Modulation
A
Key is said to be established when its dominant or dominant seventh chord is followed by the tonic chord. Modulation is the art of passing from one key into another. The crux of modulation is not the sound of the dominant followed by the new key. We can most certainly hear the sudden transition, but a modulation might not have happened. Modulation implies a connection link, a pivot on which the mind readjusts itself to the new key.
‘Pass from X to Y by means of 4 chords’. X -> Pivoting Chord -> Dominant -> Y.
The Pivoting chord has some similarities between the X Key and the Y Key. Keep in mind, Key X must be grounded first. You can’t just use a progression I – Pivot Chord – Dominant Y – Y. The reason being, X Key has not be defined in our minds. One must establish the Key in some fashion.
Major Key: Most usual, most natural modulation is to the dominant. The first part may conclude either with perfect or with an imperfect cadence in the dominant.
It may look something like this:
I – V – V7/V – V :||
Modulation is effected by the leading note of the new key.
C# in the 8th bar makes the V7/V to resolve to the D. Making the Dominant Modulation.
Second usual modulation is to a relative minor key: C major to A minor or E minor: consequently, either into the
submediant (vi) or the median (iii).
Sometimes when modulating to the Submediant, instead of ending in minor key, take the dominant major chord instead.
I – V7/vi - vi – V/vi
Extraordinary Key change. Major Submediant. Notice the pp pianissimo, it reduces the harshness.
When completing the 1st repeat, the composer makes sure it is a smooth transition to the original Key.
And lastly we may modulate by the way of exception. Major key of a Major second below. D Minor to C major. V7/V. The Modulation happens on
A7 to D.