Phrygian

The note that defines it

A B♭ C D E F G, then A. It is the third mode of F major and shares its single flat. Compare with A natural minor, which has B natural.

On guitar the B♭ sits at the first fret of the A string, directly above the open root. Alternating those two is the oldest gesture in Spanish guitar music and takes one finger.

On the fretboard

Fifth fret with the root on the low E string, or open position using the A string as the root. The second is where the mode sounds most characteristic, because the open string rings under the semitone above it.

The phrygian dominant — the same scale with C♯ instead of C — is what flamenco actually uses. The plain mode is darker and appears more in metal than in Spanish music.

Where it is used

Metal riffs built on the open A string, and any music that wants menace without a change of key. It also appears over the iii chord in F major, though rarely.

Because A is a resonant key on the guitar, this is the phrygian mode most players learn first — the E version is more common in riffs, but the A version is easier to hear.

The mode is also useful for hearing what a single semitone does. Play A natural minor and A phrygian back to back over the same bass note: only the second degree moves, and the entire emotional register changes with it.