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Understanding Blues Chords | Dominant Seventh Chords, Degrees and Arpeggios

Hello! In today's harmonica lesson I'll teach you all about blues chords, degrees and arpeggios - what each of these words means and how they can help you with your blues harp playing and soloing.

Basic Chords

What is a chord? It's a set of notes (usually three or more) played together. They form the basis of musical harmony and are the building blocks of songs.

You might have heard the words “one” “four” and “five” chord. These are the three chords used in a 12 bar blues, and the terms (I, IV and V in Roman numerals) just tell you the starting point for each chord. These three chords start on the first, fourth and fifth note (or 'degree') of the scale respectively. Together, they form the classic 12 bar blues format:

In the key of C, we find the I, IV and V by counting through the C scale:


C is the one chord, F is the four and G is the five. The only thing this tells you is the "root" - the note upon which each chord is built.

To show you another example, in the key of G, the I, IV and V chords would be G, C and D because they are taken from the G scale:

G A B C D E F# G

(The key of G will be important later when playing the notes on the harmonica.)

But this doesn’t tell you what other notes are in the chord, so a guitarist/pianist etc would need more information in order to play. Depending on the notes you choose to add, you can make all kinds of chords with different characters (major, minor, diminished, augmented etc).

Seventh Chords

So what type of chords do we use in blues? There’s one specific type of chord that you’ll hear a lot. Blues uses a lot of dominant seventh chords - these are often just called "seventh chords" so the two terms are used interchangeably in the context of blues music.

To build a seventh chord, you combine the root (first note of the scale) with the third and fifth notes of the scale, and then you add a flattened version of the seventh note of the scale (take the seventh note and go down a halfstep).

This is a really "bluesy" chord because it creates tension between the major and minor. That top note (the "flat seventh") creates that tension.

Building Blues Chords

As explained above, to build a seventh chord we take the first degree, third degree, and fifth degree of the scale, plus a flattened version of the seventh degree of the scale.

We're going to look at a blues in the key of G. This is the most common key of blues to play on a C harp. You'll be playing in 2nd position (click here to learn more about positions). The I, IV and V chords would be G, C and D because they are taken from the G scale:

G A B C D E F# G

Now let's build our seventh chords:

To build a G7 chord, we use G, B, D and F.

To build a C7 chord, we use C, E, G and Bb.

To build a D7 chord, we use D, F#, A and C.

Playing Arpeggios

Let’s think about playing these notes on the harmonica. Playing through the notes of a chord in sequence is called playing 'arpeggios'.

Here are the tabs for a C harp:

G7 chord: -2 -3 -4 -5

C7 chord: 1 2 -2 -3/

D7 chord: -1 -2/ -3// 4

Blues Chords Summary

To summarise, here are the most important terms from the lesson:

Dominant seventh chord - chord used in blues containing root, 3, 5, and flat 7.

Seventh chord - shortened name commonly used for dominant seventh chord.

Flat seven - the seventh degree of a scale flattened a halfstep (semitone). Used in a seventh chord to add tension, which is great for blues.

I hope you enjoyed this lesson. Let me know your thoughts in the comments!

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