While conventional harmony is based on the triad, the basic building block in jazz is the four note chord or tetrad, a basic triad with a 6th or 7th scale degree added. There are 6 basic tetrads that serve as these fundamental building blocks:
- three major
- six chords
- seventh chords (aka: dominant seventh or major-minor seventh)
- major seventh chords (aka: major seventh or major-major seventh)
- three minor
- minor six chords
- minor sevenths (minor-minor sevenths)
- minor-major sevenths
The major six chord uses the exact same notes as the (relative) minor seventh chord. That is to say a C6 (C-E-G-A) uses the very same notes as an Am7 (A-C-E-G). The difference between these two names for the same chord depends on how they are used or how they are voiced. Many arrangers and players use these interchangeably and there are some instances where it is difficult to say which is really the better term.
Dominant 7 Chords
The dominant 7 chord is found more frequently than any other chord in jazz. It is also the basis for a slew of more complex chords, using both natural and altered upper tensions. The dominant seven, often referred to simply as a “seven” chord is used to drive a harmonic progression back to its home key. It is also used in jazz and blues, interchangeably with the tonic chord of the home key. With a very strong and popular sound, this chord has frequent and very flexible application.
The Major Seven (or major-major seven) chord is used often to add color to a chord where a simple triad would be used. It is sometimes interchanged with the 6 chord. It is known for it’s soft, lush sound, not as driving as the dominant 7 but better suited for delicate applications.
Minor Six Chords
The minor six chord is has a slightly esoteric sound and is frequently heard in jazz, particularly in gypsy jazz, a movement spearheaded by guitarist Django Rheinhardt and violinist Stefan Grapelli.
Minor Seven Chord
Of the minor tetrads, the minor seven could be considered the most stable. Rhythm players rely on this chord to play it safe and stay more out of the way of soloists who may veer from the charted path. A pretty sound on its own, this chord is a frequent choice in jazz circles.
Minor Major Seven
This is one of the more colorful of the basic tetrads used in jazz. Cool and exotic, choosing this chord is just on the cusp breaking into the wide world of upper tension chords in jazz, a wonderful, exciting sound.