V. Chromaticism

Common-Tone Chords (CTº7 & CT+6)

Brian Jarvis

Key Takeaways

• o7 ($\mathrm{CT^{o7}}$ and $\mathrm{Ger^{+6}}$ ($\mathrm{CT^{+6}}$) chords that embellish the upcoming chord (a major triad or dominant seventh chord, typically $\mathrm{I}$ or $\mathrm{V})$
• Can either be used as a complete or incomplete neighboring chord
• Have a common tone with the chord being embellished
• That common tone is the root of the chord being embellished
• In four voices, the fifth of the embellished chord is often doubled.

The common-tone diminished seventh chord $(\mathrm{CT^{o7}})$ and common-tone augmented sixth chord ($\mathrm{CT^{+6}}$) represent a completely different usage of two chords with which you are already familiar: $\mathrm{vii^{o7}}$ and $\mathrm{Ger^{+6}}$ . Whereas these chords typically function in a more progressive harmonic context, when employed as common-tone chords, they serve a purely embellishing function and are the result of the culmination of multiple, simultaneous neighbors tones. Common-tone chords share a common tone with the chord being embellished, whereas a $\mathrm{vii^{o7}}$ and $\mathrm{Ger^{+6}}$ do not. (NOTE: $\mathrm{Ger^{+6}}$ typically resolves to a $\mathrm{cad.^6_4}$, which does have a common tone with the $\mathrm{Ger^{+6}}$, but remember that the $\mathrm{cad.^6_4}$ is not the actual destination chord, it’s a delay of the actual chord which is a dominant chord in root position – a normal $\mathrm{Ger^{+6}}$ does not have any common tones with the dominant chord being embellished). You can expect the embellished chord will either be a major triad or sometimes a dominant seventh chord and the Roman numeral to be either $\mathrm{I}$ or $\mathrm{V}$. Minor triads can be embellished in this way too but are far less common so this chapter will focus on major triads and dominant seventh chords only. To construct a common-tone chord for a minor triad, the process is the same except that the third of the chord will also be a common tone.

Deriving a CTo7 chord from multiple neighbor tones

Example 1 goes through the conceptual process of producing a $\mathrm{CT^{o7}}$ chord through the layering of simultaneous neighbor tones. The first system presents a single tonic chord and each three-measure unit expresses a single neighbor tone. The second system combines two neighbor tones from system 1 but they are still a single tonic chord throughout, just with two neighbors instead of one. The final system shows all three neighbors combined into a single chord and is an example of a $\mathrm{CT^{o7}}$ chord. Notice that the chord in the middle has a fully diminished quality, but if you try to wrangle it into being some type of $\mathrm{vii^{o7}}$ chord, you’ll come up with $\mathrm{vii}^{\circ}\begin{smallmatrix}4\\2\end{smallmatrix}/\mathrm{iii}$. The problem is, there is no $\mathrm{iii}$ chord to be found so that analysis wouldn’t represent this music accurately.

Example 1. Demonstration of the conceptual process of how multiple neighbor tones can come together to form a $\mathit{CT^{o7}}$ chord.

Creating a CTo7 chord

Creating a $\mathrm{CT^{o7}}$ chord is a little different than spelling a traditional chord because it doesn’t have a root (simlar to augmented sixth chords). To build one, focus on the neighboring aspect of the chord. In Example 1, notice that the root of the resolving chord is the common tone so you know that note will be included. Then notice that the fifth of the chord has been doubled (which is very common) and that one of the chordal fifths is embellished by its upper neighbor (G–A–G) and the other is embellished by its lower neighbor (G–F♯–G). Finally, look at how the third of the chord is embellished by its lower neighbor (E–D♯–E). You can create a $\mathrm{CT^{o7}}$ chord by going through the following procedure:

• Find the root of the chord you want to embellish (this will be the common tone)
• Find the upper and lower neighbors to the fifth of the embellished chord
• The upper neighbor will involve a whole step (major 2nd)
• The lower neighbor will involve a half step (minor 2nd in particular)
• Find the lower neighbor (minor 2nd in particular) of the 3rd of the embellished chord.

Recoginizing CTo7 when analyzing

Finding this chord in context involves determining the presence of fully diminished 7th chords which can be done as part of a lead-sheet style analysis. Then for each fully diminished 7th chord you find, determine if it and the chord it resolves to have a common tone between them. If it doesn’t, then it should be some form of $\mathrm{vii^{o7}}$ or an applied $\mathrm{vii^{o7}}$ chord. If it does have a common tone, then it is a $\mathrm{CT^{o7}}$ chord with ONE COMMON EXCEPTION! The common exception involves the $\mathrm{cad.^6_4}$ (as mentioned above). Remember the $\mathrm{cad.^6_4}$ is not the actual chord, it is an embellishment of the root-position dominant chord being embellished. So, make sure to look past the $\mathrm{cad.^6_4}$ to its $\begin{smallmatrix}(7)\\5\\3\end{smallmatrix}$ resolution to determine if there is a common tone (see Example 2).

Example 2. The $\mathit{cad.^6_4}$ can produce a common-tone that does not relate to $\mathit{CT^{o7}}$ chords.

Resolving CTo7 to V7

a $\mathrm{CT^{o7}}$ chord may resolve to $\mathrm{V^{7}}$ instead of $\mathrm{V}$. Example 3 shows the sol–la–ti $(\hat{5}-\hat{6}-\hat{7})$ voice leading that replaces the sol–la–sol $(\hat{5}-\hat{6}-\hat{5})$ line that occurs in the triad-only version.

