Stop 3 of 6
Seventh chords
maj7, m7, 7 and m7♭5: four-part harmony.
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Up to now almost all your harmony has had three notes. Add a fourth note, the seventh, and chords change colour: pop turns into soul, rock into jazz, a nursery tune into bossa nova. In this stop you build the five basic , learn to tell them apart by ear and play them as open and barre shapes. By the end you will harmonise the whole major scale in four voices.
Ears first. Listen to the C triad, then the same triad with one more note on top. That note is the seventh: the third we stack on top of the fifth.
The second sounds soft and bright, almost floating. The third sounds restless, as if it wanted to go somewhere. The difference is a single note: B versus B♭, a half step.
This is how the five seventh chords are built, all on C so you can compare:
| Chord | Formula | Notes on C | Triad + seventh | Character |
|---|---|---|---|---|
| Cmaj7 | 1 3 5 7 | C E G B | major + major 7 | bright, dreamy |
| C7 | 1 3 5 ♭7 | C E G B♭ | major + minor 7 | tense, wants to resolve |
| Cm7 | 1 ♭3 5 ♭7 | C E♭ G B♭ | minor + minor 7 | warm, relaxed |
| Cm7♭5 | 1 ♭3 ♭5 ♭7 | C E♭ G♭ B♭ | diminished + minor 7 | uneasy, soft |
| Cdim7 | 1 ♭3 ♭5 𝄫7 | C E♭ G♭ B𝄫 | diminished + diminished 7 | dramatic, floating |
Listen to all five in a row, from the most stable to the most tense:
The names in detail:
Every seventh chord is a stack of thirds. Look at the "DNA" of each one, bottom to top: maj7 = M3 + m3 + M3; 7 = M3 + m3 + m3; m7 = m3 + M3 + m3; m7♭5 = m3 + m3 + M3; dim7 = m3 + m3 + m3. The dim7 is the only one built from equal minor thirds: that is why it splits the octave into four exact parts and its shape repeats every three frets.
Many open seventh chords are chords you already know with one finger fewer or one more. Play them and listen to the colour:
With the diagrams labelled by degree, find the seventh of each chord (7 or ♭7). Often it is an open string or a note that "replaces" a doubled root.
To play seventh chords in any key you need two movable families, derived from the and the . First, with the root on the sixth string (here on G, fret 3):
And with the root on the fifth string (on C, fret 3):
Notice how a single finger changes between neighbouring shapes: from maj7 to 7 the seventh drops a fret; from 7 to m7 the third drops; from m7 to m7♭5 the fifth drops. Each chord is a small adjustment of the previous one.
Cdim7 has a curious property: since it is made of four equal minor thirds, any of its notes can be the root. Cdim7, E♭dim7, G♭dim7 and Adim7 contain the same four notes. On the guitar that means the same shape, moved three frets, is still the same chord with another note in the bass:
That is why guitarists use it as a passing chord: it slides three frets at a time to join two chords or to build suspense. It does not belong to the major scale, but you will meet it often in The Harmony Observatory.
Each seventh chord has its habitat. maj7 is the sound of bossa nova, smooth soul and many pop ballads: a chord of rest with a touch of nostalgia. m7 is the foundation of funk and R&B, where a single minor seventh chord can carry a whole song. 7 is the heart of blues and rock and roll, and in jazz it is the chord that pushes towards the tonic. m7♭5 and dim7 are rarer, tension colours: they appear just before a resolution. Listening to music in these styles with this list in mind is a great ear exercise.
Just as you harmonised the scale in triads, you can stack four scale notes on every degree. Using only notes of C major, the result is always the same pattern of qualities:
| Degree | I | ii | iii | IV | V | vi | vii |
|---|---|---|---|---|---|---|---|
| In C | Cmaj7 | Dm7 | Em7 | Fmaj7 | G7 | Am7 | Bm7♭5 |
| Type | maj7 | m7 | m7 | maj7 | 7 | m7 | m7♭5 |
Listen to the whole harmonised scale, one chord per bar:
And play it with shapes that fit between frets 1 and 9:
Goal: Play the seven C major seventh chords, one per bar, at 70 BPM without the sound breaking.
Ask someone to play (or play yourself with your eyes closed, picking at random) Cmaj7, C7 or Cm7 using the root-on-5th shapes. Clues: maj7 sounds bright and still; 7 sounds tense, eager to move; m7 sounds dark but relaxed.
Goal: Get 8 out of 10 identifications right in a row by ear.
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