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Secondary dominants
Tonicising any chord: V of V and its relatives.
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Stop 1 of 6
Tonicising any chord: V of V and its relatives.
Welcome to the observatory. From up here a key stops being a closed box of seven chords and becomes a sky full of gravitational pulls. The first one you will study is the most widely used in jazz, pop, bolero and classical music: the , a chord that turns any chord of the key, for a moment, into a small tonic.
Start with your ears. These two progressions in C major differ in one chord only, the second bar. Listen to them back to back, with your eyes closed if you can:
In version B the second chord no longer "rests": it asks to go to Dm. When it gets there, Dm sounds for a moment like home. Compare the two chords on their own:
The only difference is one note: C becomes C♯. That C♯ sits a half step below D, the root of Dm, and works as a borrowed leading tone. Hear it resolve:
When you make a chord sound like a destination by giving it its own dominant, you are tonicising it. is a momentary zoom: for a bar or two the ear treats Dm as the centre, but the key of C is still in charge.
The chord symbol says so with a slash: V/ii reads "five of two", meaning "the chord that would be V if ii were the tonic". To find it:
In C major you get this family:
| Target | Secondary dominant | Notes | Note that changes |
|---|---|---|---|
| ii (Dm) | V/ii = A7 | A C# E G | C → C♯ |
| iii (Em) | V/iii = B7 | B D# F# A | D → D♯, F → F♯ |
| IV (F) | V/IV = C7 | C E G Bb | B → B♭ |
| V (G) | V/V = D7 | D F# A C | F → F♯ |
| vi (Am) | V/vi = E7 | E G# B D | G → G♯ |
vii° is missing: a diminished chord does not sound stable, so in practice it is not tonicised. And V/I is simply G7, the usual dominant.
The most common secondary dominant is V/V, which classical theory calls the double dominant. It prepares the arrival of the main dominant and stretches the cadence. Hear how D7 makes G7 sound even more inevitable:
What makes it work is . Play only the (third and seventh): from D7 to G7 each voice falls a half step, and from G7 to Cmaj7 the seventh falls again.
If each dominant resolves to another dominant, you get a chain that travels round the circle of fifths: E7 → A7 → D7 → G7 → C. Technically these dominants do not resolve to their diatonic target (A7 does not go to Am but to another dominant), which is why they are sometimes called extended dominants. III7–VI7–II7–V7 sequences are typical of the bridges of many swing-era jazz tunes. The thirds and sevenths of the chain keep falling by half steps: it is the same voice leading you just played, repeated.
To improvise or write melodies over a secondary dominant, think of its with a very practical rule: use the notes of the key and change only the ones the chord alters. The result depends on whether the target is major or minor:
| Chord | Resolves to | Scale | Notes |
|---|---|---|---|
| D7 (V/V) | G major | D E F# G A B C | |
| C7 (V/IV) | F major | Mixolydian | C D E F G A Bb |
| A7 (V/ii) | Dm minor | Mixolydian b9 b13 (Phrygian dominant) | A Bb C# D E F G |
| E7 (V/vi) | Am minor | Phrygian dominant | E F G# A B C D |
| B7 (V/iii) | Em minor | Phrygian dominant | B C D# E F# G A |
When the target is minor, the dominant's ♭9 and ♭13 match the ♭3 and ♭6 of the minor key it is heading for. That's why they sound "at home". It is the scale you met as the fifth mode of :
String 6, Fret 5: A2 · 1 · Root
This line runs through the scale over A7 and resolves to the notes of Dm. Watch the last note of the first bar: C♯ rises to D.
Goal: Play the thirds and sevenths of the whole progression without stopping at 80 BPM, with every leading tone resolving by half step.
Goal: Improvise eight bars over C – A7 – Dm – G7, playing C# in every A7 bar and resolving it to D.
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