Mixolydian

The notes

E F♯ G♯ A B C♯ D, then E. It is the fifth mode of A major and shares its three sharps. The D natural in place of D♯ is the single difference from E major.

That one note converts the tonic from a resting chord into a dominant that never leaves. A riff sitting on E7 for sixteen bars is mixolydian by definition, whatever the player calls it.

On the fretboard

Open position covers the scale with the low E as the root, and the twelfth fret repeats it. The overlap with the E blues scale is substantial, which is why players slide between the two without noticing.

The difference that matters is the G♯ — mixolydian has it, the blues scale has G natural. Playing both in the same phrase is the sound of rock guitar, and it is technically a contradiction that nobody minds.

Where it is used

Blues-rock riffs in E, country lead playing over an E7, and any progression that alternates E and D major without reaching A.

In jazz it is the scale over the V of A major, though the guitar meets it far more often in the first role than the second.

It is also the scale behind most country lead playing in E, where the major third and the flattened seventh coexist in the same phrase — the sound that separates country from blues despite the shared harmony.