Common-tone modulation is the name of a specific way of changing keys in music, and if you want to change keys in a super dramatic and abrupt way, you can use this type of common-tone modulation. What this means is that the last chord in the old key that you’re coming from and the first chord in the new key that you’re going to share a note in common.
And that’s what these two keys have in common is this note. When you change keys in this way, it can be really surprising.
Before explaining further, here’s an example.
Common-Tone Modulation in “Summer of ‘69”
In the “Summer of ‘69” by Bryan Adams, the entire song is in the key of D major, but for the bridge, it moves into F major. Although these two keys do have a complex relationship of F major being the relative major of the parallel minor, these two keys are not considered closely related keys.
This means that moving from one key to a distant key, like with D major to F major, the key change is more noticeable. It draws attention to itself.
The video below is queued up to just before the key change, and the sheet music is below.
Super dramatic, especially with the music video (let’s kick in some doors!).
Let’s talk through the modulation.
At the end of the D major section, we get an A major chord (V in the key of D major), and at the beginning of the F major section, we get an F major chord (I in the new key of F major).
The only note A major and F major have in common is an A. In the notation above, I’ve extended his sung “Oh” on the high A with dotted ties to show that this is the common tone. But you’ll notice that he doesn’t actually hold it out.
It is a common practice to hold out or repeat the shared note during the modulation, like in the abrupt common-tone modulation to the middle section of Chopin’s “Raindrop Prelude” where the A♭ (G♯) gets repeated, first with the V of the old key (A♭ major in the key of D♭ major), then on its own, then with the i chord of the new key (C♯ minor in the new key of C♯ minor).
Despite it being common to hold out or repeat the common tone, it’s not a requirement for this example from “Summer of ‘69” to be classified as a common-tone modulation. That common tone is what bridges the gap between the two keys in this example, so it still counts as a common-tone modulation.
Notating Common-Tone Modulations
The way you can notate common-tone modulations in Roman numeral analyses is simply to write the scale step that the common tone is in each key. In the sheet music above, you’ll notice that at the end of the first line, there’s 5, then a line, and underneath that line is the new key declaration (F: for F major) and the scale degree for the A in that new key: 3.
This signifies that it’s the note itself that is our hinge or pivot for the modulation instead of a chord, and that this isn’t a direct modulation where we just are in a new key without any preparation.
How to Do Your Own Common-Tone Modulations
Remember that common-tone modulations are an abrupt and dramatic way to change keys. These are best for section endings (going to a bridge, like Bryan Adams does here), so be sure that you have an idea of why you want this type of effect in the place you’re putting it over other types of modulation.
- Identify the two keys you’re working with: the old key and the new key
- Write out all of the notes that the two keys have in common
- From that list, pick a note that you’d like to use for your common-tone modulation
- List the chords in both keys that have that note in them
- From those lists of chords, pick one chord per key: one to use as the last chord of the first key and one to use as the first chord of the new key.
Let’s try an example: let’s go from E major to A major. The notes in both keys are:
That means the notes common to both keys are A B C♯ E F♯ and G♯
From there, let’s pick C♯ to use as our common tone. There’s no specific reason why I picked C♯ for this example. You can just pick one!
The chords in E major that have C♯ in them are C♯ minor, A major, and F♯ minor. And A major has C♯ minor, A major, and F♯ minor as well in them.
Now all we have to do is pick on chord from each:
Let’s do C♯ minor and then A major.
First, we end the first key with that C♯ minor chord and to really emphasize that shared note, I’ll repeat it in the upper voice. Then we drop out the harmony and have just the upper voice repeating that C♯. Then, we end our modulation by bringing in new harmony with the A major triad.
Of course, it sounds more abrupt with the context of being in a key for a long time and then suddenly switching and redefining the role of that C♯ from being 6 to being 3.
To really lock in the new key, follow up the common-tone modulation with a strong cadence in the new key, which means you’ll want to have a V – I in the new key shortly after.
Learn More About Common-Tone Modulation and Other Chromatic Harmony Concepts
To learn more about common-tone modulations, other ways to change keys, and other ways to borrow chords from other keys, check out the Chromatic Harmony: Advanced Chord Progressions ebook and Chord Progressions: Cadences to Key Changes course!