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What Is a Dominant Seventh Chord?

What Is a Dominant Seventh Chord?

A dominant seventh chord is a major triad with a flat seventh on top: 1 – 3 – ♭7 – 5. G7 = G, B, D, F. On charts it's written as just a number — G7, C7, A7 — no "maj," no "m." It's the chord of tension: bluesy, restless, always pointing somewhere.

Why it pulls

Between the chord's third and its flat seventh sits a tritone — the most unstable interval there is. In G7, that's B against F: B strains up toward C, F strains down toward E, and together they collapse into a C major chord. The chord is named "dominant" because it occurs naturally on the dominant — the fifth degree — of every major key, where that collapse lands you on the tonic. V7 → I is the strongest cadence in music.

Two lives: function and flavor

  • Function: in most music, a 7 chord is a signpost — "the chord a fifth below me is coming." Jazz's ii–V–I and the secondary dominants that spice up pop progressions all trade on this.
  • Flavor: the blues ignores the rulebook and uses dominant 7ths as home — I7, IV7, and V7 wall to wall, tension as a resting state. That's the sound dissected in Twelve-Bar Blues Explained.

The shapes and the rest of the seventh family are in Seventh Chords Explained.

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