Blues harmony primer

For a more detailed and scholarly version of this guide with a bibliography, see my Blues Tonality treatise. See also this post on blues melodies.

I enjoy reading r/musictheory, partially because it’s a good way to hone my theory pedagogy chops, and partially because I am a big nerd. There’s a recurring question on the sub about how chords relate to the blues scale, or how you generate chords from the blues scale. This is a typical example:

Wanted to get into some rock music and a lot of those songs use major or minor blues scales. My question is what are the chords within those scales?

This one too:

Previously, I learned that the melody generally uses notes from the scale corresponding to the underlying chord. Recently, I started watching some videos about the blues scale and I notices people were playing major or minor blues scales over various dominant 7th chords(mostly I7 or IV7).

This confusion is understandable. Music theory books and classes rarely mention the blues at all, and when they do, they often misrepresent or oversimplify it, so amateurs are left repeating mythology to each other. Blues is a difficult subject to teach! It has never been systematized, and probably never will be. The best we can hope for is to look at common practices in the music, and see what tropes and patterns we can identify. In the rest of this post, I talk through my best understanding of what the “blues scale” is, the most commonly used blues chords, and a possible explanation for them both.

If you take away nothing else from this post, take away this:

There is no such thing as “the blues scale”

Blues has characteristic pitch collections and melodic patterns, but they can not be meaningfully abstracted down to a scale. There have been a variety of pitch collections that people have named “blues scales”, but all of them are oversimplifications at best.

The most commonly referenced “blues scale” is the minor pentatonic scale with an added sharp fourth/flat fifth. Here it is in E:

This is sometimes called the “Aebersold blues scale” because it was first described in print by Jamey Aebersold in his 1967 book How to Play Jazz and Improvise. This is the first scale that many guitarists learn, because it falls naturally on the fretboard and is easy to play.

If you rotate the Aebersold scale to start on its sixth degree, you get the “major blues scale”, the major pentatonic scale with an added sharp second/flat third. Here is the E “major” blues scale, which uses the same notes as the C-sharp Aebersold scale:

Other scales that have been named “blues scales” include Dorian mode played over a dominant chord backing (so, E Dorian over an E7 chord); the union of Dorian and Mixolydian; Mixolydian mode itself; and the union of minor and major pentatonic.

The problem with all of the aforementioned scales is that they do not account for the blue notes, pitches that fall in between the piano keys. You can reach these notes by bending strings on the guitar, or by using a slide. Singers find them intuitively. You can not play blue notes on the piano, but you can imply them by playing the keys on either side of them and releasing one of them quickly. You can hear this idea in the melody of “Blues Five Spot” by Thelonious Monk.

The blue notes are not discrete pitches. Instead, the blues uses pitch zones that span multiple piano-key notes. The three most commonly used pitch zones in the blues are:

• between 2^ and 3^ (between F-sharp and G-sharp in the key of E)
• between 4^ and 5^ (between A and B in the key of E)
• between 6^ and b7^ or a little past it (between C-sharp and D in the key of E)

The various “blues scales” are really simplified versions of the pitch zones.

This raises a question: why do blues musicians use those pitch zones and not others? For example, you hardly ever hear blues musicians bend in between the major third and the fourth, even though they routinely explore the regions below the major third and above the fourth. I give a possible explanation at the end of the post.

Chords in the blues

Blues was probably originally a vocal music only, and harmonic accompaniment was added later. The simplest chord progression found in the blues is no chord progression at all. There are plenty of classic blues tunes that are based on drones, pedals, or repeated riffs on single chords. Examples of one-chord blues include:

• “Still a Fool” by Muddy Waters
• “Spoonful” by Howlin’ Wolf
• “I’m Bad Like Jesse James” by John Lee Hooker
• “Chain of Fools” by Aretha Franklin

But what is this one chord? If the song is in E, you might think of the chord as E7 or Em, or as a combination of both: an E7 chord with an added G-natural. This chord is sometimes written as E7#9, otherwise known as the Hendrix chord.

If a blues tune has two chords, they will usually be I7 and IV7 (E7 and A7 in the key of E.) Examples include “Boogie Chillen” by John Lee Hooker and “My California” by Lightnin’ Hopkins, along with uncountably many funk and R&B songs.

When people talk about “blues chords”, they usually mean the combination of I7, IV7 and V7 (E7, A7 and B7 in the key of E), typically organized into the famous twelve-bar blues form. However, it is important to recognize that many blues songs don’t use the twelve-bar form, and that there are many non-blues songs that do use the twelve-bar form. So “twelve bar blues” is not the same thing as blues generally.

To find more chords that sound good in the blues, you can use the minor pentatonic scale as a set of roots, and add major triads on top. In E, that gives you the chords E, G, A, B, and D. You can also build your chords on the Aebersold scale, which includes the sharp fourth/flat fifth (A-sharp/B-flat). It sounds better to use a diminished chord on the sharp fourth/flat fifth rather than a major chord. In E, that gives you the chords E, G, A, A♯°, B, and D. You can also add sevenths and higher extensions to these chords:

• E7, E9, E13, E7#9
• G6, Gmaj7
• A7, A9, A13
• A♯°7
• B7, B9, B13, B7#9
• D7, Dmaj7

Hear these chords in action:

For a jazzier sound, you can combine the chords listed above with any chords from parallel major or minor keys. For example, in E blues, you might also use these chords from E major:

• Emaj7
• F#m7
• G#m7
• Amaj7
• C#m7

as well as these chords from E minor:

• Em7
• F#ø7
• Gmaj7
• Am7
• Bm7
• Cmaj7
• D7

There is a common turnaround figure that combines iim7 with the blues diminished chord.

