The dominant seventh
Stack one more third on top of a triad and you have a seventh chord — four notes: root, 3rd, 5th, 7th. The one that matters for everything Classical is the dominant seventh, and it's the engine that drives almost every "we've arrived home" in tonal music.
What it is
Built on the 5th degree — a major triad plus a minor 7th above the root. In G major that's D – F♯ – A – C (sol – ti – re – fa). Written V7.
Why it pulls so hard
The 3rd and the 7th of V7 are ^7 and ^4 of the key — the two most restless degrees — and they sit a tritone apart. The whole chord is built around that tension. When it resolves:
- ^7 → ^1 (F♯ up to G) — the leading tone doing its job
- ^4 → ^3 (C down to B)
Both notes squeeze inward, and the chord collapses onto the tonic triad. That's the strongest resolution in the language.
"The dominant is transportation"
Because V7 → I is such a definite arrival, a piece can move to a brand-new key just by playing that key's V7 first. Toss in the V7 of D major (A–C♯–E–G) and the ear is instantly pointed at D. That's how modulation works, and it's why the circle of fifths is a map of where music can travel.
Try it
Try
Play the V chord of G major without the 7th: D, F♯, A — then resolve to G. Now play it with the 7th: D, F♯, A, C — then resolve to G. The plain V wants to go home; the V7, with that C grinding against the F♯, has to. Feel the difference the one added note makes.
The dominant seventh
- 1
- 2
- 3
- 4
The usual mistake
Playing the leading tone (^7) of a V7 flat, or letting it sag downward. It has one job: climb a half step to the tonic. Give it a touch of extra height and let it rise. The whole chord's pull depends on that note leaning up.