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The dominant seventh is the most famous seventh chord: a major triad plus a minor seventh.
C dominant seventh = C–E–G–B♭ (major triad C–E–G, plus the minor seventh B♭)
The "dominant" in the name refers to its usual home, degree 5 of the key. It is the strongest propulsive force in tonal music, and the reason is hidden where you would not first look.
The tritone inside
Spread the four notes out and one pair matters most:
The third (E) and the seventh (B♭) are six semitones apart — a tritone.
That is the engine. The two notes of the tritone pull in opposite directions:
| Note | Tendency |
|---|---|
| the third, E | rises a semitone to the tonic, F |
| the seventh, B♭ | falls a semitone to A |
One rises, one falls, and both resolve at once — the cleanest closing gesture there is. The tritone is among the least settled intervals (see augmented and diminished), and the dominant seventh packs it into a single chord — turning instability into a planned, harmonically usable tool.
Two constructions, major and minor
| Context | Content | Note |
|---|---|---|
| V7 in major | major triad + minor seventh, straight from the scale | no accidental needed |
| V7 in minor | the seventh degree must be raised | natural minor's degree 5 is a minor seventh chord; [[concept:harmonic-minor |
The second line answers a long-standing puzzle: why do minor-key works keep sharpening the seventh? Without it there is no dominant seventh — and therefore no harmony capable of driving a close.
Why it also enables modulation
The dominant seventh has a further use: it contains a tritone, and a tritone is asymmetrical. The same chord can be reinterpreted as the dominant seventh of another key — one of the commonest means of modulation, and the harmonic basis that lets the circle of fifths keep turning.
Diagram: the third and seventh resolving in opposite directions
Listen: the dominant seventh
Hear the block first (it clearly wants to move), then press Arpeggio to hear the distance between third and seventh.
Common misconceptions
- "A dominant seventh is simply the chord on degree 5." What matters more is its structure (major triad plus minor seventh) and the tritone that follows. Its position gave it the name, not its definition.
- "A minor key's dominant seventh comes from natural minor." Natural minor's degree 5 is a minor seventh chord. Getting a dominant seventh requires raising the seventh.
- "A dominant seventh must resolve to the tonic." In traditional harmony almost always; in jazz and pop it often acts as a stable colour or heads elsewhere.
- "Dominant and major sevenths differ by one note, so they sound similar." The difference is a semitone, and the tension differs enormously — a minor seventh is soft, a major seventh sharp.
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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
- 属七和弦 = 大三和弦 + 小七度，根音到七音为小七度；三音与七音之间构成三全音，属和声学通则
- 属七和弦在大小调中的构成差异（小调须升第 7 级）为通行和声学表述
Used for fact-checking only; all prose is original.