McCartney talks chords and more in latest "You Gave Me the Answer" chat

A weekly feature on Paul McCartney's website is "You Gave Me the Answer," a column where he answers questions.

Oftentimes, it's generally full of Paul saying the same old stuff about the same old stuff, but this week there's some interesting conversation about the mechanics of playing guitar and songwriting:

Several of us here at play instruments and we’ve always been delighted and impressed by how intricate and complex Paul’s arrangements can be. ‘You Gave Me The Answer’ is a great example with Paul employing F diminished, G# diminished and Bb diminished; chords not often found in pop songs!
We wanted to geek out a little, so our question to Paul was this:
"You have famously talked about how you jumped on a bus across Liverpool to learn the chord B7 from a guy who knew how to play it. How did you get from there to using the more complicated diminished and augmented chords that began appearing on the early Beatles albums and have continued to be used in your songs such as ‘You Gave Me The Answer’"?
We sat down with Paul in his London office just before he left to continue his ‘Out There’ tour of the US. And boy, were we in for a treat!
Paul told us,
“It was a combination of three ways, really. Some were from people showing them to us; for example, Jim Gretty who was a guy from a guitar shop in Liverpool called Hessy’s. He had a guitar and was a jazz player, and I remember him showing us a chord that was F, but it had a couple of notes added. We called it F demented!"
Paul then picked up the acoustic guitar that lives in his office and began playing the F demented chord. You have to really stretch your fingers to make the chord, but Paul did it
with ease.
“The chord found its way into a lot of things, like ‘Michelle.’  Another chord came in via ‘Along Came Jones’ by The Coasters.”
Paul again illustrated his point by playing 'Michelle' followed by 'Along Came Jones' by The Coasters. (Check out The Coasters' song when you get chance, it's a great tune!)
"Sometimes we would pick them up from sheet music, like, 'Oh! We don’t know that chord'. But mainly it was just figuring it out from listening to songs we liked. We knew that
something went up in the chords, so me and George would work it out. Buddy Holly would use an odd chord like that - ‘Raining In My Heart’ - and the second chord in there was
augmented. We worked a lot of that out by ear. There’d also be songs like 'Til There Was You’ that would have these chords in too."
Paul then told us whilst laughing, "Sometimes we’d be working with people who knew notation and stuff and they would say, 'Is that C diminished? Is that the chord?' And we’d
look at each other, shrug and go, 'Yes!'"
Then, almost as an encore to our question, Paul played us 'Raining In My Heart' by Buddy Holly.
 P.S. F-diminished isn't really so tough.