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Seventh chords add a seventh degree above the root, creating four-note chords. The dominant seventh (V7) is the most common—it combines the dominant chord's tendency to resolve upward with the tritone (formed by the third and seventh) that demands resolution. Other seventh chords include major seventh, minor seventh, and half-diminished seventh, each with distinct colors and functions.
You already know how to build diatonic chords — triads constructed by stacking thirds within a key — and you've studied interval quality by counting semitones. A seventh chord extends this stacking one step further: take a triad and add one more third on top, creating a four-note chord whose highest note is a seventh above the root. Each diatonic scale position produces a characteristic seventh chord type depending on the quality of the triad and the quality of the added seventh interval.
The most important is the dominant seventh (V7). In C major, V7 is G-B-D-F. The triad G-B-D was already the dominant chord with its leading-tone energy; adding the minor seventh F introduces something new — a tritone between B and F. You know from interval quality that the tritone (three whole steps) is the most dissonant interval in tonal music, the one medieval theorists called *diabolus in musica*. In G7, B wants to resolve *up* by half step to C (it's the leading tone), and F wants to resolve *down* by half step to E (it's the seventh, pulling toward the third of the tonic chord). These two half-step resolutions squeeze inward simultaneously, creating irresistible harmonic momentum toward the tonic. This is why V7-I is the strongest, most conclusive harmonic motion in tonal music.
The other seventh chord types have different characters. A major seventh chord (e.g., Cmaj7: C-E-G-B) adds a major seventh — a wide, lush interval that creates a dreamy, sophisticated sound. The major seventh doesn't create the same urgent resolution pull as the tritone; instead it adds color and warmth. This is why major seventh chords are common in jazz and ballads but rare in classical functional harmony where clear resolution is the priority. A minor seventh chord (e.g., Dm7: D-F-A-C) adds a minor seventh to a minor triad, producing a cooler, more understated sound — common on the ii chord (in C major: D-F-A-C) where it adds smooth voice leading into the V chord.
Understanding seventh chords means understanding the difference between color and function. The V7 chord is primarily *functional* — its internal tritone drives harmonic motion. Major seventh chords are primarily *coloristic* — they extend a sound without creating urgent tension. In analysis, you need to distinguish these: a Imaj7 at the end of a piece is a final resting place with added richness; a V7 is an unstable pivot demanding resolution. As you encounter harmonic progressions, notice not just what the chord is, but whether the added seventh is creating tension that needs releasing or simply extending the color of a stable moment.
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