A Mixolydian
The dominant sound, in the key where rock actually lives.
A Mixolydian is the major scale with a flat 7th, built on A. If a riff sounds major but bluesy and never quite resolves, this is usually the reason.
Major with a ♭7
A Mixolydian is A B C# D E F# G. The major 3rd (C#) keeps it bright; the ♭7 (G natural, not G#) is what takes away the pull toward the tonic and leaves it hanging.
- The major 3 (C#) means it is not a minor scale.
- The ♭7 (G) is the one note that separates it from A major.
- It is the scale that matches an A7 chord exactly.
Why so many riffs are here
Over an A7 or A5 vamp, this scale gives you the major 3rd for brightness and the ♭7 for grit. Mix it with A minor pentatonic and you get the major/minor blur that most rock lead playing is built on.
- It matches an A7 chord note for note.
- Combine it with A minor pentatonic for the classic rock blend.
- The A string open gives you a free root to drone against.
Static, not moving
Mixolydian needs a chord that stays put. An A–G–D vamp is the giveaway: that G major chord contains G natural, which only exists in A Mixolydian, not in A major.
- A–G–D is a Mixolydian progression, not a major-key one.
- The ♭VII chord (G) is the Mixolydian signature.
- Static dominant vamps beat fast key changes.
Flatten one note of A major and you get the scale that half of rock and all of funk is written in.
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