There is one other characteristic blues chord, the bVI7 chord, sometimes called the minor blues subdominant. I call it the Pink Panther chord. In E blues, it’s C7. Sometimes it functions as a substitute dominant for the V7 chord, but it can also lead to I7 or IV7.

Melody and harmony are more independent in the blues than they are in Western European music. Blues melody follows its own rules of tension and resolution that do not need to respect the voice leading or function of the underlying chords. Any melody can be embellished or replaced by blues scales and blue notes and it will still fit with any underlying chord progression. For example, compare Aretha Franklin’s version of “Bridge Over Troubled Water” with the original by Simon and Garfunkel. While she mostly plays the same chords, Franklin replaces the entire melody with blues ideas of her own.

The blues is a groove-based music, using short, repeating chord progressions. The chords in loop-based grooves create a sense of states, conditions, or “places to be”, rather than acting as components of a large-scale tonal scheme. While the chord progressions in the blues might resemble Western European tonal harmony, they do not follow the same rules. In European harmony, a B7 chord in the key of E conventionally “wants” to resolve to E. In the blues, it does not necessarily, and it will just as often move to A7. According to Western tonal theory, E7 similarly “wants” to resolve to A. In the blues, E7 can be a resolved and settled sound in the key of E.

Does blues harmony come from the overtone series?

The ethnomusicologist Gerhard Kubik argues that blues harmony originates in traditional West African tuning systems based on the first seven natural harmonics of notes a fourth apart (E and A in the key of E.) Many classic blues recordings were made on Hohner harmonicas tuned in such a system. Here is a reference guide to the locations of the harmonics on a guitar relative to the fretboard. In the video below, Miles Okazaki demonstrates the first seven harmonics of the guitar, first on the A string, then on the other strings.

The first seven harmonics of the E string produce the following pitches:

1. E2
2. E3
3. B3
4. E4
5. G#4 (a little flatter than the standard pitch)
6. B4
7. D4 (much flatter than the standard pitch)

The first seven harmonics of the A string produce the following pitches:

1. A2
2. A3
3. E4
4. A4
5. C#5 (a little flatter than the standard pitch)
6. E5
7. G5 (much flatter than the standard pitch)

Harmonics four through seven on the E and A strings produce just intonation E7 and A7 chords. This diagram shows the chords mapped to the closest piano-key pitches.

You can also arrange these notes into a just intonation “blues scale”: E, (very flat) G, (slightly flat) G-sharp, A, B, (slightly flat) C-sharp, (very flat) D. If you map these to the closest piano-key notes, you get the union of the E major pentatonic and E minor pentatonic scales.

If you add the eleventh harmonic of E and some other intervals derived from the ones above, you can see possible origins of the Aebersold blues scale and the blues diminished chord.

Kubik’s argument is a speculative one. Since blues was not recorded until the 20th century and was not transcribed accurately before that time, we will probably never be able to reconstruct its origins. It might simply be a coincidence that Kubik’s just intonation intervals happen to lie within the blues pitch zones. There may be a completely different explanation, and there may not be any explanation at all.

Blues and the harmonica

If you want to play blues harmonica, you have to confront the very confusing fact that you are supposed to use an instrument tuned to a different key than the key you want to play in. If you want to play blues in E, you will need a harmonica in the key of A. This is because blues musicians play the instrument differently from the way its inventors intended.

Blowing into a harmonica produces a major triad repeated in octaves. Drawing through the harmonica produces a dominant ninth chord, the V7 in the key of the blown triad. Blowing into an A harmonica produces an A chord, and drawing through it produces an E9 chord (E7 with an added F-sharp).

At some point, Black American musicians realized that if they mentally reversed the roles of the blown and drawn notes, they could get a very different sound out of the harmonica. If you take an A harmonica and think of the drawn notes as the tonic chord, then you can play it in E blues. Furthermore, you can bend the drawn notes flat to get the pitch zones. In the mid-20th century, Hohner’s popular Marine Band harmonicas were tuned to play just intonation major thirds and harmonic sevenths on the drawn chords, so they produced blue notes out of the box.

Teaching the blues

Well-intentioned music educators often teach the blues by having students improvise using the Aebersold scale over a 12-bar blues backing. I know that the constraints of this approach can be liberating; there are no “wrong” notes and everything sounds reasonably bluesy. I went to a talk with Jon Batiste where he said that he started playing the music that way, and if it’s good enough for him, it should be good enough for anybody. However, Jon Batiste was clear that he almost immediately moved beyond the Aebersold scale and into the music’s full complexity through deep aural immersion. We need to make sure that students understand that the Aebersold scale represents only one aspect of a vast and deep folkloric world, and that they need to learn how the blues works from the music itself.