Extensions of three note chords…
For the most part four note chords are extensions of triads or suspensions. They are built directly from Mixolydian numbering, which is used for the numbering. Major, minor, diminished and augmented are all considered triads because they all CAN be written in this manner – although diminished and augmented often are not.
Always use Mixolydian for the numbers.
These are the basic four seven chords that come directly from modes:
- Major 7
- Dominant 7
- Minor 7
- Fully diminished.
There are also suspended seven chords and six chords…
- Major 6
- Minor 6
- Major 7 with suspended 4
- Major 7 with suspended 2
- Doubly suspended major 7, which technically has 5 notes but belongs in this group.
- Dominant 7 with suspended 4
- Dominant 7 with suspended 2
- Doubly suspended dominant 7, which technically has 5 notes but belongs in this group.
Finally, there are altered chords…
- Augmented dominant 7 chord
- Dominant seven with flat 5
- Major with b5
- Minor with b6