Dorian

The notes

A B C D E F♯ G, then A. It is the second mode of G major, sharing that key’s single sharp. Play G major starting from A and the scale appears without learning anything new.

The F♯ is everything. A natural minor has F, and the difference between the two scales is one semitone in one place — yet a listener hears them as different colours entirely.

On the fretboard

The fifth-fret position with the root on the low E string is standard, and it overlaps with the A minor pentatonic that most players already know. Adding the B and the F♯ to that box converts it to dorian.

Open position also works, because A, B, D, E and G are available open or nearly so. That accessibility is part of why the mode appears so often in guitar-written music.

Where it is used

Modal rock and folk: a riff over Am with a D major chord in it is dorian, because that D contains the F♯. Countless songs use this without naming it.

In jazz it is the default scale over a minor seventh chord functioning as a tonic, which makes it one of the first modes any improviser learns after the pentatonics.

The mode is also the reason so many guitar riffs in A avoid the F entirely: leave it out and the passage sits between minor and major, which is exactly where a great deal of rock wants to be.