Dominant 7ths

Seventh Chords

After looking at major seventh chords, it’s time to get hip to dominant seventh chords, also called just plain old “seventh” chords. While these still have a major tonality, the seventh degree is a half-step lower than the major seventh which gives it a much different character.

The Sound

Cmaj7 and C7, side-by-side

Let’s do a little side-by-side comparison to get the tonal differences in our ears. Here are two chord shapes: on the left is the major seventh, and on the right is just a plain old dominant seventh chord. Play one and then the other and pay attention to the difference in their character.

You should only need to lift your middle finger up to move from the major 7th to the dominant 7th. That’s it. That’s the only difference between the two. The major seventh is made up of the 1st, major 3rd, perfect 5th and major 7th. The dominant 7th is made up of the 1st, major 3rd, perfect 5th and minor 7th.

The Theory

While the major seventh has a sweet and sunny sound to it, the dominant seventh sounds a little more “angular”. There’s a really good reason for that. The interval between the major 3rd and minor 7th degrees is a tri-tone. You may recall that the tri-tone (or diminished 5th or ♭5) is one of the most dissonant intervals in western music.

Vocal groups often talk about the “rub” of different notes when sung together. Different intervals produce different kinds of textures when played (or sung) together. The “rub” of the dominant 7th chord comes from the presence of the tri-tone and is what gives 7th chords their sound.

The Shapes

Okay, enough theory for now. Let’s look at how the scales, arpeggios and chord shapes layout on the fretboard. We’ll stick with the key A and work our way up the neck. Let’s start with the A root note at the 5th fret of the 6th string. The scale, arpeggio and chord at that position looks like this:

This is the first time we’ve looked at a scale that wasn’t the major scale. Instead of 1-2-3-4-5-6-7, we have 1-2-3-4-5-6-♭7. This is a mode of the major scale (called the “Mixolydian” mode) and we’ll get into these in later lessons.

These shapes are based off of the “G” shape from the CAGED system.

Moving up the neck, we get these shapes rooted around the 4th and 5th positions:

These are the “E” shapes in the CAGED system.

The next shapes are at the 6th and 7th positions. These are the “D” shapes:

Moving further up, we get to the 9th position and our “C” shapes:

The last set of shapes are rooted at the 11th and 12th positions and are the “A” shapes:

In the Wild

Dominant 7 chords are everywhere in western popular music, particularly jazz. You may have noticed that there’s only one dominant seventh in the harmonized major scale, but that doesn’t keep songwriters from using dominant 7 chords everywhere.

Heck, even a plain old 12-bar blues can be played entirely with seventh chords:

12-bar blues in A playing entirely with 7th chords

A lot of early rock-and-roll from the 50’s and 60’s relies heavily on dominant 7th chords. Just listen to any Beatles tune before Sgt. Pepper—they’re loaded with them!

Terminology

You might be wondering where the term “dominant” comes from. Does this chord boss the other chords around on the musical playground? What’s with that name?

When we first looked at seventh chords we harmonized the major scale. Music theory people give each of those chords a unique name based on their traditional role in western music.

Root Note Chord Type Name
1 major 7 Tonic
2 minor 7 Super-tonic
3 minor 7 Mediant
4 major 7 Sub-dominant
5 7 Dominant
6 minor 7 Sub-mediant
7 dim 7 Leading

Don’t get too hung up on all of those names since they’re usually only used when talking about composition and music theory. The term “dominant” is often attached to 7th chords just to make it clear what kind of 7th chord we’re talking about. If somebody says “7th chord” what they usually mean is a dominant seven chord, not a major 7, not a minor 7 and certainly not a diminished or augmented 7th chord.

In the next lesson, we’ll look at the most common type of 7 chord, the minor 7.

Rock on!