Prince, Purple Rain (1984)
The opening progression of Purple Rain — Bb, F, Gm, Eb — moves with a slow, ceremonial gravity that feels inevitable from the first struck chord. Bb resolves warmly into F before the minor colour of Gm introduces a gentle ache, and the Eb brings the phrase to a spacious, open close, ready to loop back and begin again. That shift into the relative minor and out again is what gives the sequence its emotional complexity: neither purely joyful nor despairing, but suspended somewhere between the two. For guitarists and keyboardists alike, playing those changes is quietly satisfying, the harmony doing more expressive work than its simplicity suggests. A landmark of mid-eighties R&B and rock balladry, the song remains one of Prince's most enduring achievements.