Tonicization or modulation?
A secondary dominant tonicizes for a moment. We speak of modulation when the new key is confirmed by a cadence and lasts long enough to become the new home.
The techniques
- Pivot chord: a chord common to the two keys acts as a hinge. From C to G: Am is vi in C and ii in G. C – F – Am – D7 – G.
- Direct (phrase) modulation: the new section starts in the new key without preparation. Verse in C, chorus in Eb.
- Truck driver modulation: the last chorus raised by a half step or a whole step (C → Db). Often prepared by the new dominant: G – Ab7 – Db.
- Common tone: a held note connects two distant keys. G held: C major → Eb major (G is the third of Eb).
- Chromatic: a voice moves by semitone and reinterprets the chord: C – C7 – F (or C – E7 – Am).
- Enharmonic: with diminished sevenths (G#°7 = B°7 = D°7 = F°7) or with the German sixth reinterpreted as a dominant seventh (Ab7 in C = G# Ger6 toward C#).
- Sequential: a model repeated by whole steps leads into a new key.
Closely and distantly related keys
From C: close are G, F, Am, Em, Dm; more distant Eb, Ab, E, A (chromatic mediants, cinematic sound).
Effect on the audience
Going up a key raises the energy; going down creates an “intimate” effect. In modern pop songs modulation is rarer: energy is preferably obtained through arrangement and vocal register.
Real example
“Love On Top” by Beyoncé (2011) in the finale goes up in key by semitone several times in a row: the truck driver modulation taken to the extreme. “Man in the Mirror” by Michael Jackson (1987) goes up a half step for the last chorus.