Lydian

The note that defines it

E F♯ G♯ A♯ B C♯ D♯, then E. It is the fourth mode of B major. Against E major, which has A natural, the raised fourth is the single difference.

The A♯ sits a tritone above the tonic. Because the open low E can drone underneath, the interval is unusually easy to hear here — the mode explains itself on this instrument better than on most.

On the fretboard

Twelfth fret with the root on the low E, or open position using the low string as a drone. The second is where the mode sounds most characteristic.

The trap is the open A string, which does not belong to the scale. Guitarists used to E major reach for it constantly, and every time the lydian sound collapses.

Where it is used

Instrumental rock and film music over an Emaj7 chord, and in progressive playing where a static major chord needs a scale that will not resolve.

It also appears in songs that alternate E and F♯ major — the second chord contains the A♯, and the mode follows from the progression rather than being chosen.

It is also one of the few modes where the guitar can hold a drone and play the defining note at once: the open low E rings while the A♯ is fretted above it, and the tritone is audible without any harmonic support.