Common-tone Modulation

Common-tone Modulation

While thinking about some of the beautiful compositions of Antonio Carlos Jobim, Gustave and I naturally came around to the topic of modulation — how, when, and why. This led to a discussion of ‘common-tone’ modulation — a technique of interest to Romantic, Impre-
ssionist, and jazz composers — that can be used to expressive effect.

Hello, Gustave;

I hope this finds you well, in great spirits, and enjoying your musical experiences!

Last week, in conjunction with our analysis of Jobim’s Desafinado, we began a discussion about different ways of modulating. I mentioned that the most common method of modulating involves the use of ‘pivot chords’, and you then asked if there are other common ways of creating modulation.

There are a number of other ways of creating modulations — though none is as commonly used as pivot-chord-based modulation. One of these is called “common-tone” modulation — and it’s used in both classical music and jazz. Compared to pivot-chord-based modulation, common-tone modulation is used sparingly. It brings about an abrupt change of key, and composers have often employed it to create dramatic musical — and emotional — effects. Although it really deserves its own complete course of study, I’ll try to give you an idea of how it works, here.

Typically, a common-tone modulation does not use a pivot chord. Its mechanism is — on the surface — very simple: the listener first hears a chord in an established key; then, one note of that chord is sustained (or simply repeated), while all the other notes in that chord change to a chord in another key. The sustained (or repeated) note, however, also belongs to that new chord — quite often with the aid of an enharmonic change (ie, its name is changed — eg, Ab becomes G#).

Aldwell & Schacter's Harmony and Voice-Leading illustrates this with an excerpt from Schumann’s Widmung:

The phrase, in Ab major, ends with a V7sus - I chord progression — and the soprano sings a sustained Ab over the final I. Suddenly, the Ab I chord moves to an unexpected E major chord. The singer repeats the same pitch of Ab — only, now, it is spelled as a G#, which is the third of the E major chord. What follows is a very simple diatonic phrase in the key of E major. A modulation has taken place — a very sudden modulation, between two keys which do not seem to be closely related: Ab major and E major. The mechanism used to create at least some smoothness in the modulation was the soprano's “common tone” — her Ab / G#, which figured very prominently in both the approach to the modulation, and within the modulation itself.

Although the two keys in the Schumann example seem distantly related, they are, in fact, more closely related, via the principle of “mixture”, which is the use of chords and notes of parallel keys (parallel keys share the same tonic, but use different key signatures — eg, C major and C minor). “E major” is simply an enharmonic spelling of “F flat major”; the chord of F flat major is the submediant chord (ie, VI) in the key of Ab minor. So, the Schumann excerpt is actually modulating to a key that is closely related to the key of Ab — but Ab minor, not Ab major. Since most genres and composers freely use parallel keys, this modulation — while certainly more unexpected than a modulation to, say, the dominant key — is not as wild as it seems.

Here is what Harmony and Voice-Leading (in the chapter Chromaticism in Larger Contexts, section New Modulatory Techniques, paragraph 2 — Modulation by common tone) has to say about common-tone modulations:

“Modulations where the main connecting element is a common tone rather than a common chord [ie, pivot chord – ML] are often called common-tone modulations. (If there is a pivot chord . . . this term is not usually applied, even though there might be a prominent common tone.) The common tone will appear in an exposed position, usually in the soprano. Common-tone modu-
lations are particularly effective when the immediate chord progression is from a major triad down a 3rd to another major triad [as was the case in the Schumann excerpt -- ML] . . . Common-tone modulations can create suprising effects.”

In my own thinking, common tone modulations are often associated with what I think of as the use of ‘mode change’. For example, the Schumann example indirectly involves the ‘mode change’ from Ab major to minor — he modulates to VI of Ab minor. Had he simply moved to the key of Ab minor — in various ways — for example, like this:

. . . then this wouldn't have been an example of ‘common-tone modulation’ — even though a common-tone is used here (in the alto) — but simply of ‘mode change’.

