A GREAT debate! What changed music?

I'd go for All of the above plus!

The main thing that has changed music the MOST in the 20th Century (or ANY century come to that) is the Human Desire for experimentation. Examples of this being:

Beethoven writing Symphonies twice the length of the norm; shocking at the time.

The move away from writing purely Tonal music by the likes of Webern, Schoenburg and Berg.

The coming of the minimalist movement and the work of composers like Philip Glass, Steve Reich and John Adams. The most striking example has to be John Cage's work culminating in the purely silent 4' 33''..........I actually have a CD of a performance of this.

Miles Davis developing the idea of "Fusion" from which came the inspiration for a lot of bands that we have on AM.

And just to get a bit of British interest here the desire to write extended theme works by the likes of The Moody Blues, Yes and Jethro Tull were an important part of the development of Prog.

Yesspaz, your list is extensive and extemely valid but without the Human Spirit.........who knows what we'd be listening to.

Thank God for Human Spirit!

As an afterthought.

The use of narcotics, especially L.S.D. caused a massive change in music. The Beatles, Pink Floyd and Hawkwind wouldn't have written some of their greatest work if it hadn't been for the odd trip or two.