FA-81190 / Music interval and transposition theory / Member archive

Roman numeral label for a chord in a key: flat prefix attached to the degree below · case 05

The borrowed flat-six chord in C major is labelled bV instead of bVI.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Input [tonic_pc, mode, root_pc, quality] with mode major or minor (natural minor scale 0 2 3 5 7 8 10) and quality maj, min, dim or aug. Diatonic roots use their degree; in minor the leading tone (11 semitones) is degree VII with no prefix. Other roots in major are written b + the degree a semitone above; in minor # + the degree a semitone below. Numerals are uppercase for maj and aug, lowercase for min and dim, with suffix ° for dim and + for aug. Invalid input returns None.

Why this case matters

Harmonic analysis and ear-training tools label chords relative to the key.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
oracle 0	`"bVI"`	`"bVII"`	Failed

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