Whatever your favourite theory of creativity, Paul McCartney has a cheery thumbs-up to offer. You think the secret is putting in the hours? ‘We played nearly 300 times in Hamburg between 1960 and 1962.’ Or could it be a wide range of cultural inputs to assimilate and remix? The Arty Beatle hoovered up Shakespeare, Dryden, not just Desmond but Thomas Dekker, Berio and Cage and rock’n’roll and light jazz, and sublimated them all.