Lead-in — how players set it up4 souring to 4- is the standard on-ramp (IV → iv → bVII⁷).Straight off 1Δ7 — the 4-⁷ is the mood swing itself.Or from plain 4: major first, then borrowed, then backdoor.Follow — where it usually goesLands on 1Δ7 with zero hangover — often straight into a new section.Tag it: 1Δ7 to 6-⁷ keeps the afterglow moving.Or take the backdoor at its word and stay up a minor 3rd.
Ride the key's b7 and b3 over the b7⁷ — backdoor melody is blues vocabulary landing on a major porch.Target tones (in C)Fm7 — lean on Ab (b3) · Eb (b7)Bb7 — lean on D (3) · Ab (b7)Cmaj7 — lean on E (3) · B (7)Half-step wiresEb ↘ D · Bb → B · F ↘ E