In an earlier email, I made a passing reference to the final movement of Ravel's Ma Mere L'Oye, in which there’s a beautiful passage in E phrygian. This passage begins in E phrygian (although the melody temporarily ‘betrays’ the phrygian mode by using an F# instead of an F — I don't know why he did that, but it does sound wonderful), and then modulates — via common-tone modulation — to the key of C# phrygian — that is, down a minor 3rd. Here is a simplified version of it:

As you can see, there is no pivot chord here: the chord Dm doesn't fit in the key of C# phrygian (which has a D major chord, not a D minor). Instead, there is what appears to be a sudden modulation. However, I don't see it as ‘sudden’, but instead, as very subtle. First of all, I regard the modulation technique as being that of common-tone modulation — even though the common tone isn't really sustained, in a direct fashion:  the common tone, to me, is the melody's “E”. If you take a look at the melody's second bar, you will see that it simply plays out one octave of the scale of E aeolian (ie, E phrygian, in which the F natural is temporarily — notice that the accom-
paniment retains the F natural
— replaced by an F#):   EF#GABCDE — the only twist being that Ravel descends an octave from the A on (beauty from simple, but perfect, craft). The phrase begins with a rhythmic repetition of the note E, ascends the E scale, then ends/begins again (a case of melodic “elision” — ie, the E’s at the beginning of the third bar simultaneously end one phrase and begin another) with the same rhythmic repetition on the same E. To my ear, this qualifies as a “common tone” — in the spirit of that term, at the very least, if not in exact detail. While that E ‘stands still’, the rest of the chord — the E minor chord, if we take the broad outline of the phrase, and omit the detail of the Dm minor chord for the moment — moves to new notes: EGB C#EG#. And yet, this isn't only a common-tone modu-
lation, but — to my ears and mind — a beautiful ‘mode change’;  or, to be more precise, a modulation that is the direct result (as was the Schumann example) of mode change. Here's what I mean:

STEP ONE: E phrygian is the relative phrygian of the key of C major
(ie, E phrygian has the same key signature as C major).

STEP TWO: C# phrygian is the relative phrygian of the key of A major.

STEP THREE: C major is the relative major of A minor.

STEP FOUR:  The entire modulation, from a certain perspective, simply
involves a ‘mode change’ from “A minor” to “A major”.

If that's too obscure, try this:

STEP ONE: E phrygian is the relative phrygian of the key of A minor
(it contains the notes of the A minor scale, and is formed
by playing the A minor scale from E to E).

STEP TWO:C# phrygian is the relative phrygian of the key of A major
(it contains the notes of the A major scale, and is formed
by playing the A major scale from C# to C#).

STEP THREE: The modulation from E phrygian to C# phrygian is synony-
mous with a ‘mode change’, from A minor to A major.

Incidentally, notice that the Schumann modulation, which descended by a major 3rd, involved a move from a major scale to its parallel minor (Ab major to Ab minor), and that Ravel's, which descends by a minor 3rd, in-
volves a move from a minor scale to its parallel major (A minor to A major). These seem to be associated with many common-tone modulations, as they appear in Romantic and Impressionist compositions.

The jazz repertoire, as well, contains at least some — and perhaps many — examples of common-tone modulations, as well as modulations that use common-tone and involve mode change.

There are other types of modulation, too, but I think we've already covered
a fair bit of territory, this evening!

If you’re feeling a little disoriented at this point, please don't feel embar-
rassed, or be impatient with yourself! As I mentioned when beginning this lesson, the topic of common-tone modulation really deserves its own com-
plete course of study — one that would follow a similarly full consideration of pivot-chord-based modulation. There’s a great deal to cover, and today’s lesson is just a brief description. (On the other hand, if you aren't feeling disoriented, then give yourself a big pat on the back, because you surely deserve it!)

We will no doubt come back to this subject in the future, as we encounter more examples of common-tone modulation in the jazz, Romantic and Impressionist repertoire.

All the best, Gustave!

Michael Leibson is a composer, music consultant, and music educator, who specializes in jazz and classical harmony. To learn more about him, click here; for information about studying with him, click here; and for copyright information, click here.