Lydian Mode

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

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

Compare to F major (Ionian): F G A B♭ C D E F
The B is natural in Lydian (B♭ in Ionian) — the raised 4th is the difference.
The raised 4th creates a tritone above the root (F to B = 6 semitones = tritone).

Lydian in Common Keys

Lydian root	Notes	Parent major key	The #4
C Lydian	C D E F# G A B	G major	F#
G Lydian	G A B C# D E F#	D major	C#
D Lydian	D E F# G# A B C#	A major	G#
F Lydian	F G A B C D E	C major	B
B♭ Lydian	B♭ C D E F G A	F major	E
E♭ Lydian	E♭ F G A B♭ C D	B♭ major	A

Sound and Character

Bright but floating — major without the resolution. The raised fourth removes the strong subdominant pull that Ionian has and replaces it with a tritone against the root, creating ambiguity. The result sounds major in quality but harmonically unmoored in a pleasant way — like being in a key but not quite touching the ground.

The II Chord — Unique to Lydian

In F Lydian, the diatonic chords include:
  I    = Fmaj7   (tonic)
  II   = G major  ← a major chord a whole step above the tonic
  iii  = Am7
  #iv° = Bø (half-diminished)
  V    = Cmaj7   (not dominant! — no dominant 7th in Lydian)
  vi   = Dm7
  vii  = Em7

The II chord (G major over F Lydian) is the Lydian signature.
The Imaj7 → II move is the sound of Lydian.

Note: Lydian has no dominant 7th chord. The 5th degree chord (Cmaj7)
is a major 7th, not a dominant 7th. This means Lydian feels harmonically
suspended — there's no strong dominant pull back to the tonic.

Lydian vs. Ionian Over Major Chords

In jazz, Lydian is often preferred over Ionian for tonic major chords. The natural 4th in Ionian (F in C Ionian) can clash with the major 3rd (E) in a Cmaj7 voicing. In C Lydian, the 4th is raised to F# — the #11 — which is an available and usable extension that adds colour without clash:

C Ionian: C D E F G A B  ← F (natural 4th / 11th) can clash with maj7 voicing
C Lydian: C D E F# G A B ← F# (#11) adds lifting colour, no clash

George Russell's Lydian Chromatic Concept argues that Lydian is the
"natural" major scale in terms of acoustics — the overtone series
above a tone produces a Lydian-like collection.

Lydian in Film Scores

Film composers use Lydian for floating, magical, or supernatural sequences precisely because it sounds major (positive, bright) but unresolved (suspended, hovering). The audience feels something positive but mysterious:

John Williams — "Flying" theme from E.T., opening of Star Wars (various cues)
Danny Elfman — The Simpsons theme (the opening is Lydian)
Joe Hisaishi — much of the Studio Ghibli film music uses Lydian for wonder sequences
Howard Shore — The Shire theme (Lord of the Rings) has Lydian sections

References

Levine — The Jazz Theory Book
Russell — Lydian Chromatic Concept of Tonal Organization
jazzguitar.be — Lydian Mode ↗