Diminished seventh chords, and, pardon the expression, half-diminished seventh chords in jazz and popular music
Diminished seventh chords
In jazz and popular music, diminished chords are invariably played as four-note chords, rather than triads, whether the chord symbol says Cdim (C °) or Cdim7 (C ° 7).
A diminished seventh chord consists of a diminished triad plus a diminished seventh above the root of the triad:
However, enharmonic spellings are fre-quently employed by jazz musicians to helpfacilitate reading. This practice producesresults that can be understandably confus-ing to a classically trained musician.Regrettably, breaking the rules of classicaltheory is a common occurrence in jazz.1
With enharmonic spellings, the diminished seventh of a chord may be notated as a major sixth. Similarly, a diminished fifth will sometimes be notated as an augmented fourth.
When analyzing a diminished seventh chord, one can see that it consists of three minor thirds. In the example below, these minor thirds are found from C to Eb, Eb to Gb , and Gb to Bbb. This is an important point, as we'll see later in this article when we talk about the so-called half-diminished seventh chord.
In order to get the sound of diminished seventh chords in your ears, and the spacing of minor thirds in your fingers, play the following lead sheet several times.
Minor seventh chord with a lowered fifth (half-diminished seventh chord)
I eschew the term half-diminished seventh chord. Jazz musicians coined it, and writers of traditional music theory text-books foolishly adopted that designation for what is, in reality, a minor seventh chord with a lowered fifth. Now we are stuck with the term, though I deliberately avoid using the term "half-diminished," except to point out its meaning to students.
This chord consists of a minor triad with a lowered fifth (a diminished triad), plus a minor seventh above the root of triad. It is often indicated with the chord symbol Dø7.
As pointed out earlier, a pure diminished seventh chord consists of three minor thirds. By contrast, the above chord consists of two minor thirds (D to F and F to Ab) plus a major third (Ab to C). What, then, is the logic of calling the chord half-diminished, when by virtue of its two minor thirds it is actually two-thirds diminished?
I feel that the word "diminished" should be used only in the context of a pure diminished seventh chord, not a partially diminished chord, if there's any such thing.
In today's world of music, any chord may progress to any other chord. But in traditional functional harmony, certain chords have tended to resolve to certain other chords. The classic example of this is the resolution of a dominant chord to the tonic.
In functional harmony the resolution possibilities of a diminished seventh chord are manifold, but governed in many cases by a half-step leading tone pull to a tonic, as shown in the following examples (upper right of page).
Note that because of its interval symmetry, each one of the diminished seventh chords above contains the same pitches asthe other three. Also note that any pitch in a diminished seventh chord can resolve up a half step to a "tonic," as shown above, making the chord extremely versatile. In the next several paragraphs we will see that the so-called half-diminished seventh chord does not offer this resolution dynamic.
The resolution tendency of the so-called half diminished seventh chord (really a minor seventh chord with a lowered fifth), on the other hand, is quite specific. It does not function as a diminished seventh chord, but instead functions as a secondary dominant that has been converted into a minor seventh chord with a lowered fifth. This altered secondary dominant proceeds on to the dominant seventh chord and ultimately the tonic. So, instead of a II7-V7-I (or i), the progression becomes ii7(b5)-V7-I (or i).
In the circle of fifths, the progression would look like this (see circle at right):
In my view, the chord symbol Dm7(b5)is a better indication of the chord's resolution tendency than Dø7. This is another reason why I prefer the minor seventh with a lowered fifth label over the half-diminished label. You'll see this resolution tendency realized several times in the composition "Song," seen below. Note the ii7(b5)-V7-I progression in measures 1-2, 3-4, and 5-6.
Practice this piece repeatedly in order to acquire the sound of this chord in your ears, feel the spacing of the notes under your fingers, and experience playing the ii7(b5)-V7-I progression.
1See my article "Common Errors in Jazz Music Notation" in the September 2009 issue of JAZZed magazine, the official journal of the Jazz Education Network. www.jazzed.com