A dominant 7 a half step above the 5 chord shoves it from behind — the whole grip slides down one fret. Classical theory knows this sound as the German augmented sixth wearing jazz clothes.
hear it in Schubert everywhere · gospel reharmonizations
Lead-in — how players set it up4 or 4- ahead of it makes the chromatic slide obvious.From 1⁷ heading to 4 — then the b6⁷ shoulder-checks.Or from 4- for maximum borrowed darkness before the push.Follow — where it usually goes5⁷ lands with extra momentum — cadence immediately.Cadence immediately — the momentum won't keep.Or hear b6⁷ as its German twin — the respelled hinge opens onto 5⁷.
Over the b6⁷, the key's b6 and 4 (its b7) both fall by half step into the 5 chord — a two-wire descent.Target tones (in C)F — lean on A (3)Ab7 — lean on C (3) · Gb (b7)G7 — lean on B (3) · F (b7)C — lean on E (3)Half-step wiresF → Gb · A ↘ Ab · Ab ↘ G · C ↘ B · B → C · F ↘ E