> Consider this: music as metaphor, which surely existed before the Beatles, became required for any serious critical acceptance. Before that, Rock and Roll was pure bubblegum, and afterwards: a political force.

I think there's a tendency music fans have of overstating the impact of the bands they like (Velvet Underground is another good example). But from what I've seen, there very rarely is a case where a single musician or band comes along and single-handedly changes everything. Usually there are a lot of musicians influenced by and playing off each other that move along a general trend, and from what I've listened to that was very much what was happening in the 60's.

In terms of lyrical complexity and political commentary in modern American pop music, I'd say that a lot of that starts happening in the more folk-aligned circles (such as Simon and Garfunkel or Dylan) before you see its influence in other groups like the Beatles.

What does "music as metaphor" mean?

Rock'n'roll may have been mostly dance music, but Jazz, Folk, Blues, Chanson etc. already existed before Beatles. And songs like Yesterday or Let it Be are not really rock'n'roll anymore than say Jacques Brel is.

It means a song can be written such that none of the lyrics, if taken by their literal meanings, betray what the song is about. The entire meaning and content of the song is never stated, it requires one to identify words and phrases used in opposition to their normal usage, and realize an alternative meaning that typically connects opposing ideas in colorful ways. Such as "his intelligence was slothish, capable of amazing feats of inactivity..."