When To Play A Seventh Chord

Marcel Ardans

Have you ever heard someone drop a seventh chord into a chord change and it just didn’t work?
Why do some chord changes have seventh chords and others don’t?
Am I missing something here?

Bluegrass chord changes can be a source of confusion, but let me drop this bomb on you: the changes are simple, you can make them infinitely more complicated or less complicated. It’s all up to you, all you need to know are some simple rules to get started. In this article we’ll be focusing on dominant seventh chords and when they make sense in a chord change and the consequences and benefits of including them or leaving them out.

MAJOR SEVENTH VS. DOMINANT SEVENTH

One important thing to define before we get going is the difference between a major seventh chord (e.g. Gmaj7) and a dominant seventh chord (e.g. G7). This article concerns the latter but for the sake of a complete understanding let’s define both.

A major seventh chord (e.g. Gmaj7) is a chord comprised of the root, major third, perfect fifth, and the major seventh. The root, third and fifth build a major triad or simple major chord; but the inclusion of the major seventh (i.e. the seventh note of the major scale) makes this a major seventh chord. Major seventh chords feel slightly whimsical and may be familiar to you as the I chord in a major jazz context.

Our focus today is the dominant seventh chord (e.g. G7), a chord comprised of the root, major third, perfect fifth, and minor seventh (the minor seventh interval is colloquially referenced by many names, such as dominant seventh or flat seventh). Once again, the root, third and fifth build a major triad; but the minor seventh (i.e. the seventh note of the major scale flattened by one half-step) makes this a dominant seventh chord. The dominant seventh chord carries tension and implies motion. A traditional dominant chord function would be to resolve to the tonic or I chord. In the case of G7, this dominant seventh chord would likely resolve to the tonic C major and we would classify that chord change as an authentic cadence.

So in summary of their differences, a major seventh chord is traditionally used as a slightly more harmonically interesting I chord. Where as a dominant seventh chord is traditional used as a V (five) chord leading to the I (one) chord, completing a dominant to tonic motion or authentic cadence.

V - I

Here’s the neat thing, whenever your current chord has a relationship of V to the forthcoming chord you can sub in a dominant seventh chord. In the key of G, an obvious example would be D moving to G. If G is ‘one’, then D will be ‘five’ (i.e. 1, 2, 3, 4, 5 = G, A, B, C, D). So moving from D to G would be V to I. That means the chord change could be amended to D7-G, or D-D7-G.

Here’s another example in the key of G, if I have a G chord moving to a C chord we would traditionally analyze that as I to IV. Which is true, that’s not incorrect. However, if we analyze the distance from G to C we can see that they also share a V-I relationship (i.e. 1,2,3,4,5 = C, D, E, F, G). So this chord change from G to C could possibly be dressed up as G-G7-C.

As long as we have that relationship between starting point and destination it will work. For instance, when going from C to G a dominant seventh chord won’t do us any good because they don’t have the fifth relationship. If G was I, then C would be IV. Unfortunately the dominant seventh chord doesn’t help a IV to I movement, however…

BLUES

When playing a basic 12 bar blues every chord is a dominant seventh chord. In the key of G, the progression would be made up of G7, C7, and D7. So sometimes the cards are aligning and we’re getting a V to I feeling with those dominant seventh chords but a lot of the times we’re not. So how’s that work? Well assuming the melody or break being played is largely minor pentatonic, all the chords can be dominant and it actually helps the soloist. Because the notes that are added to these chords to make them dominant seventh chords (F, Bb, and C) all come from the minor pentatonic scale. This has less to do with traditional harmonic structure and music theory and more to do with everyone using the same pallette.

Now these two sounds can be your archetypes. Ask yourself, does this song sound more bluesy or more major? If it’s more bluesy, put in your dominant seventh chords wherever and see what happens. If this hypothetical song sounds more major, look for those V to I relationships to sneak in your dominant seventh chords and listen to the results carefully.

No matter what it’s important to listen to your results carefully. A melody, the vocal harmonies around a melody, or a soloists note choice can all influence the viability of a dominant seventh chord. More than anything it has to do with the type of sound you want to create. In the words of my friend Brad, “Play what you feel, unless what you feel sucks.”