Chord Construction
Seventh chords — adding the 7th
Stack one more third on a triad and you get a 7th chord. The basis of jazz, soul, and modern pop harmony.
What a 7th chord is
A seventh chord is a triad with one more third stacked on top. The new note is some kind of 7th (major, minor, or diminished) from the root.
Five common 7th-chord types:
| Name | Spelling | Intervals | Example (C root) |
|---|---|---|---|
| Major 7th | maj7 / Δ7 | 1 3 5 7 | C E G B |
| Minor 7th | m7 | 1 ♭3 5 ♭7 | C E♭ G B♭ |
| Dominant 7th | 7 / dom7 | 1 3 5 ♭7 | C E G B♭ |
| Minor 7♭5 (half-dim) | m7♭5 / ø | 1 ♭3 ♭5 ♭7 | C E♭ G♭ B♭ |
| Diminished 7th | dim7 / °7 | 1 ♭3 ♭5 ♭♭7 | C E♭ G♭ B♭♭ |
The dominant 7th is the most important one in tonal music — its mix of a major triad with a minor 7th creates the strongest “wants to resolve” feel in Western harmony.
The sound of each
- maj7: dreamy, lush, slightly tense. Sounds like jazz or movie-soundtrack peace.
- m7: smooth, mellow. The default sophisticated minor chord.
- dom7: bluesy, unresolved, urgent. The pivot point of nearly every blues, jazz, and many pop songs.
- m7♭5: dark and uncertain. Used in minor key ii-V’s and in moments of moody transition.
- dim7: extremely tense, all stacked minor thirds. A passing chord used to slide between two other chords.
Building them on the guitar
The “root on 6th string” voicings for an A root:
| Chord | 6 | 5 | 4 | 3 | 2 | 1 |
|---|---|---|---|---|---|---|
| Amaj7 | 5 | 7 | 6 | 6 | – | – |
| Am7 | 5 | 7 | 5 | 5 | – | – |
| A7 | 5 | 7 | 5 | 6 | – | – |
| Am7♭5 | 5 | 6 | 5 | 5 | – | – |
(Numbers are fret numbers; – means muted or skipped. Memorise these four shapes — they’ll get you through 80% of jazz and modern pop.)
Why the 7th changes everything
The third of a triad gives it major/minor character. The seventh adds tension. A C chord and a C7 sound completely different — and you can swap a C for a C7 in many progressions to add color.
This is the harmonic move that opens up jazz: every “simple” triad gets replaced by some flavor of 7th chord, then 9th, 11th, 13th. Same harmony, more colour.
Try this
Play C major and Cmaj7 back to back. Just adding the B note (the major 7) on top transforms the chord from “everyday major” to “movie soundtrack”.
Now play G major and G7. Adding the F note (the ♭7) transforms it from “vanilla major” to “you’d better resolve me — probably to C”.
This is the entire universe of functional harmony in two examples.