The Incomplete Dominant Minor Ninth Chord in Diatonic Common Practice Music

The Incomplete Dominant Minor Ninth Chord in Diatonic Common Practice Music

Take for an example the key of G Major and compare the V & the VII chords.

V (D, F#, A)                                                                        VII (F#, A, C)

Notice the common tones.

Now make the V chord a V7 by adding a C note (D, F#,A, C) – we’ve added another common tone.

Now make the VII chord a diminished 7^th chord (a diminished chord with a diminished 7^th added). A diminished 7^th is a half-step smaller than a minor 7^th – so the diminished 7^th here would be Eb and the chord would be (F#, A, C, Eb).

Now with regard to the V chord there is a chord called the Dominant Minor Ninth Chord. It adds a minor 9^th into the dominant 7^th chord. In this case the notes would be D, F#, A, C, Eb.

Notice how similar this V9 chord is to the VIIdim7.

Now the Dominant Minor Ninth Chord is frequently voiced in an incomplete form—the root note is omitted. Compare now:

V9 (F#, A, C, Eb)                                                                                      VII (F#, A, C, Eb)

They are the same!

Now what to call them?

In Diatonic Common Practice Music, if the Incomplete Dominant Minor Ninth is the V chord and it precedes the I chord, it is analyzed as the V9. This is also true of Secondary Dominant Harmony, when any chord of the original seven harmonized chords of the key are preceded by its Dominant Chord, for example, the V chord in the key of G Major is D and can be preceded in the music by an A Chord.

Analysis would show this A chord as a Secondary Dominant V/V (V of V). If however, the chord we are calling an Incomplete Dominant Minor Ninth Chord is not functioning in the role of Dominant or Secondary Dominant, it would be analyzed as a Diminished Seventh Chord (a Diminished Chord with a Diminished 7^th).

A Diminished 7^th is one-half step smaller than a Minor 7^th. It will be the same sound as a Major 6^th but will be called a Diminished 7^th. For example, in the Key of G Major the VII chord is F# Diminished (F#, A, C) and the diminished 7^th would be called Eb.