Triads are the primary colours. Sevenths and extensions are everything else in the paint box. They are the sound of soul, jazz, neo-soul, R&B, house and lo-fi - and used carefully, they make a simple progression sound expensive.
Seventh chords
Add a fourth note, a third above the fifth, and you have a seventh chord. Four types cover almost everything:
- Major seventh (maj7) - major triad plus a major seventh. Cmaj7 = C-E-G-B. Dreamy, lush, unresolved.
- Minor seventh (m7) - minor triad plus a minor seventh. Am7 = A-C-E-G. Soft, warm, smooth.
- Dominant seventh (7) - major triad plus a minor seventh. G7 = G-B-D-F. Bluesy, tense - it wants to move. This is the chord built on the fifth note of a major key, and its tension is what drives V back to I.
- Half-diminished (m7b5) - diminished triad plus a minor seventh. Bm7b5 = B-D-F-A. Melancholy, unstable - the ii chord of minor-key jazz.
The diatonic seventh chords of C major: Cmaj7, Dm7, Em7, Fmaj7, G7, Am7, Bm7b5.
Extensions
Keep stacking thirds above the seventh and you reach the extensions:
- 9th - the second note of the scale, an octave up. Cmaj9 adds D. Adds openness and shimmer.
- 11th - the fourth, an octave up. Most effective on minor chords: Am11 is the floating sound of a great deal of house and neo-soul.
- 13th - the sixth, an octave up. Common on dominant chords in jazz and funk.
You rarely play every note of an extended chord. On a keyboard, players drop the fifth (it adds little) and often the root (the bass is already playing it). Voiced well, a four-note chord can imply a thirteenth.
Suspended and added chords
- sus2 - the third replaced by the second. Csus2 = C-D-G. Open, neutral, neither major nor minor.
- sus4 - the third replaced by the fourth. Csus4 = C-F-G. Tension that wants to resolve down to the third.
- add9 - a triad plus the ninth, with no seventh. Cadd9 = C-E-G-D. Bright and modern; huge in acoustic pop.
- 6 chords - a triad plus the sixth. C6 = C-E-G-A. Vintage, sweet.
Inversions
An inversion puts a note other than the root in the bass.
- Root position - C-E-G, C in the bass.
- First inversion - E in the bass (written C/E). Lighter, less settled.
- Second inversion - G in the bass (C/G). Unstable; often used in passing.
Inversions let a bassline move smoothly by step while the chords change above it: C - C/B - Am - Am/G - F is a descending bassline under an ordinary progression, and it sounds far more sophisticated than the root-position version.
Chord variations
One of the most useful exercises in composition: make a progression using variations on a single chord. Hold C as the root and move through C, Cmaj7, C7, C6, Csus4, Cadd9. The bass never moves, but the colour changes constantly - enough to carry a verse.
This works especially well in electronic music, where a long section on one root note keeps the low end steady while the harmony above it evolves.
Voicing and voice leading
How you arrange the notes of a chord - its voicing - matters as much as which chord it is.
- Close voicings keep notes within an octave. Dense, keyboard-like.
- Open voicings spread them out. Wider, more orchestral.
- Voice leading is moving from chord to chord with as little movement as possible in each note. Cmaj7 to Am7 shares three notes - only the top note moves. Smooth voice leading is what makes extended chords sound effortless rather than like a series of blocks.
Do this now
- Build the seven diatonic seventh chords of C major and play them in order.
- Rewrite the I-V-vi-IV progression in C with sevenths: Cmaj7-G7-Am7-Fmaj7. Then try Cmaj9-G6-Am11-Fmaj7.
- Write a four-bar section on a C root that moves through at least four chord variations.
- Revoice your progression so that no note moves by more than two semitones between chords.