Shell Voicings

A seventh chord has four notes, and four notes are usually one more than you need. Drop the fifth and what remains — the root, the third and the seventh — is a shell voicing: three notes and everything that makes the chord what it is. The third says major or minor; the seventh says major seventh or dominant. The fifth says nothing that the bass player and your ear don't already know.

Shells are the chords of jazz rhythm playing — the Freddie Green sound on guitar, the left hand's two notes under a pianist's right — and the fastest way through a chart on any instrument. Above is Cmaj7 as a shell on the guitar; the capsule changes the chord, the root chip the key, the picker the instrument, ‹ › walks the shells. The figure follows the text from here.

Three notes that carry the chord

Cmaj7, then its shell: the fifth gone

A major seventh is 1 3 5 7; its shell is 1 3 7. A minor seventh's shell is 1 ♭3 ♭7, a dominant seventh's 1 3 ♭7. Look at what changes between them: only the third and the seventh, one semitone each, and those two notes are the chord's whole identity. The fifth is the same in all three, which is why it can go. On the wheel the shell is the chord with one wedge closed; on the instrument it is the chord with one finger free.

One finger moves

Play Cmaj7, then C7, then Cm7, in one place. The seventh drops a semitone, then the third does. That is a chord changing quality with almost no movement — the whole point of shells, and the reason a ii–V–I can be played with the hand barely leaving the spot: Dm7, G7, Cmaj7. The third of one chord becomes the seventh of the next; the shells are where you see it.

Where the fifth went

Nowhere you'll miss it. The fifth is the note the ear supplies for free — it is the strongest overtone of the root after the octave (the harmonic series shows why) — and it is the note a bass player is most likely to be holding. Leaving it out makes the chord lighter and the change between chords smaller. When you want it back, the full shapes have it; when you want the chord to move, the shell wins.

In a key

The seventh chords of a key are a row of shells a step apart — Imaj7, ii7, iii7, IVmaj7, V7, vi7 — and the ii–V–I is three of them. Chords in a key on "Tetrads" with the useful family on draws each one inside the scale it comes from; the shells make the row playable in one position.

On the guitar

Two grips per quality: Cmaj7 with the root on the A string — root at the third fret, the third on the D string, the seventh on the G — and with the root on the E string. Cm7 and C7 are the same grips with the third and seventh lowered; six shapes cover most standards, and the strings between the root and the third stay muted.

On the piano

Cmaj7 as a shell on the piano: the root in the left hand, the third and seventh together — or the seventh below the third, the two a fourth apart — and the right hand free for the melody. The two-note shell is the first thing a jazz pianist's left hand learns.

On the ukulele

Cmaj7 on the ukulele: four strings and three notes, so the shell is a chord with one string doubled or left out — and with the fifth gone a ukulele seventh chord stops sounding crowded.

On the bass

Cmaj7 on the bass: a bassist arpeggiates the shell rather than sounding it — root, third, seventh in a line is the chord's outline with nothing the band already has.

On the mandolin

Cmaj7 on the mandolin: three courses, the root and the seventh a whole step apart on adjacent strings — the mandolin's version of the guitar's A-string shell.

Beyond the shell

A shell is also the frame you add color to. The note above the seventh is a ninth or a thirteenth waiting to happen; the shape stays and the extension sits on top. That is a page of its own, but the shells are where it starts — and where the chord shape game starts too, once the sevenths join it: hear the chord, know the quality from its third and seventh, find the shell with the root shown.