Extension of the Triad
We know that chords are made up of three distinct pitches (triads). In this chapter, we will learn about chords made up of four distinct pitches. Chords with four or more distinct pitches are called extended chords.
There are a few different kinds of extended chords. The extended chord we will looking at in this chapter is the dominant seventh chord. Dominant seventh chords are formed by adding a minor 3rd to the top of a major chord in root position.
(Chapter 24 – Audio Sample 1)
In the preceding diagram, a minor 3rd (‘D’ to ‘F’) was added to the top of a ‘G major’ chord in root position. The name “dominant seventh”, comes from the fact that the chord is built on the fifth pitch of the scale (the dominant pitch), and from the fact that the interval between the top and bottom pitches is a 7th.
Note: the 7th in a dominant seventh chord is always a minor 7th (10 half steps).
The dominant seventh chord is abbreviated with a superscript 7. We pronounce the chord as ‘G seven’ (G7), not ‘G seventh’.
The following diagram illustrates how the dominant seventh chord is built on the fifth pitch of the scale (the dominant pitch). When we name this chord by its scale degree, we call it ‘V7’ rather than ‘G7’.
As you can see, the Roman numeral ‘V’ signifies the chord’s place in the scale. The superscript 7 signifies the interval between the top and bottom pitches. We know that the ‘V’ chord has a strong tendency to return to the ‘I’ chord. The same holds true for the ‘V7’ chord, since it is an extended version of the ‘V’ chord. (Extending the chord does not change the underlying major chord; it only adds flavor to the existing sound.)
Dominant Seventh Inversions
We know that for chord inversions, we found that a chord with three pitches could have three different arrangements of its pitches: root position, 1st inversion and 2nd inversion. Since dominant seventh chords have added pitch, a ‘3rd inversion’ is now possible.
Remember: inversions are formed by moving the lowest pitch of the chord an octave higher so that it becomes the highest pitch.
(Chapter 24 – Audio Sample 2)
The root of the dominant seventh chord is the lowest pitch when it is in root position. To determine the location of the root in the inversions, identify the interval of a 2nd.
The root will always be the upper pitch in the 2nd. Here is a helpful way to remember which inversion is which. If the root is the ‘1st’ pitch from the top, the chord is in ‘1st’ inversion. If the root is the ‘2nd’ pitch from the top, the chord is in the ‘2nd’ inversion. If the root is the ‘3rd’ pitch from the top, the chord is in ‘3rd’ inversion.