Locrian nat2

Locrian with a natural second

The Locrian mode is 1 ♭2 ♭3 4 ♭5 ♭6 ♭7 — everything lowered that can be lowered, including the fifth. Restore the second to its natural form and one semitone cluster disappears from the bottom of the scale, which changes how it behaves far more than a single note usually would.

The diminished fifth stays, so the tonic chord is still half-diminished and still cannot rest. What changes is the ninth: Locrian gives a half-diminished chord a flat ninth, an interval that clashes with the root and that most players avoid. Locrian ♮2 gives it a natural ninth, which is a usable extension.

That is the practical reason the mode exists as a separate entry rather than a curiosity. A chord tone that could not be used becomes one that can, and half-diminished chords are common enough for that to matter every time one appears.

The half-diminished scale

Jazz method books frequently call this the half-diminished scale, and the name is more informative than the modal one. Half-diminished chords — m7♭5 — open almost every minor two-five-one, so a scale that covers them properly gets used constantly, whatever it is called.

In a minor two-five-one in A minor the chords are Bm7♭5, E7alt, Am. Over the Bm7♭5, Locrian ♮2 is the default choice: from B it is B C♯ D E F G A, which is C melodic minor counted from the sixth degree. The shortcut on the instrument is the same as for the rest of this family — play melodic minor a minor third above the chord root.

Compare with plain Locrian on the same chord and the difference is audible in one note. The C♯ sits comfortably as a ninth; a C natural sits a semitone above the root and fights it. Most players who think they are playing Locrian over m7♭5 are in fact avoiding that note, which is to say they are playing this mode without naming it.

Against Locrian ♮6 from harmonic minor

Two modes in this catalogue cover half-diminished chords, and they differ by one degree. Locrian ♮2 comes from melodic minor and restores the second. Locrian ♮6 comes from harmonic minor and restores the sixth instead, leaving the flat second in place.

Jazz chooses this one far more often, and the reason is the same as above: the second degree becomes a usable ninth, whereas the sixth degree is a thirteenth, which matters less on a chord that rarely extends that far. Locrian ♮6 belongs where the surrounding harmony leans on harmonic minor — where the following dominant carries a leading tone rather than a full set of alterations.

In practice that maps onto a simple choice. If the two-five-one is heading toward a plain minor chord with a classical cadence, harmonic minor and its second mode fit the whole progression. If the dominant is altered, melodic minor covers both the m7♭5 and the altered dominant with one set of notes shifted by a step, and this is the mode that starts it.

Frequently asked questions