I - vi - IV - V
Also known as the 50s progression, doo-wop changes, or the “Heart and Soul” chords.
The same four chords as the pop progression, reordered to put the relative minor right after the tonic. That small change gives it a gentler, more circular feel, and it's the sound of close-harmony doo-wop groups and slow-dance ballads from the 1950s on.