B♭ Mode 4 Scale
B♭ Mode 4 contains 8 notes: B♭, B, C, E♭, E, F, G♭, A. It has 3 flats: B♭, E♭, G♭. The step pattern is H–H–W+H–H–H–H–W+H–H.
Messiaen Mode 4 is an 8-note scale with 6 possible transpositions. Its pattern of three semitones followed by a minor 3rd creates a distinctive angular quality.
The formula is 1, b2, 2, 4, b5, 5, b6, 7. The octave divides into groups of 1-1-3-1 semitones, repeated. With 6 transpositions, it is less "limited" than modes 1-3 but still symmetrical. The cluster of consecutive semitones followed by a wide gap creates a push-pull tension that Messiaen used for passages requiring angular, unpredictable melodic movement.
The alternation between tight chromatic clusters and wide leaps translates well to guitar — use the clusters on a single string and the leaps as cross-string jumps. Less commonly used than modes 2 and 3, but valuable for breaking out of diatonic habits.