The tonic key of the song is F major (although, since McCartney tuned his guitar down a whole step, he was playing the chords as if it were in G), where the song begins before veering off into the key of D minor. It is this frequent use of the minor, and the ii-V7 chord progression (Em and A7 chords in this case) leading into it, that gives the song its melancholy aura. The A7 chord is an example of a secondary dominant, specifically a V/vi chord. The G7 chord in the bridge is another secondary dominant, in this case a V/V chord, but rather than resolve it to the expected chord, as with the A7 to Dm in the verse, McCartney instead follows it with the IV chord, a B. This motion creates a descending chromatic line of C–B–B–A to accompany the title lyric.