 According to cultural historian Simon Philo, "Revolver" contained "[the] most sustained deployment of Indian instruments, musical form and even religious philosophy" heard in popular music up to that time.In its lyrical themes, the album marks a radical departure from the Beatles' past work, as a large majority of the songs avoid the subject of love.Author and critic Kenneth Womack writes of the Beatles exploring "phenomenologies of consciousness" on "Revolver", and he cites as examples "I'm Only Sleeping" preoccupation with dreams and the references to death in the lyrics to "Tomorrow Never Knows".