Modulation With Diatonic Common Chords
Dr. B Music Theory


Modulation is a shift to tonal center within movement. It' often used to help establish a form.

What's the difference between modulation and tonicization? Tonicization is a tiny modulation (short time with 2 or 3 chords). Modulation is more and you need cadence.

Key relationships

  1. Harmonically equivalent keys: C# / Db. This is not a modulation as you lesson to the same sound.
  2. Parallel keys: C major / C minor.
  3. Relative keys: C major / A minor.
  4. Closely related keys: no more than 1 accidental, or more or less.

    C%

    G%

  5. Distantly related keys / foreign key relationships. C major 2 more # → D major

Common-Chord Modulation

How to determine possible triads?

Write lead sheet symbols for diatonic triads in:

  1. Current key.
  2. New key.
  3. Analyse triads that occur in both.

Let say current key is Bb major:

Bb ['P1','','I','T'],['M2','m','ii','SD'],['M3','m','iii','d'],['P4','','IV','SD'],['P5','','V','d'],['M6','m','vi','t'],['M7','°','vii°','D']

Let's go to C minor:

C ['P1','m','i','T'],['M2','°','ii°','SD'],['m3','','III','t'],['P4','m','iv','SD'],['P5','','V','d'],['m6','','VI','SD'],['M7','°','vii°','D']

The only two options for common chords are C major and Eb major.

Common-Chord is smooth than using dominant of the new key.

Analyzing Common-Chord Modulation

  1. Find "point of modulation" / "pivot point".
    Chord that is not in the first key or is a tonic 64 in the second key.
  2. Back up one chord and check if this is common-chord.
      | C | G7/F | C/E B°/D  C | C/G G | C  F#°/A  G/B | Am/C |  D7  | G ||
   C:   I   V42    I6  vii°6 I   I64 V   I vii°6/V V6    vi6    V7/V   V
   G:                                    IV vii°6  I6    ii6     V7    I
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