Mixolydian

The notes

G A B C D E F, then G. It is the fifth mode of C major and uses only natural notes, which makes it the easiest mixolydian to find: play C major starting from G.

The F natural is the whole difference from G major. One note, and the scale stops leading anywhere — the tonic becomes a place to stay rather than to arrive at.

On the fretboard

Open position covers it entirely with natural notes. The third-fret position with the root on the low E string gives the movable form, and it overlaps with the G major pentatonic most players already know.

The F is the note that must sound. A solo that avoids it plays G major, and the difference is immediately audible over a G7 chord.

Where it is used

Blues and rock over a static G7, and folk tunes that alternate G and F major chords without ever reaching C. Both are mixolydian whether or not anyone says so.

In jazz it is the scale over the V of C major, which makes it one of the first modes learned after dorian — and the one most often played without being named.

For a guitarist it is also the most economical mode to learn: the notes are the same as C major, the shapes are the same as G major, and only the seventh degree has to be remembered differently.