The Key of Ab at the Electric Bass Seat

Called in Ab, a tune has Ab – Bbm – Cm – Db – Eb – Fm – G° available to it before anybody substitutes anything; the parallel minor, G# minor, offers G#m – A#° – B – C#m – D#m – E – F# instead. The two-five-one that closes most choruses is built out of three of those seven.

The electric bass seat carries the amplified bottom — the same harmonic duty as the upright, played with a fingerboard that answers back and a sustain the room can hear over a backbeat. The chord tones are the same ones the upright would choose; what changes is that a note can be held through the bar instead of dying, so a line can lean on a chord rather than announce it.

Learn where the ii, the V and the I fall in Ab until the hand goes there without asking, and the substitution rules become edits to something you already know rather than new material.