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A seventh chord extends a triad by adding a fourth note — a seventh above the root. The five common types are: major seventh (Maj7), dominant seventh (7), minor seventh (m7), half-diminished seventh (ø7), and fully diminished seventh (°7). The dominant seventh chord (major triad + minor seventh) is especially important because its tritone interval creates strong harmonic tension that resolves to the tonic. Seventh chords are ubiquitous in jazz, blues, classical, and pop music.
Build each seventh chord type above C and compare the top interval (the seventh) in each case. Learn the five types in the context of the major scale diatonic seventh chords. Play V7–I progressions to feel the resolution of the tritone.
You already know how to build triads — stacking thirds above a root to get a three-note chord. A seventh chord is simply the next step: add one more third on top of the triad, and you have a four-note chord. The added note falls a seventh above the root, which is where these chords get their name.
The five common seventh chord types differ in which triad they start with and which seventh they place on top. The major seventh (Maj7) stacks a major seventh on a major triad — the top note is almost, but not quite, an octave above the root, creating a lush, stable sound. The dominant seventh (7) also uses a major triad but lowers the top note by a half-step to a minor seventh, introducing tension. The minor seventh (m7) pairs a minor triad with a minor seventh — softer and more melancholic. The half-diminished (ø7) uses a diminished triad with a minor seventh, and the fully diminished (°7) uses a diminished triad with a diminished seventh — the most harmonically dense of the five.
The dominant seventh is the most important chord in tonal music. Because it contains a tritone — the interval between its third and seventh — it generates the strongest harmonic pull you will encounter. In G7 (in the key of C major), the notes B and F are a tritone apart. B naturally rises a half-step to C; F naturally falls a half-step to E. Playing a V7–I progression and listening to this resolution is one of the most revealing ear-training exercises in music theory. Once you can hear this pull, you will notice it everywhere — in Bach, in blues, in pop music.
As you continue into diatonic harmony, you will discover that each degree of the major scale generates its own seventh chord type when harmonized in thirds. These seven diatonic seventh chords — one of each type — form the harmonic vocabulary of jazz, classical, and contemporary music. Recognizing the dominant seventh by its tension and the major seventh by its stability will transform how you listen to and analyze chord progressions.
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