Bb Locrian Mode on the Keyboard: Five Black Keys and Two White
Play a Bb natural minor scale, then change just two notes: lower the second note from C to Cb, and lower the fifth from F to Fb. That small edit turns a familiar, moody minor sound into something far stranger. The result is the Bb Locrian mode, a scale that seems to lean forward and never quite land. It's the darkest of the seven classic modes, and once you hear why, you'll recognise its tension everywhere.
A Scale You Can See on the Black Keys
Sit at a piano and find Bb, the black key just left of B. Now play every black key from there upward: Bb, Db, Eb, Gb, Ab. Add only two white keys, B and E, and you have the whole of Bb Locrian. Written out properly, the notes are Bb, Cb, Db, Eb, Fb, Gb, Ab.
That's a lovely shape to see under your hands. The five black keys form the backbone, and the two white keys sit in the gaps where black keys don't exist.
Why B is called Cb and E is called Fb
Here's the part that looks odd at first. The white key B is written as Cb, and the white key E is written as Fb. That's not a trick. Scales like this use each letter name once, A through G, in order. Since Bb already uses the letter B, the next note has to be some kind of C. The key one step above Bb is the white B key, so its name in this scale is Cb. The same logic makes E into Fb, because Eb already claimed the letter E.
So the spelling follows a simple rule: one of each letter, no letter skipped and none repeated.
Where the Half Steps Fall
A whole step is a jump of two piano keys, skipping one in between. A half step is the smallest step in Western music, from one key to the very next with nothing between. Locrian follows this pattern: H - W - W - H - W - W - W.
On the keyboard you can watch it happen. From Bb up to Cb (the white B) is a half step, right next door. Then two whole steps take you through Db to Eb. From Eb to Fb (the white E) is the second half step. Finally three whole steps climb through Gb and Ab back to Bb.
Notice where that first half step sits: right at the bottom, squeezed against the root. That crowding is a big part of the mode's uneasy feel. The root has a note pressing on it from just above, so it never feels spacious or settled.
The Note That Changes Everything: Fb
Locrian's formula is 1, b2, b3, 4, b5, b6, b7. Each number is the note's distance from the root, and the "b" means lowered by a half step compared with a major scale. The one that defines Locrian is the b5, the flattened fifth. In this key, that's Fb.
Most scales have a perfect fifth, which in Bb would be F. That interval is the solid floor under nearly every chord we hear as stable. Locrian pulls the floor away. Play Bb and Fb together on the piano and listen: it's the tritone, a restless, buzzing interval that wants to move. Then play Bb and F for comparison. The difference is instant.
Because of that Fb, the chord built on the root is Bbdim (Bb-Db-Fb), a diminished triad. Diminished chords sound tense by nature, so your home chord is itself unstable. That's the whole personality of Locrian in one sentence.
Family Ties and the Easier Spelling
Bb Locrian uses exactly the same notes as Cb major (Cb, Db, Eb, Fb, Gb, Ab, Bb), whose key signature has 7 flats. A key signature is the group of sharps or flats written at the start of the music so you don't have to mark them on every note. The only difference is which note you treat as home: Cb major settles on Cb, while Bb Locrian keeps circling back to Bb.
Seven flats is a lot to read, and honestly, most musicians don't write it this way. The usual spelling is A# Locrian, with a key signature of 5 sharps. It sounds exactly the same, played on the very same piano keys. So if you come across A# Locrian in a book or chart, relax: it's the same sound in different clothes.
The Chords It Makes, and One to Try
Stack every other note of the scale and you get these chords:
- i°: Bbdim (Bb-Db-Fb) / Bbm7b5
- bII: Cb (Cb-Eb-Gb) / Cbmaj7
- biii: Dbm (Db-Fb-Ab) / Dbm7
- iv: Ebm (Eb-Gb-Bb) / Ebm7
- bV: Fb (Fb-Ab-Cb) / Fbmaj7
- bVI: Gb (Gb-Bb-Db) / Gb7
- bvii: Abm (Ab-Cb-Eb) / Abm7
The four-note version of the home chord, Bbm7b5, is often called "half-diminished." Jazz players reach for the Locrian sound over exactly this kind of chord.
To keep Bb feeling like home despite its instability, hold a low Bb in the bass and try: Bbm7b5 – Cbmaj7 – Abm7 – Bbm7b5. The move from Bbm7b5 up to Cbmaj7 and back is pure Locrian, that half step rubbing right against the root. Producers and metal players love this kind of half-step grind for dark, menacing textures.
How a Melody Moves Here
Melodies in Locrian rarely rest. Fb tends to sink down to Eb, and Cb leans hard toward Bb. Singers will feel this immediately: try humming Bb, Cb, Bb, then Bb, Fb, Eb. The first gives a brooding, hovering feel; the second has a slip-and-fall quality.
Good Locrian lines often hover around the root without making a big statement of arrival. Short phrases, repeated notes and half-step sighs work far better than soaring leaps.
For guitarists
On a standard-tuned guitar, your Bb root sits on the low E string at frets 6 and 18, and on the A string at frets 1 and 13. The 1st-fret A-string root is handy for heavy riffs: chug the open low register around it and slide up a half step to the 2nd fret for that Cb crunch.
Something to Try Tonight
At the piano, hold Bb low with your left hand. With your right, play only the black keys in any order you like for a minute. Then let your right hand drift onto the white E, the Fb, and land back on Bb. Listen for the moment the sound turns from merely dark to genuinely uneasy. That shift is Locrian.
For the bigger picture, read The Locrian Mode.