Why the chord's job matters
Every chord in a key has a job. Home chords (I, vi) rest. Away chords (ii, IV) leave home. The tension chord (V) pulls back. A colour note works best when it suits the job: a soft major 7th on a home chord, a pulling dominant 7th on the tension chord, a mellow minor 7th on an away chord.
Four quick rules of thumb
- Major chords (I, IV): add a major 7th, a 9th or a 6th.
- Minor chords (ii, vi, i): add a minor 7th, then a 9th or 11th.
- The V chord: use a dominant 7th for pull, a sus4 to delay it, and altered notes for drama.
- The iii chord: stick with the minor 7th. The 9th clashes.
To try these on your own song, use the Reharmonise tool. To learn them step by step, follow the Colour Your Chords program. For the theory behind the chords themselves, see seventh chords, suspended chords and 6th and 9th chords.
Frequently asked questions
When can I use a 7th chord?
Almost anywhere, with one caution: the kind of 7th matters. On the V chord use the dominant 7th (G7 in C), which pulls home. On I and IV use the major 7th (Cmaj7, Fmaj7), which sounds soft. On ii, iii and vi use the minor 7th (Dm7, Em7, Am7). A dominant 7th on I or IV sounds bluesy, which is great in blues and restless in a ballad.
When can I use a sus chord?
A sus chord replaces the 3rd with the 2nd or 4th, so it feels unresolved and wants to move. Use it before the plain chord (Csus4 to C, or Gsus4 to G7) or as a floating colour on its own. It works on I, IV and V; the V7sus4 to V7 move is especially common.
When can I use a 9th, 11th or 13th?
Add the 9th to nearly any major or minor chord except iii (its 9th is only a half step above the root). 11ths suit minor chords such as ii, vi and i. 13ths suit dominant chords (V7 and VII7) and major chords in jazz. Always check the melody: the extra note should not fight the note the singer holds.
Which chord can I not use a 7th on?
You can use a 7th on any chord. The point is to pick the right one. The "wrong" choices are the ones that change the chord's job: a major 7th on V stops it pulling home, and a dominant 7th on I turns home into a blues chord.
Is there a rule for this?
No rule, only tendencies. If you like how a chord sounds, it is right. This guide shows what usually works so you know what you are choosing.