John and Yoko were staying together at Ringo’s house in March of 1969. It’s there that John wrote “Because,” inspired by Beethoven, as played by his wife.
“Yoko was playing `Moonlight Sonata’ on the piano,” Lennon said to Peter Scheff. “She was classically trained. I said, ‘Can you play those chords backward?’ and wrote ‘Because’ around them. The lyrics speak for themselves; they’re clear. No bullshit. No imagery, no obscure references.”
When I interviewed Yoko in 1992, I asked her about her memories of the origins of “Because.”
“When you really listen to it, ” she said, “you see that he did play the chords backwards at one point but I think eventually it cleaned up a bit into a pop format. So he didn’t use all the chords. But that was the initial inspiration.”
Source: americansongwriter.com