Each
chord quality has a distinct function (usually expressed as a
Roman numeral) within a chord progression. Most qualities can
have a variety of functions, but the dominant 7th chord has only
one.
The dominant 7th chord always functions as a V7 chord, pointing the progression
to a I chord a perfect 5th down the Circle of Fifths. The
chord quality will not change by extending or altering the basic
chord.
- For example :
- C9 (C E G Bb D)
- C7aug (C E G# Bb)
- C13#11 (C E G Bb D F# A)
- C7sus4 (C F G Bb), or a
- C7b5 (C E Gb Bb)
All above altered dominant chords function as normal C7
chords. They do not change quality but only add colour to
the chord. The same applies for the other chord qualities.
Together the five chord qualities cover almost all chord
functions used in Western harmonies. (A rare exception is the
minorMajor 7th chord, which will be discussed in Session 20.)