Seventh Chords
12 chords in this group
A seventh chord is a triad with a fourth note stacked on top — the seventh degree above the root. That one note is what separates the plain harmony of folk and rock from the harmony of jazz, soul and film scoring: it adds colour, and in one case it adds a pull that the music has to resolve.
Twelve of them, but four do the work
The catalogue lists twelve seventh chords, and the reason there are so many is arithmetic: four triads times three sizes of seventh gives a lot of combinations. In practice four carry almost everything — major seventh (Cmaj7), minor seventh (Cm7), dominant seventh (C7) and half-diminished (Cm7♭5).
The remaining eight are real chords with real uses, but they are specialist tools. A minor-major seventh belongs to melodic minor; a diminished major seventh is a harmonic-major creature you may meet twice a year.
The one that moves and the ones that stay
Only the dominant seventh contains a tritone — between its third and its seventh — and only it demands to go somewhere. C7 wants F. Everything else in this group is a resting chord that happens to be richer than a triad.
That distinction matters more than any label. If you know whether a chord contains a tritone, you know whether it is a destination or a step on the way, and that is most of what harmony asks you to decide.
Seventh chords on the guitar
The open shapes are one finger from chords you already know. Cmaj7 is x32000 — the open C with a finger lifted. Am7 is x02010, Em7 is 020000, C7 is x32310. In each case the change is smaller than the change in sound.
Higher up, learn them without the fifth. Root, third and seventh is a complete seventh chord; the fifth adds weight and no information, and dropping it frees the hand for extensions later.
Where they come from in a key
Stack a seventh on each degree of the major scale and the sequence is fixed: maj7 on I and IV, m7 on ii, iii and vi, dominant 7 on V, and half-diminished on vii. Every seventh chord you meet in tonal music is one of these until someone alters it deliberately.
The pair that runs jazz is ii–V–I: Dm7, G7, Cmaj7 in the key of C. It is the same cadence that classical harmony calls subdominant–dominant–tonic, written with four notes instead of three.
How to name them without confusion
Written symbols disagree. Cmaj7, CM7 and C△7 mean the same chord; C7 means something else entirely. Older sheets write C7+ for an augmented fifth, which looks alarmingly like a seventh marking and is not one.
The safe reading is: a bare 7 means a minor seventh over a major triad — the dominant. Anything else has to say so explicitly, with maj, a triangle, or a lowered third in the symbol.
Frequently asked questions
What is a seventh chord?
A triad plus a note a seventh above the root, giving four notes in total.
Which seventh chords should I learn first?
Major seventh, minor seventh, dominant seventh and half-diminished. Those four cover most of the repertoire.
Why does C7 sound unfinished but Cmaj7 does not?
C7 contains a tritone between its third and seventh; Cmaj7 does not, so nothing in it needs to resolve.