NOTE: This blog post is in lieu of a short video I posted and then deleted because I wasn’t happy with it. I think the information is layed out more clearly and comprehensively here.
Musicians often bandy around terms like the 1, 4 and 5 chords. And that’s confusing for a lot of people because chords are named after letters, right, not numbers? That’s true, but this very simple bit of music theory can carry you a long way.
Here’s a G major scale:
G A B C D E F# G
How do you know that’s a G major scale? That’s for another day (or you can check my Music Theory For Harmonica Players series). Seven notes and then the octave at the end. What we’re going to do is assign each note in the scale a number, like so.
G A B C D E F# G 1 2 3 4 5 6 7 1
These number are called scale degrees. They mark a notes place in the scale. It doesn’t matter which major scale you’re looking at, the scale degrees stay the same, even though the notes change. Here’s a D scale for example.
D E F# G A B C# D
1 2 3 4 5 6 7 1
See? It’s all about the notes position in the scale, not the notes themselves. Let’s go back to that G major scale.
G A B C D E F# G
1 2 3 4 5 6 7
You can see that the G is marked 1, the C is marked 4 and the D is marked 5. That’s all the 1-4-5 chords are. They are chords built out of those scale degrees.
Incidentally, by convention when we give these Roman rather than Arabic numerals, so it’s I, IV V. I’ll use that from now on.
If we look at the D major scale again we can see that if we were playing in the key of D, our I, IV an V chords would be D, G and A.
A traditional twelve bar blues is just a specific arrangement of the I, IV and V chords. In the diagram below each box represents a bar, and the numeral indicates which chord is played over that bar (a bar by the way, for our purposes is just 4 beats).
If you put a jam track on you should be able to count through the form (1-2-3-4 for each bar) and hear where the band changes chords.
Here’s a good track to use for this.
We don’t tend to play a lot of chords on our harmonica, but we can still play the I-IV-V changes with the band. Here are the notes on a C harmonica.
Now, if we replace those notes with the scale degrees of the G Major scale we get this.
So, when the band is playing the I chord we can play any hole marked 1. When the band is playing the IV chord we can play any hole marked 4. And, you guessed it, when the band is playing the V chord we can play any hole marked 5. (Of course, we don’t have to play those holes, but they are the ones that are the best match for the chord the band is playing).
Try it with a C harp using the jam track above. I recommend using 2 draw, 1 blow and 1 draw to begin with. Then experimenting with the others.
Here’s the very cool thing. The scale degrees don’t change when we change they key of harmonica we’re playing. The notes change but the distances between them don’t. As long as you’re holding the right harmonica the holes and breath direction will always match.
Let’s prove it. Grab your A harmonica and play the same holes along with this backing track.
Pretty cool yeah? That means you don’t have to spend a lot of time memorizing 12 different scale patterns! It’s one of the great advantages of the diatonic harmonica.