Blues harmony primer

Doing my best to clear up some confusion

For a more detailed and scholarly version of this guide with a bibliography, see my Blues Tonality treatise.

How do chords and scales work in the blues? Is there a "blues scale", and if so, what notes does it include? What are blue notes? Why does it sound good to play minor melody notes over major chords? To answer these questions, I combine my experiences of listening to and playing the music, talking to practitioners, and reading academic sources.

The blues scale(s)

There are several scales that people call "blues scales." The most commonly referenced one 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. The Aebersold scale is not enough for effective blues playing on its own, but it is a reasonably good starting place. 

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:

There is some debate about whether these two blues scales are even "real" scales, or whether they are simply shorthand for more complicated pitch collections. It is more accurate to understand the blues as a set of flexible pitch zones. I explain this idea in the section on blue notes below.

There are many other scales played in the blues. For example, jazz musicians often use Mixolydian and Dorian modes. In E, try playing E Mixolydian and E Dorian.

Blues Chords

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 single chords. Examples of one-chord blues include "Still a Fool" by Muddy Waters, "Spoonful" by Howlin' Wolf, and "I'm Bad Like Jesse James" by John Lee Hooker. But what is this chord? If the song is in E, you might think of the chord as E7 or Em, but it is really 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.

The second simplest blues progression is the two-chord loop. The chords are usually the I7 and IV7 chords (E7 and A7 in the key of E blues.) 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 "the blues chord progression," they usually mean some combination of I7, IV7 and V7 (E7, A7 and B7 in the key of E), often organized into the famous twelve-bar blues form. However, it is important to recognize that many blues songs do not use the twelve-bar form. Also, 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. It will sound 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 Emaj7, F#m7, G#m7, Amaj7 and C#m7 from E major, or Em7, F#ø7, Gmaj7, Am7, Bm7, Cmaj7 and D7 from E natural minor. 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 think of it as the Pink Panther chord. In E blues, it's C7. While its root is from E minor, the chord is otherwise comprised entirely of blues scale notes (E, G and B-flat). Listen to it here.

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.

Chord function in the blues

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 "wants" to resolve to E. In the blues, it does not necessarily, and it will just as often move to A7. According to European tonal theory, E7 "wants" to resolve to A. In the blues, E7 can be a resolved and settled sound. 

Blue notes

To play the blues well, you will need to use pitches that fall in between the piano keys. These are the blue notes. You can reach these notes by bending strings on the guitar, or by using a slide. Singers find them intuitively. You can not play them 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.

Some people argue that the blues is not a system of discrete notes like European keys and modes. Instead, the blues uses pitch zones that span multiple piano-key notes. There are three main pitch zones in the blues:

• Between 2^ and 3^ (F-sharp and G-sharp in the key of E)

• Between 4^ and 5^ (A and B in the key of E)

• Between 6^ and b7^ or a little past it (C-sharp and D in the key of E)

The corollary to this idea is that the various “blues scales” are actually simplified versions of the pitch zones. Panos Charalampidis explains this idea in his YouTube channel.

This raises a question: why do blues musicians use those pitch zones and not others? For example, you hardly ever hear a blues musician bend in between G-sharp and A in the key of E, even though they are constantly exploring the regions below G-sharp and above A. I give a possible explanation in the next section.

Blues and natural harmonics

The ethnomusicologist Gerhard Kubik argues that blues harmony originates in traditional West African tuning systems based on the natural harmonics of 1^ and 4^ (E and A in the key of E.) Here is a a reference guide to the locations of the harmonics relative to the frets. 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 the possible origins of the Aebersold blues scale and the blues diminished chord.

I believe that the blues pitch zones are the result of enslaved Africans searching around with their voices and instruments for harmonics-based intervals from their cultural memory. That searching became an important expressive dimension of the music. Over time, the memory of African tuning systems faded, and the sound of searching across the pitch zone became the sound of the blues. It still sounds good to bend notes until you land on a just intonation interval, though. Try it!

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 a harp 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. To understand why this is, you need to know some music theory, and some history.

The harmonica was designed in central Europe in the 19th century to play the popular music of that time and place. 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).

Sometime between 1870 and 1920, 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, by drawing too hard, it is possible to bend the notes in the E9 chord, making them go flat and thereby producing the blues scale and various blue notes.

Learning to play the blues

The best way to learn to play the blues is from a blues musician. The next best way is to learn from recordings. Listen closely, and see how much you can figure out by ear. Much of the information about the blues in print is limited or simply wrong. The recordings are the most reliable point of reference. Trust your ears.