I didn't want to repeat the same notes in the second verse that I used in the first, so I wrote out all the notes of the song and all the notes that were missing in the scale, given that there are twelve notes from octave to octave. All those notes that weren't in the scale were the ones I wanted in for the next verse. The listener isn't aware that they are new notes, but the sound is pleasing to the ear. I change the key, and somehow it's fresh because you haven't heard those notes before.

As quoted in "Paul Simon's Workshop at the Guitar Study Center" by Richard Albero and Fred Styles in Guitar Player (April 1975), p. 21