Just as we can tonicize non-tonic chords by borrowing their dominant chords, we can also tonicize non-tonic chords by borrowing the leading-tone chord (viio) from that same key. A secondary leading-tone chord follows all of the same voice-leading rules as if it were written in the borrowed key.
There are two different ways to explore secondary leading-tone chords(viio/x)–through functional substitution as a dominant chord or through functional substitution as a pre-dominant chord.
In Unit 11b, we introduced the idea of functional substitution as a way to explore how chords with similar functions are related. To better understand the voice-leading of viio chords, I asked you to think of them as V7 chords without the root. This explains why viio breaks many of standard part-writing doubling conventions.
First, harmonize the following example as written, and then turn the ii7 chord into a V7/V by adding the appropriate accidental.
In doing this, you have created a well-voiced secondary dominant seventh chord, V7/V that should look something like this:
To turn this into a secondary leading-tone chord, you need to replace the root–in this case, the pitch D–with a note from viio/V. While this is a simple statement, I hope that you remember our discussions of the difficulties in voicing a viio triad. You do not want to double the tendency tones, because one of them will need to resolve incorrectly to avoid objectionable parallels with each other. And because there are so many tendency tones–the root, fifth, and seventh of any viio7 are all tendency tones–you need to be careful of where each voice is placed to avoid parallelisms, poor resolutions, and spacing errors.
As you work on revoicing your V7/V, take note of which pitch you choose to double. What other changes are necessary to avoid poor resolutions? You may choose to use any inversion for your viio/V chord, so try re-voicing using the following voicing:
If you tried to create your viio/V based on the V7/V voicing from above, it is likely that you immediately ran into issues in trying to eliminate the D from the bass. Substituting an A in the same octave creates parallel octaves against the tenor. If we do not alter our upper voices from the completed V7/V example, substituting an F-sharp in the bass creates parallel octaves against the alto. You could frustrate the leading tone in the alto as a workaround, but the fact remains: viio triads are difficult to use as a dominant function with good voice-leading, and there is no straightforward answer to the above exercise that does not require manipulating the chords around the secondary leading-tone chord. For example, the following progression solves this through creating a leap in the tenor voice and tripling the tonic on the final chord.
It is easier, but still restrictive, to use a viio as a seventh chord. In the following example, try to using a viiø7/V using the provided bass line. You may use either a fully diminished or half-diminished seventh chord in this example.
The most obvious solution is written below, and it feels like the part-writing takes care of itself. In this usage however, the viiø7/V creates parallel fifths between the alto and tenor voices.
Instead, you must figure out a way to get the chordal third above chordal seventh in your voicing. This is restrictive in your spacing, but it does solve the objectionable parallels:
Remember that because a secondary leading tone chord (e.g. viio/V) or viiø7/V) is a functional substitution for a secondary dominant chord (e.g. V/V) chord, the root and fifth of the viiø7/V are acting as if they were the third and seventh of the V6/5/V chord. You can see this when you voice the two chords side-by-side.
It is also helpful to approach secondary leading-tone chords by exploring the dual nature of their function. To this point, we have focused on their role as dominant function chords in a second key. For example, we have shown repeatedly that a V7/V functions as the V chord in the key of V. This explains their voice-leading, but it does not address their actual function within the progression as a whole in the home key–the key of I. In the home key, the V7/V takes the place of a pre-dominant chord, most often replacing a ii chord, but like ii and IV, it can move laterally between them. (e.g. A ii7 can move to a V7/V and then resolve to V.)
This can be applied to viio7/x as well. Notice that the roots of both dominant function chords–V and viio–and the roots of pre-dominant chords–ii and IV–are separated by the interval of a third. If we add this observation to the idea that a V/V chord is a functional substitution for a ii chord, it reasons that a viio chord is therefore a functional substitution for a IV chord. They share a function and have a root that is a third higher than their more commonly used counterpart.
You can demonstrate this by harmonizing the following diatonic progression. Once you have a harmonization with good voice-leading, alter the IV6 chord to become the viiø7 chord from the key of the chord you will be tonicizing–in this case, the viiø7 from G major. What note(s) do you have to alter to achieve this? How do these notes relate to a V7/V? Did you have to re-voice this to accommodate the alterations?
After having done this, do you feel that viio is more closely related to ii7 or IV? Why?