Dominant 7th chord
R 3 5 b7. A7 = A C# E G. A blues in A uses three of them.
- Root
- 3rd
- 5th
- b7
- Scale
| Formula | In A |
|---|---|
| R 3 5 b7 | A7 = A C# E G |
On the guitar. Open A7, barre A7 at fret 5, and the arpeggio inside pentatonic box 1.
Drill. Play the arpeggio of A7, D7 and E7 in one position, slowly.
The core idea to revise
A blues in A uses three dominant 7th chords (A7, D7, E7). No single major or minor key contains all three. That is why blues breaks the “stay in key” rule, and why the minor pentatonic works: its b3 (C) rubs against the chord’s major 3rd (C#). Bending C up to C# resolves the rub. That rub and release is the blues sound.