. On the contrary, Czerny’s chord interrupts the circle-of-fifths progression from f#º to bº7.
The rest of the prelude indeed strengthens our previously established ii-V-I and circle-of-fifths progressions, following an extended period during which G is highlighted: G7, C/G, Gsus4, G7. After prolonging the dominant chord for a few measures, Bach finally includes another ii-V-I sequence in what is structurally a half cadence: f#º7/Eb/DP (Dominant Pedal, which is G in the key of C), C/G, Gsus4, G7. Even the last four measures, which begin and end with the concluding C major chord, contain one last ii-V-I cadence, voicing the middle chords over the Tonic Pedal (in this case C): C7, F/C/TP, d7/C/TP, G7/B/TP, C. As evidenced by these thematic progressions, Bach’s chordal structure makes it fairly obvious that Czerny’s inserted CmM7 chord has no place in this prelude.
Photo Source: Yosef Rosenfield