IV. Diatonic Harmony, Tonicization, and Modulation

Prolongation at Phrase Beginnings using the Leading-tone Chord

John Peterson

Key Takeaways

• Instead of using an inverted $\mathrm{V^7}$ chord to prolong tonic, composers sometimes use $\mathrm{vii^{o7}}$ or its inversions.
• Each inversion if $\mathrm{vii^{o7}}$ can be used in the same way as a particular inversion of $\mathrm{V^7}$. The pairings of $\mathrm{V^7}$ and $\mathrm{vii^{o7}}$ are based on the bass note each chord harmonizes.
• $\mathrm{vii^{o7}}$ can be used anywhere that $\mathrm{V^6_5}$ or $\mathrm{V^6}$ can be used.
• $\mathrm{vii^{o}\begin{smallmatrix}6\\5\end{smallmatrix}}$ or $\mathrm{vii^{o6}}$ can be used in place of $\mathrm{V^4_3}$.
• $\mathrm{vii^{o}\begin{smallmatrix}4\\3\end{smallmatrix}}$ can be used in place of $\mathrm{V^4_2}$.

Overview

Earlier we saw how the tonic can be prolonged using essentially four kinds of progressions, which we categorized according to their basslines (see the summary section for a reminder). In this chapter we consider an alternative way to harmonize those same tonic prolongation basslines using a harmony that can substitute for $\mathrm{V^7}$: the leading-tone chord (meaning the triad or 7th chord built on ti ($\hat{7}$)) (Example 1).

Example 1. Using $\mathit{vii^{o7}}$ vs. $\mathit{V^7}$ in Mozart, “Agnus Dei” from Requiem (0:06–0:20).

Before we address how this substitution works, here are three points we need to emphasize:

1. The leading-tone chord as a triad is always used in first inversion ($\mathrm{vii^{o6}}$). That’s because any other inversion creates a dissonance with the bass that composers tend to avoid.
2. In minor we need to remember to use ti ($\uparrow\hat{7}$), not te ($\downarrow\hat{7}$), to build the leading-tone chord. In other words, remember to raise the leading tone.
3. In major the leading-tone 7th chord’s quality is half diminished if we don’t alter it (e.g. in C major: B-D-F-A). Composers tend to prefer the sound of a fully-diminished 7th chord, though, so we nearly always find that in major keys composers lower the chordal seventh to make the chord fully diminished (e.g. in C major: B-D-F-A♭) (Example 2). You can use both, but $\mathrm{vii^{o7}}$ is much more common than $\mathrm{vii^{o7}}$, and we’ll see why below.

Example 2. Comparing qualities of leading-tone seventh chords.

Substituting the leading-tone chord in place of V(7)

Almost all inversions of $\mathrm{vii^{o7}}$ (plus $\mathrm{vii^{o6}}$) can substitute for an inversion of $\mathrm{V^7}$ (and $\mathrm{V^6}$) according to which note is in the bass (Example 3). What this means is that, for example, $\mathrm{vii^{o7}}$ can be used anywhere that $\mathrm{V^6_5}$ or $\mathrm{V^6}$ can be used. Similarly, $\mathrm{vii^{o}\begin{smallmatrix}6\\5\end{smallmatrix}}$ or $\mathrm{vii^{o6}}$ can be used in place of $\mathrm{V^4_3}$, and $\mathrm{vii^{o}\begin{smallmatrix}4\\3\end{smallmatrix}}$ can be used in place of $\mathrm{V^4_2}$.

Bass note $\mathrm{V}^{7}$ $\mathrm{vii}^{\circ7}$
Ti ($\hat{7}$) $\mathrm{V}\begin{smallmatrix}6\\5\end{smallmatrix}$ $\mathrm{vii}^{\circ7}$
Re ($\hat{2}$) $\mathrm{V}\begin{smallmatrix}4\\3\end{smallmatrix}$ $\mathrm{vii}^{\circ}\begin{smallmatrix}6\\(5)\end{smallmatrix}$
Fa ($\hat{4}$) $\mathrm{V}\begin{smallmatrix}4\\2\end{smallmatrix}$ $\mathrm{vii}^{\circ}\begin{smallmatrix}4\\3\end{smallmatrix}$

Example 3. Substituting $\mathit{vii^{o7}}$ for $\mathit{V^7}$ according to which note is in the bass.

