Triads are often extended with some form of the seventh to form a seventh chord. When a chord is referred to as simply a seventh chord, usually the dominant seventh is meant, which is a major triad with a minor seventh, for instance, C-E-G-B♭. It is called the dominant seventh because the V chord, or "dominant chord" in the Latin naming system, is the only chord in the major scale that can naturally contain a minor seventh. Because all sevenths are dissonant intervals, any seventh chord is dissonant, in other words, a seventh chord is more tense than a major or minor chord. However, a few styles of music, such as jazz, make heavy use of seventh chords and may treat them as rather consonant. A variety of sevenths may be added to a variety of triads, resulting in many different types of seventh chords, as described below. Of the eight possible constructions of seventh chords using major and minor thirds, seven are commonly found in western music (in addition to the synthetic "altered" seventh). They are built as indicated below: |
| Names | Other Names | Voices |
|---|---|---|
| Major Seventh | maj7, M7, Δ7, ⑦ | root, major third, perfect fifth, major seventh |
| Minor Seventh | m7, -7 | root, minor third, perfect fifth, minor seventh |
| Dominant Seventh | Major/Minor Seventh, 7 | root, major third, perfect fifth, minor seventh |
| Half Diminished | m7♭5, -7♭5, ø | root, minor third, diminished fifth, minor seventh |
| Diminished Seventh | °7 | root, minor third, diminished fifth (tritone), diminished seventh (enharmonic major sixth) |
| Minor Major Seventh | mM7, mmaj7, mΔ7, -Δ7, m⑦ | root, minor third, perfect fifth, major seventh |
| Altered Chord | 7alt | root, third, diminished fifth (or augmented fifth), flat seventh, flat ninth (or sharp ninth) |
| Augmented Major Seventh | maj7(#5), maj+7, Δ+7 | root, major 3rd, augmented 5th, major seventh |
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