We’ve been thinking of this ever since we read the Pop Machine April 30 posting at the Chicago Tribune’s Web site, where author Mark Caro describes “Rock ‘n’ Roll,” a play written by Tom Stoppard utilizing three decades of songs to tell the tale of an unreformed Czech communist living in Cambridge, England.

“Rock ‘n’ Roll,” according to Caro, also includes other characters such as a woman “inspired and haunted by the beatific image of drug-addled visionary Syd Barrett of Pink Floyd tooling around Cambridge,” as well as the commie’s protégé who loves music and spends most of his time traveling between Prague and Cambridge.

Writes Caro:

“As usual, Stoppard has many metaphors at work: the contrast between the young, pie-eyed Barrett and his older, lost self (as well as his cynical-minded bandmates) offering an allegory on communism, while The Rolling Stones’ progression from the ‘60s to the ‘90s tells a tale of capitalism.”

Okay, we get it. Music as an allegory for the times. Nothing new there. But what songs have changed the world? Caro mentions a few good candidates, such as Bob Dylan’s “The Times They Are A-Changin’” and John Lennon’s “Imagine,” but we think you can do better.

What’s more, we’ll start this one off for you. “Do They Know It’s Christmas?” written by Bob Geldof and Midge Ure and sung by an all-star Brit collection of artists in 1984 led to “We Are The World,” and Live Aid in 1985.

Now it’s your turn. Think it over and then tell us which songs changed the world.  While you’re mulling that over, you can read the entire Pop Machine posting by clicking here.