Related
The idea behind a secondary dominant is simple: if a dominant can point at the tonic, it can point at any other degree too.
In C major the tonic is C. So "the dominant of D" (A–C♯–E) can point at the D minor area — and that A chord is written V/V ("five of five"), a secondary dominant.
The note it introduces (C♯) is not in the C major scale, so a secondary dominant is always an accidental, and always a point of colour change.
The common set
| Symbol | Points at | Chord in C major | New note |
|---|---|---|---|
| V/ii | degree 2 | A major (A–C♯–E) | C♯ |
| V/IV | degree 4 | C major — which is simply I, so no effect | none |
| V/V | degree 5 | D major (D–F♯–A) | F♯ |
| V/vi | degree 6 | E major (E–G♯–B) | G♯ |
Note the second row: V/IV is the same chord as I, so it produces no secondary-dominant effect. To point at the subdominant you need V7/IV (C dominant seventh: C–E–G–B♭), where the B♭ is the new note.
Where it resolves
A secondary dominant's target is the degree it points at, and it normally resolves onto that degree:
V/V → V (D major → G major) V/vi → vi (E major → A minor)
If the target is a minor triad (ii or vi), the raised note in the secondary dominant acts as a temporary leading tone and rises a semitone into the target — exactly the same shape as a real dominant to tonic, simply localised.
How it differs from modulation
Both use the same device — giving a degree its own dominant. The difference is whether it gets confirmed:
| Secondary dominant | Modulation | |
|---|---|---|
| How long the target is emphasised | one or two chords | a whole passage |
| New key signature | does not appear | usually appears |
| Impression | a change of colour | a change of centre |
So the secondary dominant is the commonest means of tonicization (see tonicization).
Diagram: pointing and resolving
Listen: the colour of a secondary dominant
Compare two progressions: I → V → I (entirely diatonic) and I → V/V → V → I (borrowing D's dominant). The brightening in the second is the secondary dominant at work.
Common misconceptions
- "A secondary dominant is a modulation." It is tonicization: the centre is borrowed and returned. The difference is duration and whether a new signature appears.
- "V/IV always brings an accidental." V/IV is the same chord as I and has no effect; V7/IV (with the lowered seventh) is what works.
- "It can point at any degree equally well." In principle yes, but in practice ii, V and vi are the common targets; pointing at vii° or III is weak or easily heard as a modulation.
- "It must resolve." Traditional writing resolves it onto the target; it can also be left unresolved as colour, but then it loses its pointing function.
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Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Sources
- 副属和弦 = 某级的属和弦（V/x 或 V7/x），其升高的音不属于原调音阶，属和声学通则
- 副属和弦造成的短暂中心称为离调，与转调以时长与是否建立新中心区分，为通行表述
Used for fact-checking only; all prose is original.