The last major mode is locrian. This scale is used over minor seven flat five or half diminished chords. In jazz, this chord functions as a ii chord in a minor ii/V i. It can also function as a substitution for a V chord; you see this VERY rarely outside of Romantic era classical music, but I’m sure someone out there could find a Steely Dan tune where it happens. Let’s take a C-7b5 chord: C Eb Gb Bb. You’ll notice that this chord has, surprise, a flat five in it, and locrian is the only choice of major modes that has a flatted fifth note.
C locrian is: C Db Eb F Gb Ab Bb C, and again you have three choices of major pentatonics that fit into this scale. The first is Ab major pent: Ab Bb C Eb F. Again, the flat 6th, in this case, Ab, is a handle with care note, as landing on it too much will start to make the chord sound like an Ab7; the rest of the notes are legal and fun. The second choice is Db major pent: Db Eb F Ab Bb, which gives you some nice tension, as it’s a half step away from the root. The most locrian choice is the third: Gb major pent: Gb Ab Bb Db Eb. This scale gets both the flat five and the flat second, which are the main notes that make locrian sound like locrian.
When I’m using this method and soloing, I usually go straight to the Gb major pent, as most minor seven flat 5 chords don’t last that long in the songs they’re in. The other scales offer some nice resolutions too though, which I’ll get into when I get some time to write about melodic minor modes.
Next up, we’ll look at using this with II V I progressions.