Confessions on the Fretboard: Confession #42

At some point in the future, I'll do a lesson on harmonizing the major scale in 7ths (see Confession #14 - Know What Chords to Play! for a lesson on harmonizing the major scale), but for now I'll provide a cheat sheet that will get you started quickly on 7th chords.

There are three 7th chords that you will commonly encounter. The three chords are:

the major 7th chord,
the dominant 7th chord, and
the minor 7th chord

Let's jump right in and demonstrate the first two chords as G chords and the last chord as an Am chord. Then we'll see how 7th chords fit into a harmonized major scale.

G MAJOR to G MAJOR 7

I have shown the fifth string muted for the G chord to keep things simple. Just let your 2nd finger gently touch the fifth string to mute it.

Notice how when switching from the G major chord to the G major 7th chord, we lower the G on the first string 1 fret. So the cheat sheet lesson here is take an octave of the root note of the chord and lower it a half step to make a major 7th chord.

G MAJOR to G DOMINANT 7

TIP - A dominant 7th chord is usually written like this: G7. No need to put the word dominant in there.

Notice how when switching from the G major chord to the G dominant 7th chord, we lower the G on the first string 2 frets. So the cheat sheet lesson here is take an octave of the root note of the chord and lower it a whole step to make a dominant 7th chord.

A MINOR to A MINOR 7

Notice how when switching from the A minor chord to the A minor 7th chord, we lower the A on the third string 2 frets. So the cheat sheet lesson here is take an octave of the root note of the chord and lower it a whole step to make a minor 7th chord.

HARMONIZING IN 7ths

Back in Confession #14 - Know What Chords to Play! we learned how to harmonize the major scale and how the formula:

I - ii - iii - IV - V - vi - viio

tells us which chords work in a particular key.

I'm going to ignore the viio chord in the 7th chord cheat sheet because, it would hurt my brain to figure out, its got a really weird name, and its used very infrequently.

So summarizing the formula above:

the I, IV and V chords are major chords, and
the ii, iii and vi chords are minor chords

When you harmonize in 7ths, the summary changes only slightly:

the I and IV chords are major 7th chords,
the V chord is a dominant 7th chord, and
the ii, iii and vi chords are minor 7th chords

So the way I remember this is:

the I and IV chords are still major, but they are major 7th. (just add the note that is one fret below the octave)
the ii, iii and vi chords are still minor, but they are minor 7th. (just add the note that is two frets below the octave)

So all you need to remember is that the V is chord is a dominant 7th chord. And really, this is just the V chord with one added note (the note that is two frets below the octave).