The A dominant seventh chord is built by stacking a major third, a perfect fifth, and a minor seventh above the root. The interval between the major third (C♯) and the minor seventh (G) creates a tritone—the most dissonant interval in tonal music—which generates the powerful pull toward resolution that defines dominant function in functional harmony.
Resolution and Voice Leading
In traditional harmony, the A7 chord resolves most naturally to the chord a perfect fourth above its root. The tritone within the chord resolves by voice leading—the major third moves up by a semitone and the minor seventh moves down by a semitone, creating a satisfying resolution. This V7–I motion is the strongest harmonic progression in Western music.
Beyond Classical Harmony
While classical music uses dominant seventh chords primarily for resolution, blues and jazz treat them as stable sonorities in their own right. A twelve-bar blues progression uses dominant seventh chords on every degree (I7–IV7–V7), embracing the tension rather than resolving it. In jazz, the A7 chord serves as a launching point for improvisation and can be enriched with extensions like ninths, elevenths, and thirteenths.