Stop 6 of 6
Open seventh chords
A7, D7, E7 and B7: the colour of the blues.
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Stop 6 of 6
A7, D7, E7 and B7: the colour of the blues.
You've got the blues form and its sway. What's missing is its colour. Play an A and then an A7: one finger apart, the chord goes from "bright and round" to "tastes like the blues". That finger adds the minor seventh, and the resulting chord, the , is the harmonic signature of the blues. At this stop you learn the four open shapes you'll use most and drop them into the 12-bar blues.
Listen to A first and then A7. They're nearly identical: only one note changes.
The second sounds less "finished", with a little tension, as if it wanted to go somewhere. But it isn't ugly or sad: it sounds like the blues, like a bar with the door wide open. Play it yourself: make an A and lift the finger off the 3rd string. That open string is G, the seventh.
A major chord has three different notes: root (1), third (3) and fifth (5). The dominant seventh chord adds a fourth one: the minor seventh, written ♭7. Its formula is 1 3 5 b7.
Where is that seventh? It's the note one whole step (two frets) below the root an octave up. In A, a whole step below A is G.
String 5, Open: A2 · 1 · Scale tone
Look at the diagrams with degrees instead of fingers. The spot marked b7 is the one that brings the colour:
In classical music this kind of chord almost always appears on the fifth note of the scale, the V, which theory calls the dominant: hence dominant seventh. It contains two notes, the third and the seventh (in A7, C♯ and G), a apart, the most unstable distance in music. That clash wants to resolve, and in classical music the V7 almost always moves to the I.
The blues breaks that rule: it uses the seventh chord on the I, the IV and the V, and often never resolves it. The tension stops being a problem to solve and becomes the colour of the style. You'll go deeper into this in Harmony City.
These are the shapes you need to play blues in A and in E. The numbers in the circles are fingers.
Two widely used alternative shapes put the seventh on a higher string, where it's easier to hear:
In the first, finger 1 presses strings 4, 3 and 2 at fret 2 at once and the pinky adds G on the 1st string. In the second, you play a normal E and add the pinky at fret 3 of the 2nd string (D). Use them when you want the seventh to "sing" more; the basic shapes are still the most comfortable for quick changes.
Blues melodies lean heavily on two notes that are "bent" compared to the major scale: the minor third and the minor seventh. They're the . Putting the minor seventh inside the chords puts the harmony on the melody's side: guitar and voice speak the same language.
Look at this detail of the blues in A, too:
| Chord | Notes | Its seventh | What that note is in A |
|---|---|---|---|
| A7 (I7) | A C♯ E G | G | the minor seventh of A: a blue note |
| D7 (IV7) | D F♯ A C | C | the minor third of A: another blue note! |
| E7 (V7) | E G♯ B D | D | the root of the IV: it pushes towards it |
When D7 sounds, a C appears, deliberately rubbing against the C♯ of A7. That friction between major third and minor third is the heart of the blues sound.
Changing chords on time matters more than perfect shapes. Two key changes:
Strum with a shuffle: the hand moves in triplets, striking on the number and on the "let".
At the shuffle stop you saw a boogie variant that adds the seventh: 5-6-b7-6. Now you know where that note comes from: on A7 it's G, fret 5 of the 4th string. You need to stretch the pinky three frets from finger 1; if you can't reach yet, lower the tempo and let your hand open up gradually.
Goal: Make at least 30 clean changes in one minute between A7 and D7, and 25 between E7 and B7.
Strum the shuffle pattern from the previous scene. First without the quick change, then with it (bar 2 on D7).
Goal: Play two full rounds in A with a shuffle strum, changing each chord on time on beat 1.
If B7 doesn't land on time yet, play a B5 (x244xx) instead and go back to B7 when you're ready.
Goal: Play two rounds in E without stopping, including the change to B7 in bars 9 and 12.
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