Other Chromatic Harmonies
We now examine several other chords that can be found within the tonal music system that do not fit any of the previous categories of chromatic harmony. While these chords are not as common as the other chromatic chords we have studied, they are used with some frequency in music of the Romantic period. Except for the cto7 chord, they can all be used as substitutes for diatonic harmonies.
Dominant with Substituted 6th
The first of these harmonies is not technically a chromatic chord because it merely involves the substitution of scale degrees in the diatonic scale. In the dominant chord with substituted 6th, the 6th above the root is substituted for the 5th above the root. You can simply “unplug” the 5th of the dominant chord and insert the 6th above the root in its place. Decades ago, some theorists used to recognize this as a iii6 chord, but in modern theory we do not do so because of the strength of the dominant motion in the bass. The Vsubs 6th substitutes for V and V7 chords, and can be approached with subdominant harmonies, including secondary dominants.
The V subs 6th can also be used in minor keys, and the result in an augmented chord sound type.
The dominant seventh with substituted 6th (V7 subs 6th) is also found. The resolution of the substituted 6th is typically by leap down to the tonic, and the seventh of the chord will resolve down by step.
Augmented Dominant Chords
Although the augmented mediant triad exists within the harmonic minor scale, the III+ chord is not used in tonal harmony. The augmented sonority, however, is sometimes used as a dominant function. Augmented dominant chords (V+) are built by raising the fifth of a regular dominant chord, which forms the leading tone to the third of the tonic chord in major keys. A m7 can be added to the V+ to create the V+7, and this chord is also used with some frequency. In part-writing, the seventh of the chord resolves down, the raised fifth resolves up to the third of the next chord, and the resolution of the leading tone can be either up to the tonic – if the leading tone is an outer voice – or down to the fifth of the next chord if the leading tone is in an inner voice.
Note that in a V+ in minor mode the altered note is enharmonically the same note as the resolution, which is the reason this chord is not used in minor keys. Observe also that the resulting sonority is identical with the dominant with substituted 6th, which can function in minor keys because the resolution is different.
Augmented dominants and augmented dominant seventh chords can also occur as secondary functions, for example V+/IV and V+7/IV.
Common Tone Diminished Seventh Chords
Common tone diminished seventh chords (cto7) have a weak harmonic function and should be viewed as embellishing chords or decorations for the stronger functional harmonies around them. Common tone diminished seventh chords progress to either major triads or Dom7 (Mm7) chords, which are themselves most often either tonic or dominant harmonies within the key and which may be inverted. The root of the major or Dom7 chord to which the cto7 is progressing is a common tone with one of the notes in the cto7. Technically, the cto7 can be spelled in any fashion, but they are usually spelled with the common tone as the 7th of the cto7 chord and with stepwise motion in the other voices. Another way of looking at cto7 chords is as a collection of chromatic and diatonic neighbor or passing tones that by happenstance form a o7 chord.
Follow these steps to write cto7 chords:
- Find the root of the chord that you are embellishing and make that the common tone.
- Spell a diminished seventh chord using this common tone as the seventh.
- The other notes of the cto7 chord will form upper and lower neighbors to the embellished chord.
When part writing common-tone diminished chords in an SATB texture, the goal should be smooth voice leading, although leaps in inner voices are acceptable. An alternate to leaping is to double the fifth of the chord the cto7 is embellishing, as shown in the next examples.
While not common in tonal music, ninth chords do occur beginning in the late Classical era. In most cases, what may be perceived as a ninth chord is merely an NCT that resolves or “dissolves” into a seventh chord. In the following example, the 9th is treated as an NCT and resolves down to the G prior to the resolution to the I chord.
In Schumann's song Ich Grolle Nicht, a borrowed iiØ7 in m. 3 moves to what at first appears to be a V♭9, but the ninth resolves into the texture at the end of the measure, showing that it is just a 9-8 suspension.
When the resolution of the 9th is delayed until the next chord, the result is clearly an actual 9th chord rather than an NCT.
The V9 (MmM) is the diatonic dominant ninth in major keys. In minor keys the V♭9 (Mmm) is found, and this sonority can be created in major by borrowing the ♭6. Whether in major or minor modes, the V♭9 (Mmm) is the most common type of dominant ninth.
Nondominant ninths are rarely used in tonal music. The most usual nondominant ninths are based on the supertonic (ii9) and subdominant (IV9 or iv9) scale degrees. Other uses of 9th chords and similar “tall chords” are discussed later in 20th Century Harmony.
Enlarged Chart of Harmonic Progression
The addition of secondary dominant and leading tone chords, borrowed chords, augmented sixth chords, and the various chords found in this chapter greatly expands the possibilities within the chart of harmonic progression. The following chart, while not exhaustive, does illustrate the rich selection of chords available within tonal music since the dawn of the Romantic period.