Seventh Chords

A triad with one more third on top: four notes, a root, a third, a fifth and a seventh. That one note is where most of harmony's color lives — a major seventh sounds like a held breath, a dominant seventh like a question, a minor seventh like a room with the lights down — and there are three seventh chords that matter before any other. Above is C7 on the guitar, one shape at a time; the capsule changes the chord, the root chip the key, the picker the instrument, ‹ › walks the shapes, and the preset beneath opens the same figure on the shells. The figure follows the text from here.

One more third

C major, then the seventh added

Stack thirds on C: C, E, G — a major triad — and one more, B: Cmaj7. The fourth note is a third above the fifth and a seventh above the root, and it is what the chord is named for. A tetrad is any four-note chord built this way, and on the instrument it is the triad's shape with one note added — usually where a doubled root used to be.

Three qualities

maj7, 7, m7: the seventh drops, then the third

Which third you add, and to which triad, decides the chord. A major triad with a major third on top — the seventh a semitone under the octave — is a major seventh, Cmaj7. The same triad with a minor third on top — the seventh a whole step under the octave — is a dominant seventh, C7. A minor triad with a minor third on top is a minor seventh, Cm7. Watch the wheel: from maj7 to 7 the seventh drops a semitone; from 7 to m7 the third does. Two notes, three chords, and the whole vocabulary of a lead sheet.

What each one does

The dominant seventh is the one that wants something: its third and seventh are a tritone apart, and they resolve by a semitone each into the chord a fifth below — G7 into C, the cadence every song ends on. The major seventh is the one that rests, the tonic's own color; the minor seventh is the one that sits between, the ii of a ii–V–I and the chord of every vamp. Hear the three on one root and you have heard the three jobs a chord can do.

Where the seventh sits

On a string instrument the seventh usually takes the place of a doubled root: the E-shape's root on the D string comes down a whole step for a 7, a half step for a maj7. Seventh chords in the CAGED shapes goes through the five guitar forms; on a keyboard the seventh is the note just under the next octave, the little finger's key. Set the shape menu to "Basic shapes" and walk C7 up the neck to see it in each shape.

In a key

The seventh chord on every degree of a major key: Imaj7, ii7, iii7, IVmaj7, V7, vi7 — two major sevenths, three minor sevenths and exactly one dominant seventh, on the V. That one is how the ear finds the key, and the ii–V–I is three chords of the row. Chords in a key on "Tetrads" draws each inside the scale it comes from, with a page for every key.

The shells

Four notes are one more than you need; the shell voicings keep the root, third and seventh and drop the fifth — three notes that carry the chord, and the grips a ii–V–I is actually played with.

On the guitar

C7 on the guitar: the five open seventh chords — C7, A7, G7, E7, D7 — are the CAGED forms with one note changed, and they move up the neck the same way. Two barre shapes, E7 and A7, cover most needs; the shells cover the rest.

On the piano

Cmaj7 on the piano: four keys under one hand, thumb on the root, little finger on the seventh — or the seventh in the left hand and the triad in the right. A seventh chord on the piano is the clearest picture of the stack: skip a key three times.

On the ukulele

C7 on the ukulele: four strings, four notes, so a seventh chord is the one chord a ukulele plays complete without doubling — which is why sevenths sound so at home on it.

On the bass

C7 on the bass: a bassist outlines the chord — root, third, fifth, seventh in a line — and the seventh is the note that tells the band which chord is coming.

On the mandolin

C7 on the mandolin: four courses, four notes, the fifths tuning putting the seventh on the string above the root.

Hearing them

The app's tetrad games deal a seventh chord, show its root and ask for the shape — the quality from the third and seventh, the grip from the root. Build Shapes with seventh chords is that game; on this site the triads' version runs without a mic, and the sevenths join it.