Definition
Modulation by common chord (or diatonic, pivot chord modulation) moves from one key to another through a chord that belongs to both. This chord, called the pivot, is first heard with the function of the old key and then reinterpreted with that of the new one. It is the smoothest and most natural way to modulate, and it is used above all toward closely related keys.
Closely related keys
Two keys are closely related if their key signatures differ by at most one accidental. For C major:
- G major (dominant) and F major (subdominant);
- A minor (relative);
- E minor and D minor (relatives of G and F).
These are the keys of the major and minor triads of the C scale (ii, iii, IV, V, vi): that is why they share many chords.
The common chords
| From C major to | Common chords (function in C = function in the new key) |
|---|---|
| G major | C (I = IV), Em (iii = vi), G (V = I), Am (vi = ii) |
| F major | C (I = V), Dm (ii = vi), F (IV = I), Am (vi = iii) |
| A minor | Dm (ii = iv), F (IV = VI), C (I = III), Am (vi = i) |
| E minor | C (I = VI), Am (vi = iv), Em (iii = i), G (V = III) |
The procedure in three phases
- Establish the starting key with a clear progression.
- Use the pivot chord, preferably with a predominant function in the new key (ii or IV), so that it leads naturally to the new dominant.
- Introduce the dominant of the new key (with the altered note that characterizes it) and confirm with a perfect cadence.
Examples of progressions
- C → G: C – Am (vi = ii) – D7 – G. The appearance of the F# in the D7 makes the change clear.
- C → A minor: C – F – Dm (ii = iv) – E7 – Am.
- C → F: C – Dm (ii = vi) – Bb – C7 – F.
- C → E minor: C – Am (vi = iv) – B7 – Em.
Practical rules
- The best pivot is a chord that has a function of predominant in the new key.
- Avoid the tonic of the new key as a pivot: if the arrival chord is already the new tonic, the modulation arrives too early and without preparation.
- A modulation is considered complete only after a cadence in the new key; otherwise it is a tonicization.
- In analysis, write the pivot with two stacked Roman numerals (for example vi in C / ii in G).
Common mistakes
- Introducing the new dominant without preparation and calling it a common-chord modulation: it is a direct modulation.
- Choosing a pivot that already contains the altered note of the new key (for example Bm in C→G: in C it does not exist as a diatonic triad).
- Not confirming the new key with a cadence.
Examples from the repertoire
- Bach, Invention no. 1 in C major: after the exposition the music moves to G major with a cadence, then to A minor, always through shared chords.
- Classical sonata expositions (Mozart, Haydn): the bridge modulates to the dominant, often using the vi or the ii as a pivot.
- Baroque binary form: the first part almost always modulates to the dominant (in major) or the relative (in minor) with a common chord.
How to use it in composition
- For a bridge or a bridge section that goes “elsewhere” without jolts, choose a closely related key and a pivot with predominant function.
- In pop, modulation by common chord is more discreet than direct modulation: it is used when you want to change color without a showy effect.
- To get back home, apply the same procedure in reverse.
Exercise
- Write an 8-bar phrase that starts in D major and cadences in A major using a pivot.
- Modulate from F major to D minor and then return to F.
- Analyze the exposition of a Mozart sonata and find the pivot chord.
Connections
Modulation techniques; Tonicization; Circle of fifths and closely related keys; Chromatic and direct modulation; Enharmonic modulation; Binary form; Sonata form.