Example 3. Comparison of a complete neighbor $\mathit{CT^{o7}}$ that resolves to $\mathit{V}$ and to $\mathit{V}^{7}$.

CTo7 with incomplete neighbors

While the $\mathrm{CT^{o7}}$ chord is often preceded and followed by the same chord (producing multiple, complete neighbor tones), this is not always the case. Sometimes, incomplete neighbors are used instead. The complete-neighbor examples had some chord, $x$, the actual $\mathrm{CT^{o7}}$ itself, followed by $x$ again. However, $\mathrm{CT^{o7}}$ chords may be preceded by a different chord, $y$, producing the following progression: $y-\mathrm{CT^{o7}}-x$. The example below demonstrates this situation. Notice that the first $\mathrm{CT^{o7}}$ is surrounded by different chords $\mathrm{(I}$ then $\mathrm{V^4_3)$. The arrow shows which chord the $\mathrm{CT^{o7}}$ is embellishing. Just like complete neighbor $\mathrm{CT^{o7}}$ contexts, the embellished chord is the one to focus on, not the preceding chord. This progression is an elaboration of the $\mathrm{I-V^4_3-I^6}$ progression that you’ve encountered with tonic prolongation but with $\mathrm{CT^{o7}}$ chords filling in the space between each chord providing a much more colorful version of what was a rather simple progression. When listening to the example, try to hear the underlying $\mathrm{I-V^4_3-I^6}$ progression as its underlying model.

Example 4. A tonic expansion pattern elaborated by two different $\mathit{CT^{o7}}$ chords comprised of incomplete neighbors.

Creating a CT+6 chord

The other category of common-tone chords you’ll encounter (especially in music of the later 19th century) is a German augmented sixth chord ($\mathrm{Ger^{+6}}$) that functions, like the $\mathrm{CT^{o7}}$, in a embellishing capacity. The effect is similar to the $\mathrm{CT^{o7}}$ but a little darker in affect because all three neighbor tones are chromatic in this version instead of just two with $\mathrm{CT^{o7}}$ chords. In short, build a $\mathrm{CT^{o7}}$ and use a minor 2nd neighbor above the fifth of the chord instead of a major 2nd above like the $\mathrm{CT^{o7}}$ uses. Here’s the procedure for spelling this chord:

• Find the root of the chord you want to embellish (this will be the common tone)
• This is more than likely going to be tonic with $\mathrm{CT^{+6}}$ chords
• Find the upper and lower neighbors to the fifth of the embellished chord
• The upper neighbor will involve a half step (minor 2nd)
• The lower neighbor will involve a half step (minor 2nd in particular)
• Find the lower neighbor (minor 2nd in particular) of the 3rd of the embellished chord.

When a $\mathrm{CT^{+6}}$ chord is embellishing a I chord (which is usually the case), you can think in terms of solfege to find the notes. The solfege you need would be the same as that of a $\mathrm{Ger^{+6}}$ chord: le–do–me/ri–fi $(\downarrow\hat6-\hat1-\downarrow\hat3/\uparrow\hat2-\uparrow\hat4)$. Because this chord is most often found in major keys, ri $(\uparrow\hat2)$ would be a better spelling than me $(\downarrow\hat3)$.

Example 5 below shows both chords ($\mathrm{CT^{o7}}$ and $\mathrm{CT^{+6}}$) for comparison. Note that the common tone is not always the bass note and that the +6th interval may be inverted to become a °3rd instead, but the chord is typically labeled $\mathrm{CT^{+6}}$ in both contexts.

Example 5. Comparison between a $\mathit{CT^{o7}}$ and $\mathit{CT^{+6}}$ chord, both as complete neighbors.

Musical Example

The introduction to Scott Joplin’s “The Sycamore” shows how a $\mathrm{CT^{o7}}$ can be sandwiched between a $\mathrm{cad.^6_4}$ and its resolution to $\begin{smallmatrix}7\\5\\3\end{smallmatrix}$ (Example 6). It appears as though the bass is moving from D to F♯ and back to D, but the F♯ is not related to the functional bass of the passage.

Example 6. Scott Joplin, “The Sycamore,” mm. 1–4. A $\mathit{CT^{o7}}$ that is introduced between the start of the $\mathit{cad.^6_4}$ and its resolution to $\begin{smallmatrix}7\\5\\3\end{smallmatrix}$

In example 7, Chopin uses a $\mathrm{CT^{+6}}$ in m. 8 at the conclusion of a parallel period that is occuring over a tonic pedal. This instance is a common-tone chord that is an incomplete neighbor, because the chord before it in measure 7 is $\mathrm{V^{7}}$ above the tonic pedal. Notice also that Chopin spelled the chord with a C♭ instead of a B♮. Spelling variants do happen with common-tone chords, but the B♮ spelling in this case would have been advantageous because it would have clarified the neighboring function of that note with surrounding Cs in that voice.

Example 7. Frederic Chopin, Etude in F minor, Op. 10, no. 9, mm. 1–9. A $\mathit{CT^{+6}}$ that occurs in the context of a tonic pedal in m. 8.

Assignments
1. Common-Tone Chords (.pdf, .docx.) Asks students to spell common tone chords, realize figured bass, complete 4-part voice leading with Roman numerals, and analyze a musical excerpt. Access audio (excerpt begins at 0:25).