48: Diatonic 7ths
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Lesson 48: Diatonic 7thsThis lesson teaches the diatonic 7th chords, which are used in the chord progressions in many songs.
Before taking this lesson, you should know:
The diatonic 7th chords are the obvious combination of two ideas: diatonic triads and 7th chords.
As you know, the diatonic triads are 3-note chords built on the scale degrees of the song's key:
The diatonic 7th chords are just 4-note chords built the same way:
If you understand how we figured out the diatonic triads, then you could figure out the diatonic 7th chords yourself, so I won't go through that process here, I'll just show the results:
The Common Major-Key Diatonic 7th Chords are:
Imaj7 IIm7 IIIm7 IVmaj7 V7 VIm7
(That's "one major seven, two minor seven, three minor seven, four major seven, five seven, six minor seven".)
The Common Minor-Key Diatonic 7th Chords are:
Im7 ♭IIImaj7 IVm7 Vm7 ♭VImaj7 ♭VII7
(That's "one minor seven, flat-three major seven, four minor seven, five minor seven, flat-six major seven, flat-seven seven".)
Here are charts of these chords in the common keys:
How These 7th Chords Are Used
Diatonic 7th chords aren't usually just thrown into a song with triads for "no reason". They're usually used one of these ways:
"Jazzy" styles. In jazz, 7th chords (and even more complicated chords) are usually used everywhere instead of triads. 7th chords are also often the usual chords in "jazzy pop" styles like soul and disco. In fact, you can make a simple "jazzy version" of a triad-based song just by changing all the diatonic triads to diatonic 7th chords.
To create a melodic line. In pop styles, an occasional 7th chord might be used because it creates a strong melodic line. This melodic line might be in the actual melody, or in the bass line, or in an inner voice in the chords. A "strong melodic line" usually means a line that either:
To explain the melody. Sometimes, the instruments are just playing a triad, but the melody is singing the 7th of the chord, and the easiest way to explain why the melody note "works with the chord" is to just say that the "analysis chord" is a 7th chord, even though the "instruments chord" is just a triad.
You can add these activities to your writing exercises (from Lesson 2: Practicing Songwriting):