Originally conceived as an instrumental tune, ‘Summer’s Day Song’ only received vocals after a rough mix had been made and it was selected for inclusion on the original double album version of McCartney II.
I had heard a piece of music that I liked, which was a very classical sounding piece. So, that day, when I went into the studio, I thought it would be a nice change if I tried something, sort of, classical. I built it up, wrote a couple of words, and put a few vocals over the top, so it does sound like something classical-cum-something else.
The instrumentation relies heavily on the Mellotron’s flute setting, which had been used by The Beatles in 1967 for the introduction to ‘Strawberry Fields Forever’. The rest of the song, however, owed little to 1960s psychedelic excesses, and was instead an exercise in restrained musical arrangement.