Lesson 49: Diatonic 7ths

This 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 triads (Lesson 29: Minor Key Triads)
7th chords (Lesson 31: 7ths Games)

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:

Degrees 1, 3, 5
Degrees 2, 4, 6
Degrees 3, 5, 7
etc.

The diatonic 7th chords are just 4-note chords built the same way:

Degrees 1, 3, 5, 7
Degrees 2, 4, 6, 8
Degrees 3, 5, 7, 9
etc.

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:

Key	Imaj7	IIm7	IIIm7	IVmaj7	V7	VIm7
A♭ major	A♭maj7	B♭m7	Cm7	D♭maj7	E♭7	Fm7
A major	Amaj7	Bm7	C♯m7	Dmaj7	E7	F♯m7
B♭ major	B♭maj7	Cm7	Dm7	E♭maj7	F7	Gm7
B major	Bmaj7	C♯m7	D♯m7	Emaj7	F♯7	G♯m7
C major	Cmaj7	Dm7	Em7	Fmaj7	G7	Am7
D♭ major	D♭maj7	E♭m7	Fm7	G♭maj7	A♭7	B♭m7
D major	Dmaj7	Em7	F♯m7	Gmaj7	A7	Bm7
E♭ major	E♭maj7	Fm7	Gm7	A♭maj7	B♭7	Cm7
E major	Emaj7	F♯m7	G♯m7	Amaj7	B7	C♯m7
F major	Fmaj7	Gm7	Am7	B♭maj7	C7	Dm7
F♯ major	F♯maj7	G♯m7	A♯m7	Bmaj7	C♯7	D♯m7
G♭ major	G♭maj7	A♭m7	B♭m7	C♭maj7	D♭7	E♭m7
G major	Gmaj7	Am7	Bm7	Cmaj7	D7	Em7

Key	Im7	♭IIImaj7	IVm7	Vm7	♭VImaj7	♭VII7
A minor	Am7	Cmaj7	Dm7	Em7	Fmaj7	G7
B♭ minor	B♭m7	D♭maj7	E♭m7	Fm7	G♭maj7	A♭7
B minor	Bm7	Dmaj7	Em7	F♯m7	Gmaj7	A7
C minor	Cm7	E♭maj7	Fm7	Gm7	A♭maj7	B♭7
C♯ minor	C♯m7	Emaj7	F♯m7	G♯m7	Amaj7	B7
D minor	Dm7	Fmaj7	Gm7	Am7	B♭maj7	C7
E♭ minor	E♭m7	G♭maj7	A♭m7	B♭m7	C♭maj7	D♭7
E minor	Em7	Gmaj7	Am7	Bm7	Cmaj7	D7
F minor	Fm7	A♭maj7	B♭m7	Cm7	D♭maj7	E♭7
F♯ minor	F♯m7	Amaj7	Bm7	C♯m7	Dmaj7	E7
G minor	Gm7	B♭maj7	Cm7	Dm7	E♭maj7	F7
G♯ minor	G♯m7	Bmaj7	C♯m7	D♯m7	Emaj7	F♯7

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:

Repeats the same note; -or-
Ascends or descends stepwise for 3 or more notes

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.

Exercises

You can add these activities to your writing exercises (from Lesson 2: Practicing Songwriting):

Practice playing them. Make a list/chart, keeping track of how fast you can play these sequences, in both major and minor keys, in every key. When you can play them all at 120 BPM, you'll know them pretty well.
Analyze chord progressions. Analyze the chord progressions in other people's songs, and when you find a 7th chord, see if you can explain it with one of the "reasons" above.
Analyze melodies. When you're analyzing melodies (see Lesson 48: Embellishing Tones), watch for when the best way to analyze a melody note is to just change the song's triad chord to a 7th chord as the "analysis chord".