Luckily, there isn’t too much new to learn with respect to part writing. Continue to follow and continue to resolve active notes in the upper voices according to their tendencies. Example 4 reviews these tendencies, and adds the one new note we haven’t seen yet in a dominant-function chord: le/la ($\downarrow\hat{6}$/$\hat{6}$). Example 5 shows tonic prolongations involving $\mathrm{vii^{o7}}$ and its inversions, and it compares each to a corresponding prolongation involving $\mathrm{V^7}$ and its inversions.

Active note Resolution
Ti ($\hat{7}$) Do ($\hat{1}$)
Re ($\hat{2}$) Do ($\hat{1}$)
Fa ($\hat{4}$) Mi ($\hat{3}$)
Le/La ($\downarrow\hat{6}$/$\hat{6}$) Sol ($\hat{5}$)

Example 4. Tendencies of active notes in dominant-function chords.

Example 5. Writing with $\mathit{vii^{o6}}$ and $\mathit{vii^{o7}}$ and its inversions.

viio4/2

You might have noticed that $\mathrm{vii^{o}\begin{smallmatrix}4\\2\end{smallmatrix}}$ doesn’t correspond to an inversion of $\mathrm{V^7}$. That’s because it’s built on le ($\downarrow\hat{6}$), and le ($\downarrow\hat{6}$) isn’t in $\mathrm{V^7}$. $\mathrm{vii^{o}\begin{smallmatrix}4\\2\end{smallmatrix}}$ is a very rare harmony because its bass note, le ($\downarrow\hat{6}$), resolves down to sol ($\hat{5}$) (we saw that le ($\downarrow\hat{6}$) resolves to sol ($\hat{5}$) in Example 4). So far we’ve seen that sol ($\hat{5}$) in the bass typically supports V or $\mathrm{V^7}$, and that’s also the case here: $\mathrm{vii^{o}\begin{smallmatrix}4\\2\end{smallmatrix}}$ goes to $\mathrm{cad.^6_4}$ (Example 6). Again, though, $\mathrm{vii^{o}\begin{smallmatrix}4\\2\end{smallmatrix}}$ is not a very common chord.

Example 6. Using $\mathit{vii^{o}\begin{smallmatrix}4\\2\end{smallmatrix}}$.

Using the leading-tone chord as a half-diminished-seventh chord

$\mathrm{vii^{ø7}}$ presents voice-leading challenges that are not present with $\mathrm{vii^{o7}}$ because it contains a perfect fifth between re ($\hat{2}$) and la ($\hat{6}$). This is perhaps another reason that composers favor $\mathrm{vii^{o7}}$ over $\mathrm{vii^{ø7}}$: with ${ø7}$, we need to watch out for parallel fifths, as in Example 7. An easy way to avoid them is to always make sure that re ($\hat{2}$) is above la ($\hat{6}$) when you use $\mathrm{vii^{ø7}}$ or its inversions. The one time where this advice is impossible is with $\mathrm{vii^{ø}\begin{smallmatrix}6\\5\end{smallmatrix}}$, where re ($\hat{2}$) is in the bass. Although it’s possible to avoid parallels with $\mathrm{vii^{ø}\begin{smallmatrix}6\\5\end{smallmatrix}}$, we’d recommend just using $\mathrm{vii^{o}\begin{smallmatrix}6\\5\end{smallmatrix}}$ instead.

Example 7. Using $\mathit{vii^{ø7}}$ and its inversions.

Assignments
1. Prolongation at Phrase Beginnings using the Leading-tone Chord (.pdf, .docx). Asks students to write from Roman numerals, complete analysis, and realize figured bass.