Is Yesterday about Paul's mother?

Paul & Mary McCartney

Paul McCartney has recently suggested a ‘subconscious’ inspiration for the line I said something wrong/Now I long for yesterday was his regret at once chiding his mother for ‘talking posh’:

“Sometimes it’s only in retrospect you can appreciate it. I remember very clearly one day feeling very embarrassed because I embarrassed my mum…We were out in the backyard and … she would talk what we thought was a little bit posh. She said something like ‘Paul, will you ask him if he’s going … I went ‘Arsk! Arsk! It’s ask mum.’ And she got a little bit embarrassed. I remember later thinking ‘God, I wish I’d never said that’

Bereavement

Paul lost his mother when he was fifteen to a cancer that had been kept secret from him. The social convention of the time meant that he was expected to move on swiftly from this trauma. This had a profound and incalculable effect on his life and his art. 

One of these reverberations was a strengthening of his bond with John, who also experienced teenage bereavement.  It may also have been a submerged influence on Yesterday.

Structure

In its lyrical structure, however, Yesterday is clearly a conventional, if enigmatic, song about lost romantic love. The line why she had to go, I don’t know, she wouldn’t say can be taken literally — though it perhaps alludes to the squabbling lovers in We Can Work It Out.