They were not schooled in music theory nor did they ever even take music lessons, yet they instinctively knew everything they needed to create the songs they wanted. They didn't know the technical words or concepts yet they utilized them constantly. How is this possible? Pure instinct? Really, I think they actually were "geniuses"-- I hate to use that over-used word but how else to explain it?
Here's an excerpt from Jonathan Gould's book, in which he writes about the song, A Hard Day's Night:
It begins with a musical wake-up call: the harsh clang of a solitary guitar chord that hangs in the air for an elongated moment, its densely-packed notes swimming into focus like eyes adjusting to the light. (Though the song is in the key of G, this opening chord is a D minor 11th, as if a C-major triad were being played over a D-minor triad.) Two bars later, reality rushes in, as John's vocal pickup ("It's been a..." ) is swept up and carried along by a swift current of guitars, bass, drums...The momentum builds through another verse until, with a shout, the singers seem to leap out of the path of Harrison's twelve-string electric guitar and George Martin's piano as they combine on a deep, bluesy run that resolves in a delighted little jig-step of sixteen notes.The singing returns, the middle repeats, and finally, a full three minutes after it began, the song heads wearily for home, the band slowing imperceptibly, until the rhythm falls out and George's twelve-string explodes into the chord that opened the song--arpeggiated this time, its notes distinct and shimmering like stars against the sky.
Wow