By Desi Serna

The key to playing blues music on the guitar is remembering that all the chords used are some type of dominant 7th chord. In other words, blues chords are any type of chord with a major 3rd and f7th, such as A7, A9, or A13.

Even when the guitar plays chords without f7ths, like plain major chords or 6ths, the tonality of each chord is still treated like that of a dominant 7th, and the melodies, lead guitar solos, and bass lines still feature f7ths.

Dominant 7th chords are drawn from the 5th degree of the major scale. When you build 7th chords (1-3-5-7) for each degree of the major scale, only the 5th degree produces the major triad and f7th necessary for a dominant 7th chord. Blues chords with major 3rds are treated as dominant 7th chords, and all dominant 7th chords are really V7s.

How to play the dominant scale on the blues guitar

According to traditional theory, the appropriate scale to play over a 7th chord is its parent major scale. To determine the parent major scale of a particular chord, you need to first realize that a dominant 7th chord is based on V and then figure out which chord is I from there.

For example, the correct major scale to play over an A7 chord is D because if A7 is V, then D is I. Likewise, you play A major scale over E7 because E is V of A, and you play G major scale over D7 because D is V of G.

When you play a major scale with the 5th degree functioning as the tonic, you’re playing in Mixolydian mode, which is also known as the dominant scale. (In case you’re keeping track, the 5th degree of the major scale is named the dominant, the V chord makes a dominant 7th, and the fifth mode is called the dominant scale. That’s a lot of dominants!).

Here are two types of A dominant 7th chords (A7 and A9) and two A dominant scale patterns in different positions. The parent major scale here is D because A is V of D. So the patterns are simply D major scale, only with the 5th degree, A, numbered as 1 because it’s functioning as the tonic.

[Credit:     Illustration courtesy of Desi Serna]

Credit:     Illustration courtesy of Desi Serna

This includes only a few examples to get you started, but of course you can play A7 chords and A dominant scale patterns (D major scale) all over the neck.

One way you’re likely to hear the dominant scale used in blues-based music is in the bass. Here is an example of how a bass player typically constructs a walking bass line over an A7 chord using notes from the A dominant scale.

[Credit:     Illustration courtesy of Desi Serna]

Credit:     Illustration courtesy of Desi Serna

Blues guitarists also use the dominant scale for melodies, riffs, and solos, though they usually use it in combination with some pentatonic scales. For example, the guitar in “L.A. Woman” by The Doors uses the A dominant scale but also features a few runs in A minor pentatonic.

How to use the major and minor pentatonic on the blues guitar

Blues guitar players love to use pentatonic scale patterns, perhaps because of the easy-to-use box-shaped patterns that the pentatonic scale makes.

Normally, you’d use the major pentatonic to play over a chord with a major 3rd. This remains true for dominant 7th chords and, at times, the blues. This means that you can play A major pentatonic over chords like A, A7, A9 and so on.

Here is a reference A7 chord (based on an E form barre chord) and a few A major pentatonic scale patterns. You can play A major pentatonic anywhere, but these patterns are often favored by guitarists because of their proximity to the common A7 chord shape.

[Credit:     Illustration courtesy of Desi Serna]

Credit:     Illustration courtesy of Desi Serna

While blues players make use of the major pentatonic and the rules of traditional harmony, they usually prefer to break the rules by playing minor over major. This means that the A minor pentatonic gets applied to chords like A, A7, A9 and so on. You see a reference A7 chord and a few A minor pentatonic scale patterns here.

The minor pentatonic scale includes the intervals 1-f3-4-5-f7. Dominant chords are built 1-3-5-f7. The only scale interval here that potentially poses a problem is the f3rd. Because a dominant 7th chord has a major 3rd, the f3rd is going to conflict. But guess what? It works! In fact, the tension between the major and minor 3rd is the most important feature of the blues sound.

[Credit:     Illustration courtesy of Desi Serna]

Credit:     Illustration courtesy of Desi Serna

In blues, a blue note is one sung or played at a slightly lower pitch. Sometimes this alteration is a full semitone, as is the case when going from a minor to major 3rd. Blues players often slide or bend from the minor to major 3rd. Here are a few examples of blues songs that use minor over major:

  • “Give Me One Reason” by Tracy Chapman is based in the key of Fs using chords with major 3rds, but the vocal melody and guitar solos primarily use the Fs minor pentatonic.

  • “Sundown” by Gordon Lightfoot centers on an Fs major chord, but the lead guitar solos play in Fs minor pentatonic.

  • Stevie Ray Vaughan’s “Pride and Joy” is based on an E major chord, but the guitar solos primarily use E minor pentatonic (guitars tuned down one half-step to Ef).