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Lesson 2 - Diatonic seventh (major key)

In jazz, the triad is rarely used except as an effect. The basic unit of jazz harmony is a four-note chord, the diatonic seventh.

Because there are seven individual tones in a major scale, there are seven chords which are diatonic to any key. For example, in the key of C the following chords are diatonic:

Diatonic seventh chords in key of C
major
mode I II III IV V VI VII
basic chord Dm7 Em7 G7 Am7
tones c-e-g-b d-f-a-c e-g-b-d f-a-c-e g-b-d-f a-c-e-g b-d-f-a
intervals 1-3-5-7 1-b3-5-b7 1-b3-5-b7 1-3-5-7 1-3-5-b7 1-b3-5-b7 1-b3-b5-b7

Notice that these chords are built by stacking thirds above each tone in the major scale. Four types of chords have been formed in the above example. The I and IV chords are major sevenths (1-3-5-7), the II, III and VI chords are minor sevenths (1-b3-5-b7), the V chord is a dominant seventh (1-3-5-b7), and the VII chord is a minor seventh with a flatted fifth (1-b3-b5-b7).

In these lessons we will use the following abbreviations:

Abbreviations of the different chord types
abbreviation description mode
maj7 or Δ major seventh chord I, IV
min7 or m7 minor seventh chord II, III, VI
7 dominant seventh chord V
m7(b5) or Ø minor seventh flat five VII

The minor seventh (b5) chord is called a half-diminished chord by some authors. I will not use this terminology because it has not yet gained full acceptance.

In every key the I and IV chord: are major sevenths, the II, III, and VI are minor sevenths, the V is a dominant seventh, and the VII chord is a minor seventh flat five. The following chart shows the chords in every key as played in jazz.

Jazzchords in every key
key \ mode I II III IV V VI VII
C Dm7 Em7 G7 Am7
Db DbΔ Ebm7 Fm7 GbΔ Ab7 Bbm7
D Em7 F#m7 A7 Bm7 C#Ø
Eb EbΔ Fm7 Gm7 AbΔ Bb7 Cm7
E F#m7 G#m7 B7 C#m7 D#Ø
F Gm7 Am7 BbΔ C7 Dm7
Gb GbΔ Abm7 Bbm7 CbΔ Db7 Ebm7
G Am7 Bm7 D7 Em7 F#Ø
Ab AbΔ Bbm7 Cm7 DbΔ Eb7 Fm7
A Bm7 C#m7 E7 F#m7 G#Ø
Bb BbΔ Cm7 Dm7 EbΔ F7 Gm7
B C#m7 D#m7 F#7 G#m7 A#Ø

If you want to take a standard progression such as Dm-G-C, you can transform it to a jazz sound by adding the diatonic seventh to each chord, and it becomes Dm7-G7-CΔ. Play both progressions and notice the difference in sound and style. The progression is II-V-I (in C major) which is a very commonly used progression. The progression Bb-A°-Dm-Gm-Cm-F-Bb in standard harmony becomes BbΔ-AØ-Dm7-Gm7-Cm7-F7-BbΔ in jazz harmony. Any progression can be treated in this manner, however, beware that you do not destroy the basic character of the tune through jazz-ization. Some tunes (often in folk and rock music) rely solely on their triadic character for their strength and the use of diatonic sevenths can destroy a fine tune. On the other hand, tunes which lend themselves to a jazz rendition should be voiced with diatonic sevenths rather than basic triads.

Finally, the knowledge of diatonic sevenths is essential in improvisation. For example: if you realize that the progression cited above (BΔ-AØ etc.) is formed by stacking the notes of a Bb major scale, then it becomes self-evident that a Bb major scale should be used in improvising over that progression. The process of determining what scale a certain progression is based upon is called finding the key center. Most jazz tunes have numerous key centers. For example:

|Dm7	G7	|CΔ	Cm7	|F7	BbΔ	|

The first three chords are diatonic sevenths in the key of C, the last three are diatonic to the key of Bb. Consequently, you would use a C major scale over the first three chords and a Bb major scale over the last three chords.

Try to zero in on V and VII chords because they immediately determine the key center. A G7 occurs only in C major. A BØ occurs only in C major. However, a CΔ is diatonic to C major and G major. A Dm7 is diatonic to C major, Bb major, and F major. Try to determine key centers whenever you play in whatever type of music you play.

Diatonic sevenths

Chord types generated by major scale

Major seventh, seventh, minor seventh, minor seventh flat-five

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