music writers covach and boone describe the riff as blues-derived, which uses a minor blues pentatonic scale with an added flattened fifth note (or common blues scale). the song follows a blues chord progression (i–iv–i) during the first eight bars. brown had a difficult time writing lyrics that fit the riff. after an all-night session, bruce played it on a standup bass while lyricist pete brown was staring out the window. slowly, he started to write "it's getting near dawn and lights close their tired eyes", which is used in the first verse. later, to break up the rhythm, clapton wrote a refrain which also yielded the song's title. it consists of eight-bar sections using three chords, when the key shifts to the v chord (i = v):