Blues Harmonica Music Theory

Last I touched upon some arguments about music theory. This week I will give you a quick primer of the blues harmonica music theory you need to know to become an even better player. As you will see it is not very complicated and the benefits are well worth it.

Structure and chords of the 12 bar blues

The most common form of accompaniment you will come across when playing blues is the 12 bar blues. The picture shows the 12 bar blues outline with roman numerals and writing it like this means it can be used in any key.

Blues Harmonica Music Theory 12 bar blues outline

12 bar blues outline in roman numerals

  • I is the tonic chord of the key, based on the first note of the scale
  • IV is the sub-dominant chord of the key, based on the fourth note of the scale
  • V is the dominant chord of the key based on the fifth note of the scale

More on chords

A chord is two or more tones played together taken from a scale and the chords in a major key are based on the tones of the major diatonic scale. A G-chord is made up of notes from the G-major scale, a C-chord is made up of notes from the C-major scale and a D-chord is made up of notes from the D-major scale. What is often referred to as a chord is the first, third and fifth note of the scale played together. Stacking every second not of the scale is usually how it’s done (we won’t dive super deep into this). There is one exception however and that is that the seventh note of the scale i flattened when it is included in a chord. This makes the chord sound more interesting.

For the key of G (second position on a C harmonica) these are the chords:

  • I is G (found on a holes 1-3 draw on a C-harmonica)
  • IV is C (found on a holes 1-3, 4-6, 7-9 exhale on a C-harmonica)
  • V is D (not found as a complete chord on a C-harmonica, root note on 1, 4, 8)

Chord tones

To be able to use the knowledge of the chords further, it is a good idea to know where to find the chord tones on the harmonica. This blues harmonica music theory knowledge is second position specific and carries over when you change key as you then change the harmonica as well to stay in second position. Knowing the chord tones is especially important for the V-chord as few of the chord tones are in the blues scale (covered below). For each chord the cord tones are (key of G, although best to think of them as root, third, fifth and flat seventh):

  • I-chord G, B, D, F (root, third, fifth and flat seventh)
  • IV-chord C, E, G, Bb
  • V-chord D, F#, A, C

For the I-chord (read about harmonica tabs here):

  • G (root note) 2, 3+, 6+, 9+
  • B (third) 3, 7, (10+’)
  • D (fifth) 1, 4, 8
  • F (flat seventh) 2”, 5, 9

For the IV-chord:

  • C 1+, 4+, 7+, 10+
  • E 2+, 5+, 8+
  • G 2, 3+, 6+, 9+
  • Bb 3′, (6+o (overblow)), (10+”)

For the V-chord:

  • D 1, 4, 8
  • F# 2′, (5+o (overblow)), (9+’)
  • A 3”, 6, 10
  • C 1+, 4+, 7+, 10+

The notes on parenthesis are overblows and blow bends and if you do not master those techniques just ignore them.

Blues scale

The blues scale is probably the most common piece of practical blues harmonica music theory that people do learn. It gives a safe path to a bluesy sound over the 12-bar blues. The blues scale is based on the I-chord and the minor pentatonic scale connected to that chord. In addition to that scale the minor fifth is added which is a note that creates a lot of tension. It is known as tritone or “the Devil’s Interval”. The blues scale is made up of the following scale degrees:

Root, minor third, fourth, minor fifth, fifth, minor seventh


R, b3, 4, b5, 5, b7

On the harmonica this translates to:

1+, 1′, 1, 2”, 2, 3′, 4+, 4′, 4, 5, 6+, (6′, 6,) 7+, 8, 9, 9+’, 9+, 10+”, 10+
4, b5, 5, b7, R, b3, 4, b5, 5, b7, R, (b2, 2,) 4, 5, b7, R, b3, 4

Note: The holes and tones in parentesis are often added to make the scale more flowing as the b3 and b5 are missing between holes 6 and 9. This adds a little extra bluesiness to this range.

To make it a little bit more readable, here is the scale between holes 2 and 6.

2, 3′, 4+, 4′, 4, 5, 6+
R, b3, 4, b5, 5, b7, R

Blue notes

Blue notes are notes that create nice bluesy tension towards the chord. These are b3, b5 and b7. The blues scale contain these notes for the I-chord but also knowing them for the IV-chord and V-chord gives you nice option to play over those chords.

For the I-chord:

  • b3 3′, (6+o (overblow)), (10+”)
  • b5 1′, 4′
  • b7 2”, 5, 9

For the IV-chord:

  • b3 8+’
  • b5 2′, (5+o (overblow)), (9+’)
  • b7 3′, (6+o (overblow)), (10+”)

For the V-chord:

  • b3 2”, 5′, 9
  • b5 3”’, 6′
  • b7 1+, 4+, 7+, 10+

Benefits of blues harmonica music theory for soloing

Playing solos that completely stay within is absolutely fine but using chord tones and blue notes to follow the chords and mark chord changes for example can really create awesome solos. Especially how you handle to V-chord can set you apart from the rest of the pack. Here knowing the chord tones is cruical.

Benefits of blues harmonica music theory for accompaniment playing

When playing accompaniment playing you have a few options on what to play. However you chose to play it is your job to play something that is musically appropriate. You can for example play a bass line together with the bass player and then you will definately need to know where the chord tones are. Another option is to create tension against the chords and then you need to use blue notes and stay away from the chord tones. However you chose to play, know the theory will help you.

Putting it to use

I hope I have convinced you that learning blues harmonica music theory is a good thing and you want to make use of it. What you need to do now is take each of the concepts in this article, comit it to memory and start using it. The best way to do this is to concentrate on one single thing and have that as a focus when practicing playing solos for example. If you want to get to know the chord tones then play a lot of solos just using chord tones, when that starts becoming natural start using a few blue notes and so on. Before you know it this will become second nature.

Should you want to learn more general music theory I can recommend “Music Theory for Dummies” as a good starting point or you can take music theory classes on Skillshare (take advantage of the Premium membership offer).

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