Secondary dominants
Music theory · Tonal harmony · Level 5 · 15 min
The dominant is so effective at highlighting the tonic that you can apply it to any major or minor chord in the key. A secondary dominant is the dominant chord (V or V7) of a degree other than the tonic. It is written V/x (“five of x”).
| Symbol | In C major | Telltale accidental | Resolves to |
|---|---|---|---|
| V7/ii | A7 (A C♯ E G) | C♯ | Dm |
| V7/iii | B7 (B D♯ F♯ A) | D♯, F♯ | Em |
| V7/IV | C7 (C E G B♭) | B♭ | F |
| V7/V | D7 (D F♯ A C) | F♯ | G |
| V7/vi | E7 (E G♯ B D) | G♯ | Am |
There's no V/vii°: a diminished chord can't act as a tonic, even briefly.
Tonicisation
For a moment, the target chord becomes a little tonic: this is called tonicisation. It isn't a modulation — we don't really leave the key — but a spotlight. The accidental introduced is almost always the leading tone of the target chord (F♯ for G, G♯ for A…).
M:4/4
L:1/4
%%staves {RH LH}
V:RH clef=treble
V:LH clef=bass
K:C
[V:RH] "C"[EGc]2 "E7"[E^Gd]2 | "Am"[EAc]2 "D7"[^FAc]2 | "G7"[FGB]2 "C"[EGc]2 |]
[V:LH] "_I"C,2 "_V7/vi"E,2 | "_vi"A,,2 "_V7/V"D,2 | "_V7"G,,2 "_I"C,2 |]
Listen to how each seventh chord “pulls” toward the next: G♯ rises to A, F♯ rises to G, and each seventh falls (D → C, C → B).
Chains of dominants
E7 – A7 – D7 – G7 – C: each chord is the dominant of the next. This chain, typical of ragtime, traditional jazz and barbershop harmony, travels round the circle of fifths. Between two consecutive dominant sevenths, the seventh falls a semitone to become the next chord's third, and the third falls a semitone to become the next seventh: two very elegant descending chromatic lines.
Secondary leading-tone chords
Likewise you can use vii°7/x, the diminished seventh built on the leading tone of the target chord. Example: F♯°7 → G (vii°7/V). Very common in Bach and Beethoven.