V. Chromaticism
The Omnibus Progression
Bryn Hughes
KEY TAKEAWAYS
The omnibus progression is a chromatic voice-leading technique that moves in contrary motion.
- The progression includes two voices that move participate in a voice exchange, while the other voices remain static
- This progression prolongs dominant harmony
- In the converging omnibus progression, the leading tone descends while the bass (which starts on the root) ascends
- In the diverging omnibus progression, the seventh ascends while the bass (which starts on the root) descends
- Both patterns can go through multiple iterations by “resetting” the progression when you reach another root-position dominant-seventh chord
The omnibus progression is a special type of chromatic sequence in which the bass and another voice in the texture move in contrary motion. The omnibus progression is most commonly used to prolong dominant harmony, but it can also be used as a means of modulating into distant keys.
There are two ways of writing an omnibus progression: with the bass and upper voices converging, or with the bass and upper voices diverging.
The converging omnibus progression
The converging omnibus progression begins on a root-position dominant-seventh chord. The bass moves upward by semitone, while the voice with the leading tone moves downward by semitone, creating a voice exchange. The voice leading in this progression should be as smooth as possible: The only voices that are moving are the ones involved in the voice exchange. The other voices remain static as common tones.
shows the prolongation of a dominant-seventh chord via a voice exchange between the leading tone (in the soprano) and the root of the chord (in the bass). Moving three semitones in this fashion brings you to another root-position dominant-seventh chord/German augmented-sixth chord (recall that these are enharmonically equivalent!). Moving four semitones in this fashion brings you to the same dominant-seventh chord on which you began the progression, but this time, in first inversion. The pattern yields five different chords, labelled 1-5 in the example below.
One variation of the omnibus progression that some composers use is to change the second chord in the pattern from a dominant-seventh chord to a diminished-seventh chord. In this version, there are three common tones held between the first and second chord. You can see this variation in
Brahms provides us with a good example of a converging omnibus progression. In
, we can see that the dominant chord in the key of B major is prolonged by way of an omnibus progression in mm. 38-41. Interestingly, he uses the progression again in mm. 46-48, this time to prolong the dominant of the new key of C♯, which is the key “implied” by the internal chords of the original progression in mm. 38-41.
The omnibus progression can be used to move into distant keys, and eventually traverse the entire octave (though in practice it is rare to go through the entire octave). Once you reach the new root-position dominant-seventh chord (that you arrived at after four chords), find the new leading tone and begin the process again. In
below, the sequence “resets” with every fourth chord, reinterpreting that as a new dominant-seventh chord and thus moving a new leading tone in contrary motion with the bass (which is on the root of the chord). For example, the fourth chord in the pattern is B♭7. In Example 1, this chord was interpreted as a German augmented-sixth chord, and the chromatic voice exchange continued one more semitone to reach the dominant of C in first inversion (Chord 5 in the example above). This time, we are starting the pattern over by interpreting the B♭7 as a new root-position dominant-seventh chord, and moving the new leading tone in a chromatic voice exchange with the bass. This chord has been re-labeled as Chord 1, with the new leading tone highlighted in blue. The colours throughout the example below show the the reinterpretations of this chord throughout the pattern, and the voice exchanges between the bass and the various leading tones.
In
below, Chopin uses the omnibus progression through two iterations, which you can follow by observing the red and blue noteheads and numbers listed above the staff. Chopin uses the variant with the diminished-seventh chord as Chord 2, and moves through the omnibus progression from a root-position dominant-seventh chord in C♯ minor to a root-position dominant-seventh chord in G major. Interestingly, though, Chopin then takes this D7 chord and moves both the root and fifth down by semitone to become the root and fifth of the A♭7 chord which serves as the dominant to close the phrase in D♭ major, the same tonic (but not mode) that we started on!
The diverging omnibus progression
The diverging omnibus progression works almost identically, but instead of moving the leading tone in contrary motion to the bass, you move the seventh. This is shown in
. To move into distant keys, find the new seventh in the root-position dominant-seventh chord and repeat the process. Again, this is made more clear by following the colours in the example, which represent each voice exchange between seventh and bass. For instance, starting on G7 in measure 1, the chromatic voice exchange occurs between F in the alto voice, and G in the bass. Moving apart in contrary motion by semitone, we eventually reach E7 on beat 4 of the same measure. At this point, we have a new seventh of the chord, D, which participates in the voice exchange with the bass, which is now on E. Another way to think of this version of the omnibus progression is to consider it starting on Chord 4 of the pattern. If you wanted to completely reverse the original omnibus progression from Example 1, you would simply insert Chord 5 before any of the Chord 4s listed in the example below. This kind of reversal can be found in the excerpt from Schubert’s Piano Sonata, reproduced below in .
Much like the converging version of this technique, the diverging omnibus progression is rarely used to traverse the entire octave, but we do find many examples in which the technique is used to achieve modulations into distant keys. In
, Mussorgsky uses the omnibus progression to modulate to E major by way of two iterations through the pattern.
When two voices "switch notes," exchanging with one another. For example, a soprano singing C moves to E, while a bass singing E moves to C would be considered a voice exchange between the soprano and bass.