A seventh chord adds an interval of a seventh to the root note of a triad:

Dominant seventh chord

The dominant seventh chord is the most common type of seventh chord. It is found in the V degree of major scales. It has a major triad and a minor seventh:

Major seventh chord

The major seventh chord (major triad and a major seventh) is found in the I, IV degrees of major scales:

Minor seventh chord

The minor seventh chord (minor triad and a minor seventh) is found in the II, III and VI degrees of major scales:

Half-diminished seventh chord

The half-diminished seventh chord (diminished triad and a minor seventh) is found in the VII degree of major scales:

Diminished seventh chord

The diminished seventh chord (diminished triad and a diminished seventh) is found in the VII degree of harmonic minor scales:

Inversions

Since they have four notes, seventh chords have up to three inversions:

This table summarizes these five types of seventh chords:

Chord	Triad type	Seventh interval	Chord symbol
Dominant seventh	Major	Minor seventh	C7
Major seventh	Major	Major seventh	CMaj7	CMa7	C▵
Minor seventh	Minor	Minor seventh	Cm7	C-7	Cmin7
Half-diminished seventh	Diminished	Minor seventh	Cm7(b5)	Cø
Diminished seventh	Diminished	Diminished seventh	Cdim7	Co7