Seventh Chords

In the previous lessons we saw how a chord is built from three notes, in a stack of thirds. What happens if we don't stop there, but put one more note on top?

01A fourth note, the seventh

Start from a triad, for example C-E-G. If you place one more third on top of it (B), you get the note that sits a seventh above the root. This four-note chord is called a seventh chord.

The extra note, the seventh, gives a sound that "opens up" a little more than the triad. You feel that the sound doesn't close but holds a little tension.

From triad to seventh chord

Triad

C-E-G

With a seventh

C-E-G-B

02The five types

Depending on the type of the triad and the quality of the seventh that is added, different colours emerge. The five basic types are:

The five types

TypeStructureExample

Major seventh (maj7)major triad + major seventhC-E-G-B

Dominant seventh (7)major triad + minor seventhC-E-G-B♭

Minor seventh (m7)minor triad + minor seventhC-E♭-G-B♭

Half-diminished seventhdiminished triad + minor seventhC-E♭-G♭-B♭

Diminished seventhdiminished triad + diminished seventhC-E♭-G♭-B♭♭

The most common confusion is between the major seventh (maj7) and the dominant seventh (7). Their triad is the same, major. They differ only in the note of the seventh, by one semitone.

One note changes the colour

Major seventh

C-E-G-B

Dominant seventh

C-E-G-B♭

03The most important one, the dominant seventh

Of the five types, the dominant seventh is the one you will meet most often in music. It is the chord built on the dominant degree (V) of a scale, with a seventh.

The reason it stands out: its minor seventh creates an internal tension that "asks" to resolve. The interval between its third and its seventh is a tritone, the most "restless" sound in Western harmony. That tension almost always leads toward the tonic chord, which is why the dominant seventh is the driving force behind most cadences in harmony.

In C major the dominant seventh is G-B-D-F (V7), and its resolution goes to the tonic C-E-G (I).