Lydian Mode

Lydian is a major mode with a raised fourth degree. That single alteration transforms the familiar major scale into something otherworldly and floating — dreamlike rather than grounded. It's the sound of film scores, ambient music, and the more ethereal moments in jazz. Joe Satriani named an album after it. John Williams uses it constantly.

Construction

The fourth mode of the major scale — starts on the 4th degree.
F Lydian = C major scale starting on F:
F G A B C D E F

Formula: 1  2  3  #4  5  6  7
Step pattern: W - W - W - H - W - W - H

Compared to the major scale (Ionian), Lydian raises the 4th degree by a half step. In F Lydian that's a B natural instead of B♭. This augmented 4th (the tritone above the root) is the defining note.

Key Scales

F Lydian:  F G A B C D E F
C Lydian:  C D E F# G A B C
G Lydian:  G A B C# D E F# G
D Lydian:  D E F# G# A B C# D

Sound and Character

Bright but floating — major without the resolution. The raised fourth removes the IV chord (one of the strongest gravitational pulls in tonal music) and replaces the whole-step above the 3rd with a tritone, creating ambiguity. The result is major quality without the feeling of closure. It's harmonically unmoored in a pleasant way.

The Lydian sound is all over The Simpsons theme (Danny Elfman), John Williams's work ("Flying" from E.T., the main Star Wars theme entering a new key area), and Steve Vai's guitar work. In jazz, the Lydian dominant scale (Lydian with a flatted 7th) is more common — see the Lydian Dominant article.

The #4 Chord

Built on the #4 of Lydian is a major chord:
F Lydian: Imaj7=Fmaj7, II=G major, iii=Am, #iv°=Bø, V=Cmaj7, vi=Dm7, vii=Em7

The II chord (major) is uniquely Lydian — a major chord a whole step above the tonic.
The Fmaj7 → G move (I → II) is the Lydian sound.

Where to Use It

Over Imaj7 and maj7#11 chords. In jazz, Lydian is often the preferred choice over Ionian for tonic major chords precisely because the #4 avoids the natural 4th's tendency to create tension against a maj7 voicing. Over a Cmaj7 chord, C Lydian gives you a richer sound than C Ionian with no notes that clash. This is the basis of George Russell's Lydian Chromatic Concept — an influential theoretical framework for jazz improvisation built on Lydian as the fundamental scale.