Locrian Mode

Locrian is the seventh mode of the major scale and the most theoretically problematic one. It has a diminished 5th above the root — which means there's no stable perfect fifth to anchor the tonic chord. The tonic chord built from Locrian is a half-diminished chord (m7♭5), which by nature sounds unresolved. Locrian is hard to use melodically as a tonal centre because it refuses to feel like home.

Construction

The seventh mode of the major scale — starts on the 7th degree.
B Locrian = C major scale starting on B:
B C D E F G A B

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

Everything is flat except the 4th. The ♭2 creates the same half-step tension as Phrygian. The ♭5 is the unique feature — the diminished fifth above the root makes the scale inherently unstable.

Key Scales

B Locrian: B C D E F G A B
E Locrian: E F G A B♭ C D E
A Locrian: A B♭ C D E♭ F G A
D Locrian: D E♭ F G A♭ B♭ C D

Sound and Character

Dark, unstable, tense. The diminished fifth above the root means the chord built on the tonic has nowhere stable to land. It sounds like unresolved tension without a release. This is exactly what makes it useful in certain contexts — it can maintain harmonic tension indefinitely without resolving, which has appeal in horror soundtracks, avant-garde jazz, and extreme metal.

Practical Use: The Half-Diminished Chord

The main practical use of Locrian is over half-diminished (m7♭5) chords in jazz — specifically the ii chord in a minor ii-V-i progression:

Minor ii-V-i in A minor:
Bm7♭5 — E7 — Am

Over Bm7♭5: B Locrian works.
All notes of Bm7♭5 (B D F A) are in B Locrian.

Many jazz players prefer Locrian #2 (Locrian with a natural 2nd, which is the 6th mode of melodic minor) over a half-diminished chord because the natural 2nd avoids the harshest tension of regular Locrian. But standard Locrian is correct theoretically and works in practice.

Locrian in Metal

Some metal guitarists use Locrian for its unresolved tension — riffs that sit on the flat-5 relationship or use the ♭2 for a more extreme dark sound than Phrygian. It's not common as a sustained tonal centre even in metal, but short riffs and passages in Locrian work well when sustained instability is the goal.