This classic 12-bar blues progression follows a timeless and instantly recognisable form, built around dominant 7th chords throughout. It begins by sitting firmly on the I7 chord for the first four bars, creating a strong tonal centre, before moving to the IV7 in bars 5 and 6 for the familiar subdominant lift. The sequence then returns to I7 in bars 7 and 8, rises to V7 in bar 9 for added tension, drops to IV7 in bar 10, resolves to I7 in bar 11, and finishes on V7 in bar 12 for the traditional turnaround that leads naturally back to the top.